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1.
Mikko Tikkanen Michele Grieco Saijaliisa Kangasj?rvi Eva-Mari Aro 《Plant physiology》2010,152(2):723-735
Several proteins of photosystem II (PSII) and its light-harvesting antenna (LHCII) are reversibly phosphorylated according to light quantity and quality. Nevertheless, the interdependence of protein phosphorylation, nonphotochemical quenching, and efficiency of electron transfer in the thylakoid membrane has remained elusive. These questions were addressed by investigating in parallel the wild type and the stn7, stn8, and stn7 stn8 kinase mutants of Arabidopsis (Arabidopsis thaliana), using the stn7 npq4, npq4, npq1, and pgr5 mutants as controls. Phosphorylation of PSII-LHCII proteins is strongly and dynamically regulated according to white light intensity. Yet, the changes in phosphorylation do not notably modify the relative excitation energy distribution between PSII and PSI, as typically occurs when phosphorylation is induced by “state 2” light that selectively excites PSII and induces the phosphorylation of both the PSII core and LHCII proteins. On the contrary, under low-light conditions, when excitation energy transfer from LHCII to reaction centers is efficient, the STN7-dependent LHCII protein phosphorylation guarantees a balanced distribution of excitation energy to both photosystems. The importance of this regulation diminishes at high light upon induction of thermal dissipation of excitation energy. Lack of the STN7 kinase, and thus the capacity for equal distribution of excitation energy to PSII and PSI, causes relative overexcitation of PSII under low light but not under high light, leading to disturbed maintenance of fluent electron flow under fluctuating light intensities. The physiological relevance of the STN7-dependent regulation is evidenced by severely stunted phenotypes of the stn7 and stn7 stn8 mutants under strongly fluctuating light conditions.Several proteins of PSII and its light-harvesting antenna (LHCII) are reversibly phosphorylated by the STN7 and STN8 kinase-dependent pathways according to the intensity and quality of light (Bellafiore et al., 2005; Bonardi et al., 2005). The best-known phosphorylation-dependent phenomenon in the thylakoid membrane is the state transition: a regulatory mechanism that modulates the light-harvesting capacity between PSII and PSI. According to the traditional view, “state 1” prevails when plants are exposed to far-red light (state 1 light), which selectively excites PSI. Alternatively, thylakoids are in “state 2” when plants are exposed to blue or red light (state 2 light), favoring PSII excitation. In state 1, the yield of fluorescence from PSII is higher in comparison with state 2 (for review, see Allen and Forsberg, 2001). State transitions are dependent on the phosphorylation of LHCII proteins (Bellafiore et al., 2005) and their association with PSI proteins, particularly PSI-H (Lunde et al., 2000). Under state 2 light, both the PSII core and LHCII proteins are strongly phosphorylated, whereas the state 1 light induces dephosphorylation of both the PSII core and LHCII phosphoproteins (Piippo et al., 2006; Tikkanen et al., 2006). In nature, however, such extreme changes in light quality rarely occur. The intensity of light, on the contrary, fluctuates frequently in all natural habitats occupied by photosynthetic organisms, thus constantly modulating the extent of thylakoid protein phosphorylation in a highly dynamic manner (Tikkanen et al., 2008a).The regulation of PSII-LHCII protein phosphorylation by the quantity of light is much more complex than the regulatory circuits induced by the state 1 and state 2 lights. Whereas changes in light quality induce a concurrent increase or decrease in the phosphorylation levels of both the PSII core (D1, D2, and CP43) and LHCII (Lhcb1 and Lhcb2) proteins, the changes in white light intensity may influence the kinetics of PSII core and LHCII protein phosphorylation in higher plant chloroplasts even in opposite directions (Tikkanen et al., 2008a). Indeed, it is well documented that low light (LL; i.e. lower than that generally experienced during growth) induces strong phosphorylation of LHCII but relatively weak phosphorylation of the PSII core proteins. Exposure of plants to high light (HL) intensities, on the contrary, promotes the phosphorylation of PSII core proteins but inhibits the activity of the LHCII kinase, leading to dephosphorylation of LHCII proteins (Rintamäki et al., 2000; Hou et al., 2003).Thylakoid protein phosphorylation induces dynamic migrations of PSII-LHCII proteins along the thylakoid membrane (Bassi et al., 1988; Iwai et al., 2008) and modulation of thylakoid ultrastructure (Chuartzman et al., 2008). According to the traditional state transition theory, the phosphorylation of LHCII proteins decreases the antenna size of PSII and increases that of PSI, which is reflected as a quenched fluorescence emission from PSII. Alternatively, subsequent dephosphorylation of LHCII increases the antenna size of PSII and decreases that of PSI, which in turn is seen as increased PSII fluorescence (Bennett et al., 1980; Allen et al., 1981; Allen and Forsberg, 2001). This view was recently challenged based on studies with thylakoid membrane fractions, revealing that modulations in the relative distribution of excitation energy between PSII and PSI by LHCII phosphorylation specifically occur in the areas of grana margins, where both PSII and PSI function under the same antenna system, and the energy distribution between the photosystems is regulated via a more subtle mechanism than just the robust migration of phosphorylated LHCII (Tikkanen et al., 2008b). It has also been reported that most of the PSI reaction centers are located in the grana margins in a close vicinity to PSII-LHCII-rich grana thylakoids (Kaftan et al., 2002), providing a perfect framework for the regulation of excitation energy distribution from LHCII to both PSII and PSI.When considering the natural light conditions, the HL intensities are the only known light conditions that in higher plant chloroplasts specifically dephosphorylate only the LHCII proteins but not the PSII core proteins. However, such light conditions do not lead to enhanced function of PSII. Instead, the HL conditions strongly down-regulate the function of PSII via nonphotochemical quenching of excitation energy (NPQ) and PSII photoinhibition (for review, see Niyogi, 1999). On the other hand, after dark acclimation of leaves and relaxation of NPQ, PSII functions much more efficiently when plants/leaves are transferred to LL despite strong phosphorylation of LHCII, as compared with the low phosphorylation state of LHCII upon transfer to HL conditions.The delicate regulation of thylakoid protein phosphorylation in higher plant chloroplasts according to prevailing light intensity is difficult to integrate with the traditional theory of state transitions (i.e. the regulation of the absorption cross-section of PSII and PSI by reversible phosphorylation of LHCII). Moreover, besides LHCII proteins, reversible phosphorylation of the PSII core proteins may also play a role in dynamic light acclimation of plants. Recently, we demonstrated that the PSII core protein phosphorylation is a prerequisite for controlled turnover of the PSII reaction center protein D1 upon photodamage (Tikkanen et al., 2008a). This, however, does not exclude the possibility that the strict regulation of PSII core protein phosphorylation is also connected to the regulation of light harvesting and photosynthetic electron transfer. Moreover, the interactions between PSII and LHCII protein phosphorylation, nonphotochemical quenching, and cyclic electron flow around PSI in the regulation of photosynthetic electron transfer reactions remain poorly understood. To gain a deeper insight into such regulatory networks, we explored the effect of strongly fluctuating white light on chlorophyll (chl) fluorescence in Arabidopsis (Arabidopsis thaliana) mutants differentially deficient in PSII-LHCII protein phosphorylation and/or the regulatory systems of NPQ. 相似文献
2.
The STN8 kinase‐PBCP phosphatase system is responsible for high‐light‐induced reversible phosphorylation of the PSII inner antenna subunit CP29 in rice
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Nico Betterle Roshan Sharma Poudyal Anthony Rosa Guangxi Wu Roberto Bassi Choon‐Hwan Lee 《The Plant journal : for cell and molecular biology》2017,89(4):681-691
Reversible phosphorylation of thylakoid light‐harvesting proteins is a mechanism to compensate for unbalanced excitation of photosystem I (PSI) versus photosystem II (PSII) under limiting light. In monocots, an additional phosphorylation event on the PSII antenna CP29 occurs upon exposure to excess light, enhancing resistance to light stress. Different from the case of the major LHCII antenna complex, the STN7 kinase and its related PPH1 phosphatase were proven not to be involved in CP29 phosphorylation, indicating that a different set of enzymes act in the high‐light (HL) response. Here, we analyze a rice stn8 mutant in which both PSII core proteins and CP29 phosphorylation are suppressed in HL, implying that STN8 is the kinase catalyzing this reaction. In order to identify the phosphatase involved, we produced a recombinant enzyme encoded by the rice ortholog of AtPBCP, antagonist of AtSTN8, which catalyzes the dephosphorylation of PSII core proteins. The recombinant protein was active in dephosphorylating P‐CP29. Based on these data, we propose that the activities of the OsSTN8 kinase and the antagonistic OsPBCP phosphatase, in addition to being involved in the repair of photo‐damaged PSII, are also responsible for the HL‐dependent reversible phosphorylation of the inner antenna CP29. 相似文献
3.
Caterina Gerotto Andrea Trotta Azfar Ali Bajwa Tomas Morosinotto Eva-Mari Aro 《Plant physiology》2022,190(1):698
Reversible thylakoid protein phosphorylation provides most flowering plants with dynamic acclimation to short-term changes in environmental light conditions. Here, through generating Serine/Threonine protein kinase 7 (STN7)-depleted mutants in the moss Physcomitrella (Physcomitrium patens), we identified phosphorylation targets of STN7 kinase and their roles in short- and long-term acclimation of the moss to changing light conditions. Biochemical and mass spectrometry analyses revealed STN7-dependent phosphorylation of N-terminal Thr in specific Light-Harvesting Complex II (LHCII) trimer subunits (LHCBM2 and LHCBM4/8) and provided evidence that phospho-LHCBM accumulation is responsible for the assembly of two distinct Photosystem I (PSI) supercomplexes (SCs), both of which are largely absent in STN7-depleted mutants. Besides the canonical state transition complex (PSI-LHCI-LHCII), we isolated the larger moss-specific PSI-Large (PSI-LHCI-LHCB9-LHCII) from stroma-exposed thylakoids. Unlike PSI-LHCI-LHCII, PSI-Large did not demonstrate short-term dynamics for balancing the distribution of excitation energy between PSII and PSI. Instead, PSI-Large contributed to a more stable increase in PSI antenna size in Physcomitrella, except under prolonged high irradiance. Additionally, the STN7-depleted mutants revealed altered light-dependent phosphorylation of a monomeric antenna protein, LHCB6, whose phosphorylation displayed a complex regulation by multiple kinases. Collectively, the unique phosphorylation plasticity and dynamics of Physcomitrella monomeric LHCB6 and trimeric LHCBM isoforms, together with the presence of PSI SCs with different antenna sizes and responsiveness to light changes, reflect the evolutionary position of mosses between green algae and vascular plants, yet with clear moss-specific features emphasizing their adaptation to terrestrial low-light environments.Phosphorylation-dependent formation of photosystem I supercomplexes provides both short- and long-term acclimation of moss photosynthetic apparatus to changing environmental cues. 相似文献
4.
Samol I Shapiguzov A Ingelsson B Fucile G Crèvecoeur M Vener AV Rochaix JD Goldschmidt-Clermont M 《The Plant cell》2012,24(6):2596-2609
Reversible protein phosphorylation plays a major role in the acclimation of the photosynthetic apparatus to changes in light. Two paralogous kinases phosphorylate subsets of thylakoid membrane proteins. STATE TRANSITION7 (STN7) phosphorylates LHCII, the light-harvesting antenna of photosystem II (PSII), to balance the activity of the two photosystems through state transitions. STN8, which is mainly involved in phosphorylation of PSII core subunits, influences folding of the thylakoid membranes and repair of PSII after photodamage. The rapid reversibility of these acclimatory responses requires the action of protein phosphatases. In a reverse genetic screen, we identified the chloroplast PP2C phosphatase, PHOTOSYSTEM II CORE PHOSPHATASE (PBCP), which is required for efficient dephosphorylation of PSII proteins. Its targets, identified by immunoblotting and mass spectrometry, largely coincide with those of the kinase STN8. The recombinant phosphatase is active in vitro on a synthetic substrate or on isolated thylakoids. Thylakoid folding is affected in the absence of PBCP, while its overexpression alters the kinetics of state transitions. PBCP and STN8 form an antagonistic kinase and phosphatase pair whose substrate specificity and physiological functions are distinct from those of STN7 and the counteracting phosphatase PROTEIN PHOSPHATASE1/THYLAKOID-ASSOCIATED PHOSPHATASE38, but their activities may overlap to some degree. 相似文献
5.
Nageswara Rao Mekala Marjaana Suorsa Marjaana Rantala Eva-Mari Aro Mikko Tikkanen 《Plant physiology》2015,168(2):721-734
Photosystem II (PSII) core and light-harvesting complex II (LHCII) proteins in plant chloroplasts undergo reversible phosphorylation upon changes in light intensity (being under control of redox-regulated STN7 and STN8 kinases and TAP38/PPH1 and PSII core phosphatases). Shift of plants from growth light to high light results in an increase of PSII core phosphorylation, whereas LHCII phosphorylation concomitantly decreases. Exactly the opposite takes place when plants are shifted to lower light intensity. Despite distinct changes occurring in thylakoid protein phosphorylation upon light intensity changes, the excitation balance between PSII and photosystem I remains unchanged. This differs drastically from the canonical-state transition model induced by artificial states 1 and 2 lights that concomitantly either dephosphorylate or phosphorylate, respectively, both the PSII core and LHCII phosphoproteins. Analysis of the kinase and phosphatase mutants revealed that TAP38/PPH1 phosphatase is crucial in preventing state transition upon increase in light intensity. Indeed, tap38/pph1 mutant revealed strong concomitant phosphorylation of both the PSII core and LHCII proteins upon transfer to high light, thus resembling the wild type under state 2 light. Coordinated function of thylakoid protein kinases and phosphatases is shown to secure balanced excitation energy for both photosystems by preventing state transitions upon changes in light intensity. Moreover, PROTON GRADIENT REGULATION5 (PGR5) is required for proper regulation of thylakoid protein kinases and phosphatases, and the pgr5 mutant mimics phenotypes of tap38/pph1. This shows that there is a close cooperation between the redox- and proton gradient-dependent regulatory mechanisms for proper function of the photosynthetic machinery.Photosynthetic light reactions take place in the chloroplast thylakoid membrane. Primary energy conversion reactions are performed by synchronized function of the two light energy-driven enzymes PSII and PSI. PSII uses excitation energy to split water into electrons and protons. PSII feeds electrons to the intersystem electron transfer chain (ETC) consisting of plastoquinone, cytochrome b6f, and plastocyanin. PSI oxidizes the ETC in a light-driven reduction of NADP to NADPH. Light energy is collected by the light-harvesting antenna systems in the thylakoid membrane composed of specific pigment-protein complexes (light-harvesting complex I [LHCI] and LHCII). The majority of the light-absorbing pigments are bound to LHCII trimers that can serve the light harvesting of both photosystems (Galka et al., 2012; Kouřil et al., 2013; Wientjes et al., 2013b). Energy distribution from LHCII is regulated by protein phosphorylation (Bennett, 1979; Bennett et al., 1980; Allen et al., 1981) under control of the STN7 and STN8 kinases (Depège et al., 2003; Bellafiore et al., 2005; Bonardi et al., 2005; Vainonen et al., 2005) and the TAP38/PPH1 and Photosystem II Core Phosphatase (PBCP) phosphatases (Pribil et al., 2010; Shapiguzov et al., 2010; Samol et al., 2012). LHCII trimers are composed of LHCB1, LHCB2, and LHCB3 proteins, and in addition to reversible phosphorylation of LHCB1 and LHCB2, the protein composition of the LHCII trimers also affects the energy distribution from the light-harvesting system to photosystems (Damkjaer et al., 2009; Pietrzykowska et al., 2014). Most of the LHCII trimers are located in the PSII-rich grana membranes and PSII- and PSI-rich grana margins of the thylakoid membrane, and only a minor fraction resides in PSI- and ATP synthase-rich stroma lamellae (Tikkanen et al., 2008b; Suorsa et al., 2014). Both photosystems bind a small amount of LHCII trimers in biochemically isolatable PSII-LHCII and PSI-LHCII complexes (Pesaresi et al., 2009; Järvi et al., 2011; Caffarri et al., 2014). The large portion of the LHCII, however, does not form isolatable complexes with PSII or PSI, and therefore, it separates as free LHCII trimers upon biochemical fractionation of the thylakoid membrane by Suc gradient centrifugation or in native gel analyses (Caffarri et al., 2009; Järvi et al., 2011), the amount being dependent on the thylakoid isolation method. Nonetheless, in vivo, this major LHCII antenna fraction serves the light-harvesting function. This is based on the fact that fluorescence from free LHCII, peaking at 680 nm in 77-K fluorescence emission spectra, can only be detected when the energy transfer properties of the thylakoid membrane are disturbed by detergents (Grieco et al., 2015).Regulation of excitation energy distribution from LHCII to PSII and PSI has, for decades, been linked to LHCII phosphorylation and state transitions (Bennett, 1979; Bennett et al., 1980; Allen et al., 1981). It has been explained that a fraction of LHCII gets phosphorylated and migrates from PSII to PSI, which can be evidenced as increase in PSI cross section and was assigned as transition to state 2 (for review, see Allen, 2003; Rochaix et al., 2012). The LHCII proteins are, however, phosphorylated all over the thylakoid membrane (i.e. in the PSII- and LHCII-rich grana core) in grana margins containing PSII, LHCII, and PSI as well as in PSI-rich stroma lamellae also harboring PSII-LHCII, LHCII, and PSI-LHCII complexes in minor amounts (Tikkanen et al., 2008b; Grieco et al., 2012; Leoni et al., 2013; Wientjes et al., 2013a)—making the canonical-state transition theory inadequate to explain the physiological role of reversible LHCII phosphorylation (Tikkanen and Aro, 2014). Moreover, the traditional-state transition model is based on lateral segregation of PSII-LHCII and PSI-LHCI to different thylakoid domains. It, however, seems likely that PSII and PSI are energetically connected through a shared light-harvesting system composed of LHCII trimers (Grieco et al., 2015), and there is efficient excitation energy transfer between the two photosystems (Yokono et al., 2015). Nevertheless, it is clear that LHCII phosphorylation is a prerequisite to form an isolatable PSI-LHCII complex called the state transition complex (Pesaresi et al., 2009; Järvi et al., 2011). Existence of a minor state transition complex, however, does not explain why LHCII is phosphorylated all over the thylakoid membrane and how the energy transfer is regulated from the majority of LHCII antenna that is shared between PSII and PSI but does not form isolatable complexes with them (Grieco et al., 2015).Plants grown under any steady-state white light condition show the following characteristics of the thylakoid membrane: PSII core and LHCII phosphoproteins are moderately phosphorylated, phosphorylation takes place all over the thylakoid membrane, and the PSI-LHCII state transition complex is present (Järvi et al., 2011; Grieco et al., 2012; Wientjes et al., 2013b). Upon changes in the light intensity, the relative phosphorylation level between PSII core and LHCII phosphoproteins drastically changes (Rintamäki et al., 1997, 2000) in the timescale of 5 to 30 min. When light intensity increases, the PSII core protein phosphorylation increases, whereas the level of LHCII phosphorylation decreases. On the contrary, a decrease in light intensity decreases the phosphorylation level of PSII core proteins but strongly increases the phosphorylation of the LHCII proteins (Rintamäki et al., 1997, 2000). The presence and absence of the PSI-LHCII state transition complex correlate with LHCII phosphorylation (similar to the state transitions; Pesaresi et al., 2009; Wientjes et al., 2013b). Despite all of these changes in thylakoid protein phosphorylation, the relative excitation of PSII and PSI (i.e. the absorption cross section of PSII and PSI measured by 77-K fluorescence) remains nearly unchanged upon changes in white-light intensity (i.e. no state transitions can be observed despite massive differences in LHCII protein phosphorylation; Tikkanen et al., 2010).The existence of the opposing behaviors of PSII core and LHCII protein phosphorylation, as described above, has been known for more than 15 years (Rintamäki et al., 1997, 2000), but the physiological significance of this phenomenon has remained elusive. It is known that PSII core protein phosphorylation in high light (HL) facilitates the unpacking of PSII-LHCII complexes required for proper processing of the damaged PSII centers and thus, prevents oxidative damage of the photosynthetic machinery (Tikkanen et al., 2008a; Fristedt et al., 2009; Goral et al., 2010; Kirchhoff et al., 2011). It is also known that the damaged PSII core protein D1 needs to be dephosphorylated before its proteolytic degradation upon PSII turnover (Koivuniemi et al., 1995). There is, however, no coherent understanding available to explain why LHCII proteins are dephosphorylated upon exposure of plants to HL and PSII core proteins are dephosphorylated upon exposure to low light (LL).The above-described light quantity-dependent control of thylakoid protein phosphorylation drastically differs from the light quality-dependent protein phosphorylation (Tikkanen et al., 2010). State transitions are generally investigated by using different light qualities, preferentially exciting either PSI or PSII. State 1 light favors PSI excitation, leading to oxidation of the ETC and dephosphorylation of both the PSII core and LHCII proteins. State 2 light, in turn, preferentially excites PSII, leading to reduction of ETC and strong concomitant phosphorylation of both the PSII core and LHCII proteins (Haldrup et al., 2001). Shifts between states 1 and 2 lights induce state transitions, mechanisms that change the excitation between PSII and PSI (Murata and Sugahara, 1969; Murata, 2009). Similar to shifts between state lights, the shifts between LL and HL intensity also change the phosphorylation of the PSII core and LHCII proteins (Rintamäki et al., 1997, 2000). Importantly, the white-light intensity-induced changes in thylakoid protein phosphorylation do not change the excitation energy distribution between the two photosystems (Tikkanen et al., 2010). Despite this fundamental difference between the light quantity- and light quality-induced thylakoid protein phosphorylations, a common feature for both mechanisms is a strict requirement of LHCII phosphorylation for formation of the PSI-LHCII complex. However, it is worth noting that LHCII phosphorylation under state 2 light is not enough to induce the state 2 transition but that the P-LHCII docking proteins in the PSI complex are required (Lunde et al., 2000; Jensen et al., 2004; Zhang and Scheller, 2004; Leoni et al., 2013).Thylakoid protein phosphorylation is a dynamic redox-regulated process dependent on the interplay between two kinases (STN7 and STN8; Depège et al., 2003; Bellafiore et al., 2005; Bonardi et al., 2005; Vainonen et al., 2005) and two phosphatases (TAP38/PPH1 and PBCP; Pribil et al., 2010; Shapiguzov et al., 2010; Samol et al., 2012). Concerning the redox regulation mechanisms in vivo, only the LHCII kinase (STN7) has so far been thoroughly studied (Vener et al., 1997; Rintamäki et al., 2000; Lemeille et al., 2009). The STN7 kinase is considered as the LHCII kinase, and indeed, it phosphorylates the LHCB1 and LHCB2 proteins (Bellafiore et al., 2005; Bonardi et al., 2005; Tikkanen et al., 2006). In addition to this, STN7 takes part in the phosphorylation of PSII core proteins (Vainonen et al., 2005), especially in LL (Tikkanen et al., 2008b, 2010). The STN8 kinase is required for phosphorylation of PSII core proteins in HL but does not significantly participate in phosphorylation of LHCII (Bellafiore et al., 2005; Bonardi et al., 2005; Vainonen et al., 2005; Tikkanen et al., 2010). It has been shown that, in traditional state 1 condition, which oxidizes the ETC, the dephosphorylation of LHCII is dependent on TAP38/PPH1 phosphatase (Pribil et al., 2010; Shapiguzov et al., 2010), whereas the PSII core protein dephosphorylation is dependent on the PBCP phosphatase (Samol et al., 2012). However, it remains unresolved whether and how the TAP38/PPH1 and PBCP phosphatases are involved in the light intensity-dependent regulation of thylakoid protein phosphorylation typical for natural environments.Here, we have used the two kinase (stn7 and stn8) and the two phosphatase (tap38/pph1and pbcp) mutants of Arabidopsis (Arabidopsis thaliana) to elucidate the individual roles of these enzymes in reversible thylakoid protein phosphorylation and distribution of excitation energy between PSII and PSI upon changes in light intensity. It is shown that the TAP38/PPH1-dependent, redox-regulated LHCII dephosphorylation is the key component to maintain excitation balance between PSII and PSI upon increase in light intensity, which at the same time, induces strong phosphorylation of the PSII core proteins. Collectively, reversible but opposite phosphorylation and dephosphorylation of the PSII core and LHCII proteins upon increase or decrease in light intensity are shown to be crucial for maintenance of even distribution of excitation energy to both photosystems, thus preventing state transitions. Moreover, evidence is provided indicating that the pH gradient across the thylakoid membrane is yet another important component in regulation of the distribution of excitation energy to PSII and PSI, possibly by affecting the regulation of thylakoid kinases and phosphatases. 相似文献
6.
Jean-David Rochaix Sylvain Lemeille Alexey Shapiguzov Iga Samol Geoffrey Fucile Adrian Willig Michel Goldschmidt-Clermont 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2012,367(1608):3466-3474
Photosynthetic organisms are subjected to frequent changes in light quality and quantity and need to respond accordingly. These acclimatory processes are mediated to a large extent through thylakoid protein phosphorylation. Recently, two major thylakoid protein kinases have been identified and characterized. The Stt7/STN7 kinase is mainly involved in the phosphorylation of the LHCII antenna proteins and is required for state transitions. It is firmly associated with the cytochrome b6f complex, and its activity is regulated by the redox state of the plastoquinone pool. The other kinase, Stl1/STN8, is responsible for the phosphorylation of the PSII core proteins. Using a reverse genetics approach, we have recently identified the chloroplast PPH1/TAP38 and PBPC protein phosphatases, which counteract the activity of STN7 and STN8 kinases, respectively. They belong to the PP2C-type phosphatase family and are conserved in land plants and algae. The picture that emerges from these studies is that of a complex regulatory network of chloroplast protein kinases and phosphatases that is involved in light acclimation, in maintenance of the plastoquinone redox poise under fluctuating light and in the adjustment to metabolic needs. 相似文献
7.
State transitions revisited—a buffering system for dynamic low light acclimation of Arabidopsis 总被引:2,自引:0,他引:2
Tikkanen M Mikko T Piippo M Mirva P Suorsa M Marjaana S Sirpiö S Sari S Mulo P Paula M Vainonen J Julia V Vener AV Alexander V Allahverdiyeva Y Yagut A Aro EM Eva-Mari A 《Plant molecular biology》2006,62(4-5):779-793
8.
Redox signalling and the structural basis of regulation of photosynthesis by protein phosphorylation 总被引:1,自引:0,他引:1
In photosynthesis in chloroplasts and cyanobacteria, redox control of thylakoid protein phosphorylation regulates distribution of absorbed excitation energy between the two photosystems. When electron transfer through chloroplast photosystem II (PSII) proceeds at a rate higher than that through photosystem I (PSI), chemical reduction of a redox sensor activates a thylakoid protein kinase that catalyses phosphorylation of light-harvesting complex II (LHCII). Phosphorylation of LHCII increases its affinity for PSI and thus redistributes light-harvesting chlorophyll to PSI at the expense of PSII. This short-term redox signalling pathway acts by means of reversible, post-translational modification of pre-existing proteins. A long-term equalisation of the rates of light utilisation by PSI and PSII also occurs: by means of adjustment of the stoichiometry of PSI and PSII. It is likely that the same redox sensor controls both state transitions and photosystem stoichiometry. A specific mechanism for integration of these short- and long-term adaptations is proposed. Recent evidence shows that phosphorylation of LHCII causes a change in its 3-D structure, which implies that the mechanism of state transitions in chloroplasts involves control of recognition of PSI and PSII by LHCII. The distribution of LHCII between PSII and PSI is therefore determined by the higher relative affinity of phospho-LHCII for PSI, with lateral movement of the two forms of the LHCII being simply a result of their diffusion within the membrane plane. Phosphorylation-induced dissociation of LHCII trimers may induce lateral movement of monomeric phospho-LHCII, which binds preferentially to PSI. After dephosphorylation, monomeric, unphosphorylated LHCII may trimerize at the periphery of PSII. 相似文献
9.
Pádraic J. Flood Lan Yin Andrei Herdean Jeremy Harbinson Mark G. M. Aarts Cornelia Spetea 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2014,369(1640)
Reversible phosphorylation of photosystem II (PSII) proteins is an important regulatory mechanism that can protect plants from changes in ambient light intensity and quality. We hypothesized that there is natural variation in this process in Arabidopsis (Arabidopsis thaliana), and that this results from genetic variation in the STN7 and STN8 kinase genes. To test this, Arabidopsis accessions of diverse geographical origins were exposed to two light regimes, and the levels of phospho-D1 and phospho-light harvesting complex II (LHCII) proteins were quantified by western blotting with anti-phosphothreonine antibodies. Accessions were classified as having high, moderate or low phosphorylation relative to Col-0. This variation could not be explained by the abundance of the substrates in thylakoid membranes. In genotypes with atrazine-resistant forms of the D1 protein, low D1 and LHCII protein phosphorylation was observed, which may be due to low PSII efficiency, resulting in reduced activation of the STN kinases. In the remaining genotypes, phospho-D1 levels correlated with STN8 protein abundance in high-light conditions. In growth light, D1 and LHCII phosphorylation correlated with longitude and in the case of LHCII phosphorylation also with temperature variability. This suggests a possible role of natural variation in PSII protein phosphorylation in the adaptation of Arabidopsis to diverse environments. 相似文献
10.
Phosphorylation-dependent regulation of excitation energy distribution between the two photosystems in higher plants 总被引:2,自引:0,他引:2
Tikkanen M Nurmi M Suorsa M Danielsson R Mamedov F Styring S Aro EM 《Biochimica et biophysica acta》2008,1777(5):425-432
Phosphorylation-dependent movement of the light-harvesting complex II (LHCII) between photosystem II (PSII) and photosystem I (PSI) takes place in order to balance the function of the two photosystems. Traditionally, the phosphorylatable fraction of LHCII has been considered as the functional unit of this dynamic regulation. Here, a mechanical fractionation of the thylakoid membrane of Spinacia oleracea was performed from leaves both in the phosphorylated state (low light, LL) and in the dephosphorylated state (dark, D) in order to compare the phosphorylation-dependent protein movements with the excitation changes occurring in the two photosystems upon LHCII phosphorylation. Despite the fact that several LHCII proteins migrate to stroma lamellae when LHCII is phosphorylated, no increase occurs in the 77 K fluorescence emitted from PSI in this membrane fraction. On the contrary, such an increase in fluorescence occurs in the grana margin fraction, and the functionally important mobile unit is the PSI-LHCI complex. A new model for LHCII phosphorylation driven regulation of relative PSII/PSI excitation thus emphasises an increase in PSI absorption cross-section occurring in grana margins upon LHCII phosphorylation and resulting from the movement of PSI-LHCI complexes from stroma lamellae and subsequent co-operation with the P-LHCII antenna from the grana. The grana margins probably give a flexibility for regulation of linear and cyclic electron flow in plant chloroplasts. 相似文献
11.
Hansson M Dupuis T Strömquist R Andersson B Vener AV Carlberg I 《The Journal of biological chemistry》2007,282(22):16214-16222
The localization of the plant-specific thylakoid-soluble phosphoprotein of 9 kDa, TSP9, within the chloroplast thylakoid membrane of spinach has been established by the combined use of fractionation, immunoblotting, cross-linking, and mass spectrometry. TSP9 was found to be exclusively confined to the thylakoid membranes, where it is enriched in the stacked grana membrane domains. After mild solubilization of the membranes, TSP9 migrated together with the major light-harvesting antenna (LHCII) of photosystem II (PSII) and with PSII-LHCII supercomplexes upon separation of the protein complexes by either native gel electrophoresis or sucrose gradient centrifugation. Studies with a cleavable cross-linking agent revealed the interaction of TSP9 with both major and minor LHCII proteins as identified by mass spectrometric sequencing. Cross-linked complexes that in addition to TSP9 contain the peripheral PSII subunits CP29, CP26, and PsbS, which form the interface between LHCII and the PSII core, were found. Our observations also clearly suggest an interaction of TSP9 with photosystem I (PSI) as shown by both immunodetection and mass spectrometry. Sequencing identified the peripheral PSI subunits PsaL, PsaF, and PsaE, originating from cross-linked protein complexes of around 30 kDa that also contained TSP9. The distribution of TSP9 among the cross-linked forms was found to be sensitive to conditions such as light exposure. An association of TSP9 with LHCII as well as the peripheries of the photosystems suggests its involvement in regulation of photosynthetic light harvesting. 相似文献
12.
Phosphorylation-dependent movement of the light-harvesting complex II (LHCII) between photosystem II (PSII) and photosystem I (PSI) takes place in order to balance the function of the two photosystems. Traditionally, the phosphorylatable fraction of LHCII has been considered as the functional unit of this dynamic regulation. Here, a mechanical fractionation of the thylakoid membrane of Spinacia oleracea was performed from leaves both in the phosphorylated state (low light, LL) and in the dephosphorylated state (dark, D) in order to compare the phosphorylation-dependent protein movements with the excitation changes occurring in the two photosystems upon LHCII phosphorylation. Despite the fact that several LHCII proteins migrate to stroma lamellae when LHCII is phosphorylated, no increase occurs in the 77 K fluorescence emitted from PSI in this membrane fraction. On the contrary, such an increase in fluorescence occurs in the grana margin fraction, and the functionally important mobile unit is the PSI-LHCI complex. A new model for LHCII phosphorylation driven regulation of relative PSII/PSI excitation thus emphasises an increase in PSI absorption cross-section occurring in grana margins upon LHCII phosphorylation and resulting from the movement of PSI-LHCI complexes from stroma lamellae and subsequent co-operation with the P-LHCII antenna from the grana. The grana margins probably give a flexibility for regulation of linear and cyclic electron flow in plant chloroplasts. 相似文献
13.
Proteomic characterization of hierarchical megacomplex formation in Arabidopsis thylakoid membrane
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Marjaana Rantala Mikko Tikkanen Eva‐Mari Aro 《The Plant journal : for cell and molecular biology》2017,92(5):951-962
Conversion of solar energy into chemical energy in plant chloroplasts concomitantly modifies the thylakoid architecture and hierarchical interactions between pigment–protein complexes. Here, the thylakoids were isolated from light‐acclimated Arabidopsis leaves and investigated with respect to the composition of the thylakoid protein complexes and their association into higher molecular mass complexes, the largest one comprising both photosystems (PSII and PSI) and light‐harvesting chlorophyll a/b‐binding complexes (LHCII). Because the majority of plant light‐harvesting capacity is accommodated in LHCII complexes, their structural interaction with photosystem core complexes is extremely important for efficient light harvesting. Specific differences in the strength of LHCII binding to PSII core complexes and the formation of PSII supercomplexes are well characterized. Yet, the role of loosely bound L‐LHCII that disconnects to a large extent during the isolation of thylakoid protein complexes remains elusive. Because L‐LHCII apparently has a flexible role in light harvesting and energy dissipation, depending on environmental conditions, its close interaction with photosystems is a prerequisite for successful light harvesting in vivo. Here, to reveal the labile and fragile light‐dependent protein interactions in the thylakoid network, isolated membranes were subjected to sequential solubilization using detergents with differential solubilization capacity and applying strict quality control. Optimized 3D‐lpBN‐lpBN‐sodium dodecyl sulfate–polyacrylamide gel electrophoresis system demonstrated that PSII–LHCII supercomplexes, together with PSI complexes, hierarchically form larger megacomplexes via interactions with L‐LHCII trimers. The polypeptide composition of LHCII trimers and the phosphorylation of Lhcb1 and Lhcb2 were examined to determine the light‐dependent supramolecular organization of the photosystems into megacomplexes. 相似文献
14.
Mahendra K. Shukla Akimasa Watanabe Sam Wilson Vasco Giovagnetti Ece Imam Moustafa Jun Minagawa Alexander V. Ruban 《The Journal of biological chemistry》2020,295(51):17816
Nonphotochemical quenching (NPQ) is a mechanism of regulating light harvesting that protects the photosynthetic apparatus from photodamage by dissipating excess absorbed excitation energy as heat. In higher plants, the major light-harvesting antenna complex (LHCII) of photosystem (PS) II is directly involved in NPQ. The aggregation of LHCII is proposed to be involved in quenching. However, the lack of success in isolating native LHCII aggregates has limited the direct interrogation of this process. The isolation of LHCII in its native state from thylakoid membranes has been problematic because of the use of detergent, which tends to dissociate loosely bound proteins, and the abundance of pigment–protein complexes (e.g. PSI and PSII) embedded in the photosynthetic membrane, which hinders the preparation of aggregated LHCII. Here, we used a novel purification method employing detergent and amphipols to entrap LHCII in its natural states. To enrich the photosynthetic membrane with the major LHCII, we used Arabidopsis thaliana plants lacking the PSII minor antenna complexes (NoM), treated with lincomycin to inhibit the synthesis of PSI and PSII core proteins. Using sucrose density gradients, we succeeded in isolating the trimeric and aggregated forms of LHCII antenna. Violaxanthin- and zeaxanthin-enriched complexes were investigated in dark-adapted, NPQ, and dark recovery states. Zeaxanthin-enriched antenna complexes showed the greatest amount of aggregated LHCII. Notably, the amount of aggregated LHCII decreased upon relaxation of NPQ. Employing this novel preparative method, we obtained a direct evidence for the role of in vivo LHCII aggregation in NPQ. 相似文献
15.
Sylvain Lemeille Maria V. Turkina Alexander V. Vener Jean-David Rochaix 《Molecular & cellular proteomics : MCP》2010,9(6):1281-1295
Photosynthetic organisms are able to adapt to changes in light conditions by balancing the light excitation energy between the light-harvesting systems of photosystem (PS) II and photosystem I to optimize the photosynthetic yield. A key component in this process, called state transitions, is the chloroplast protein kinase Stt7/STN7, which senses the redox state of the plastoquinone pool. Upon preferential excitation of photosystem II, this kinase is activated through the cytochrome b6f complex and required for the phosphorylation of the light-harvesting system of photosystem II, a portion of which migrates to photosystem I (state 2). Preferential excitation of photosystem I leads to the inactivation of the kinase and to dephosphorylation of light-harvesting complex (LHC) II and its return to photosystem II (state 1). Here we compared the thylakoid phosphoproteome of the wild-type strain and the stt7 mutant of Chlamydomonas under state 1 and state 2 conditions. This analysis revealed that under state 2 conditions several Stt7-dependent phosphorylations of specific Thr residues occur in Lhcbm1/Lhcbm10, Lhcbm4/Lhcbm6/Lhcbm8/Lhcbm9, Lhcbm3, Lhcbm5, and CP29 located at the interface between PSII and its light-harvesting system. Among the two phosphorylation sites detected specifically in CP29 under state 2, one is Stt7-dependent. This phosphorylation may play a crucial role in the dissociation of CP29 from PSII and/or in its association to PSI where it serves as a docking site for LHCII in state 2. Moreover, Stt7 was required for the phosphorylation of the thylakoid protein kinase Stl1 under state 2 conditions, suggesting the existence of a thylakoid protein kinase cascade. Stt7 itself is phosphorylated at Ser533 in state 2, but analysis of mutants with a S533A/D change indicated that this phosphorylation is not required for state transitions. Moreover, we also identified phosphorylation sites that are redox (state 2)-dependent but independent of Stt7 and additional phosphorylation sites that are redox-independent.The primary photochemical reactions of photosynthesis are catalyzed by the pigment-protein complexes photosystem II (PSII)1 and PSI (PSI), which are linked in series through the plastoquinone pool, the cytochrome b6f complex, and plastocyanin in the thylakoid membranes. Upon light absorption by the antenna systems of PSII and PSI, charge separations occur across the membrane that lead to the oxidation of water by PSII and electron flow to PSI and ultimately to the reduction of NADP+. Because the antenna systems of PSII and PSI have different pigment composition, they are differentially sensitized upon changes in light quality and quantity. However, photosynthetic organisms have the ability to adapt to changes in light. They balance energy input and consumption in the short term through dissipation of excess absorbed light energy into heat through non-photochemical quenching and regulate absorption of excitation energy between PSII and PSI through state transitions (supplemental Fig. 1). This reversible redistribution leads to an overall increase in photosynthetic quantum yield. State transitions occur when preferential excitation of PSII reduces the plastoquinone pool. This leads to the activation of a thylakoid protein kinase as a result of the docking of plastoquinol to the Qo site of the cytochrome b6f complex (1, 2) and to the phosphorylation of the polypeptides of the light-harvesting complex II (LHCII), a part of which migrates to PSI (state 2) (3–5). The process is reversible as preferential excitation of PSI inactivates the kinase and allows for dephosphorylation of LHCII and its return to PSII (state 1) (3, 6). In the green alga Chlamydomonas reinhardtii, the LHCII protein set consists of Type I (Lhcbm3, Lhcbm4, Lhcbm6, Lhcbm8, and Lhcbm9), Type II (Lhcbm5), Type III (Lhcbm2 and Lhcbm7), and Type IV (Lhcbm1 and Lhcbm10) proteins and of Lhcb7, CP26, and CP29 (7). Because of their nearly identical sequences and sizes, several of these Lhcbm proteins cannot be distinguished by SDS-PAGE. Most of them fractionate into four bands called P11 and P13 (Type I), P16 (Type IV), and P17 (Type III). Whereas P16 is not phosphorylated, phosphorylation events occur on P11, P13, and P17 (7, 8).The association of the mobile part of LHCII to PSI during a transition from state 1 to state 2 requires the PsaH subunit (9) and CP29, which also moves to PSI and is essential for docking LHCII to PSI (10–12). The lateral displacement of LHCII from the PSII-rich grana to the PSI-rich lamellar thylakoid regions results in transfer to PSI of about 80% of the excitation energy absorbed by LHCII in C. reinhardtii (13), a considerably higher amount than in land plants in which only 15–20% of LHCII is mobile (3). In C. reinhardtii, state transitions are associated with a reorganization of the photosynthetic electron transfer chain with a switch from linear to cyclic electron flow during a transition from state 1 to state 2 (14, 15). Thus, cells produce ATP and NADPH in state 1 but only ATP in state 2. It appears that the major function of state transitions in this alga is to adjust the level of ATP and the ATP/NADPH ratio to cellular demands (5).Thylakoid membranes contain appressed grana and nonappressed stromal domains in which PSII and PSI are enriched, respectively. Because LHCII is a major stabilizer of the grana structure (16), the movement of LHCII from PSII to PSI is expected to lead to major rearrangements of these membranes during state transitions. Indeed, based on extensive electron microscope studies, it was proposed that fusion and fission events occur at the interface between the grana and stroma lamellar domains that lead to a remodeling of the membranes (17).Mapping of in vivo protein phosphorylation sites in photosynthetic membranes of Chlamydomonas revealed a total of 19 sites corresponding to 15 genes (18). It was shown that the major changes are clustered at the interface between the PSII core and the associated LHCII proteins during state transitions. Phosphorylation of the PSII core subunits D2 and PsbR and multiple phosphorylations of the minor LHCII antenna subunit CP29 were detected as well as phosphorylation of Lhcbm1, which belongs to the major LHCII complex (18).Although the phosphorylation of LHCII was observed many years ago (6), it is only recently that kinases involved in this process were uncovered. Fleischmann et al. (19) and Kruse et al. (20) used a genetic approach in C. reinhardtii with the aim of dissecting the signal transduction chain of state transitions. Two allelic mutants blocked in state 1 were identified that are affected in the Stt7 gene encoding a thylakoid Ser-Thr protein kinase that is required for LHCII phosphorylation during a transition from state 1 to state 2 (21). This Stt7 kinase is conserved in land plants and has an ortholog, STN7, in Arabidopsis (22).The 754-amino acid Stt7 kinase has a catalytic domain characteristic of Ser-Thr kinases (21). It contains a putative 41-amino acid transit peptide at its N-terminal end, and the protein is localized on the thylakoid membrane. Stt7 is associated with photosynthetic complexes including LHCII, PSI, and the cytochrome b6f complex (23). Stt7 also contains a transmembrane region that separates its catalytic kinase domain on the stromal side from its N-terminal end in the thylakoid lumen with two conserved Cys residues that are critical for its activity and state transitions (23). Moreover, the level of Stt7 decreases considerably under state 1 conditions, and the kinase acts in catalytic amounts (23). However, it is not yet known whether this kinase directly phosphorylates LHCII or whether it is part of a kinase cascade involved in the signaling pathway of state transitions.In this work, we used a mass spectrometry-based approach (24) to map the in vivo Stt7-dependent protein phosphorylation sites within thylakoid membranes isolated from the green alga C. reinhardtii subjected to state 1 and state 2 conditions. In contrast with the earlier studies via direct MS/MS sequencing of the IMAC-enriched phosphorylated peptides from thylakoid proteins (18, 25), we performed additional LC-MS/MS-based analyses using alternating collision-induced dissociation and electron transfer dissociation of peptide ions. This approach revealed novel phosphorylation sites in LHCII polypeptides, in several other membrane and membrane-associated proteins, and in the thylakoid protein kinases Stt7 and Stl1, suggesting the existence of a thylakoid protein kinase cascade. Relative quantification of phosphorylated peptides labeled with stable isotopes determined the specific Stt7-dependent phosphorylation site in CP29 linker protein under state 2. Moreover, we also identified phosphorylation sites that are redox-dependent but independent of Stt7 and additional phosphorylation sites that are redox-independent. This mapping provides new insights into the regulatory network of protein phosphorylation in algal photosynthetic membranes during state transitions. 相似文献
16.
Marjaana Rantala Björn Lundin Eva‐Mari Aro 《The Plant journal : for cell and molecular biology》2016,87(5):484-494
STN7 kinase catalyzes the phosphorylation of the globally most common membrane proteins, the light‐harvesting complex II (LHCII) in plant chloroplasts. STN7 itself possesses one serine (Ser) and two threonine (Thr) phosphosites. We show that phosphorylation of the Thr residues protects STN7 against degradation in darkness, low light and red light, whereas increasing light intensity and far red illumination decrease phosphorylation and induce STN7 degradation. Ser phosphorylation, in turn, occurs under red and low intensity white light, coinciding with the client protein (LHCII) phosphorylation. Through analysis of the counteracting LHCII phosphatase mutant tap38/pph1, we show that Ser phosphorylation and activation of the STN7 kinase for subsequent LHCII phosphorylation are heavily affected by pre‐illumination conditions. Transitions between the three activity states of the STN7 kinase (deactivated in darkness and far red light, activated in low and red light, inhibited in high light) are shown to modulate the phosphorylation of the STN7 Ser and Thr residues independently of each other. Such dynamic regulation of STN7 kinase phosphorylation is crucial for plant growth and environmental acclimation. 相似文献
17.
The light reactions of photosynthesis in green plants are mediated by four large protein complexes, embedded in the thylakoid membrane of the chloroplast. Photosystem I (PSI) and Photosystem II (PSII) are both organized into large supercomplexes with variable amounts of membrane-bound peripheral antenna complexes. PSI consists of a monomeric core complex with single copies of four different LHCI proteins and has binding sites for additional LHCI and/or LHCII complexes. PSII supercomplexes are dimeric and contain usually two to four copies of trimeric LHCII complexes. These supercomplexes have a further tendency to associate into megacomplexes or into crystalline domains, of which several types have been characterized. Together with the specific lipid composition, the structural features of the main protein complexes of the thylakoid membranes form the main trigger for the segregation of PSII and LHCII from PSI and ATPase into stacked grana membranes. We suggest that the margins, the strongly folded regions of the membranes that connect the grana, are essentially protein-free, and that protein-protein interactions in the lumen also determine the shape of the grana. We also discuss which mechanisms determine the stacking of the thylakoid membranes and how the supramolecular organization of the pigment-protein complexes in the thylakoid membrane and their flexibility may play roles in various regulatory mechanisms of green plant photosynthesis. 相似文献
18.
Lorenzo Ferroni Martina Angeleri Laura Pantaleoni Cristina Pagliano Paolo Longoni Francesco Marsano Eva‐Mari Aro Marjaana Suorsa Costanza Baldisserotto Martina Giovanardi Rino Cella Simonetta Pancaldi 《The Plant journal : for cell and molecular biology》2014,77(6):893-905
Evolution of vascular plants required compromise between photosynthesis and photodamage. We analyzed representative species from two divergent lineages of vascular plants, lycophytes and euphyllophytes, with respect to the response of their photosynthesis and light‐harvesting properties to increasing light intensity. In the two analyzed lycophytes, Selaginella martensii and Lycopodium squarrosum, the medium phase of non‐photochemical quenching relaxation increased under high light compared to euphyllophytes. This was thought to be associated with the occurrence of a further thylakoid phosphoprotein in both lycophytes, in addition to D2, CP43 and Lhcb1‐2. This protein, which showed light intensity‐dependent reversible phosphorylation, was identified in S. martensii as Lhcb6, a minor LHCII antenna subunit of PSII. Lhcb6 is known to have evolved in the context of land colonization. In S. martensii, Lhcb6 was detected as a component of the free LHCII assemblies, but also associated with PSI. Most of the light‐induced changes affected the amount and phosphorylation of the LHCII assemblies, which possibly mediate PSI–PSII connectivity. We propose that Lhcb6 is involved in light energy management in lycophytes, participating in energy balance between PSI and PSII through a unique reversible phosphorylation, not yet observed in other land plants. 相似文献
19.
Jayendra Pandey Elsinraju Devadasu Deepak Saini Kunal Dhokne Sureshbabu Marriboina Agepati S. Raghavendra Rajagopal Subramanyam 《The Plant journal : for cell and molecular biology》2023,113(1):60-74
The effects of drought on photosynthesis have been extensively studied, whereas those on thylakoid organization are limited. We observed a significant decline in gas exchange parameters of pea (Pisum sativum) leaves under progressive drought stress. Chl a fluorescence kinetics revealed the reduction of photochemical efficiency of photosystem (PS)II and PSI. The non-photochemical quenching (NPQ) and the levels of PSII subunit PSBS increased. Furthermore, the light-harvesting complexes (LHCs) and some of the PSI and PSII core proteins were disassembled in drought conditions, whereas these complexes were reassociated during recovery. By contrast, the abundance of supercomplexes of PSII-LHCII and PSII dimer were reduced, whereas LHCII monomers increased following the change in the macro-organization of thylakoids. The stacks of thylakoids were loosely arranged in drought-affected plants, which could be attributed to changes in the supercomplexes of thylakoids. Severe drought stress caused a reduction of both LHCI and LHCII and a few reaction center proteins of PSI and PSII, indicating significant disorganization of the photosynthetic machinery. After 7 days of rewatering, plants recovered well, with restored chloroplast thylakoid structure and photosynthetic efficiency. The correlation of structural changes with leaf reactive oxygen species levels indicated that these changes were associated with the production of reactive oxygen species. 相似文献
20.
Nellaepalli S Mekala NR Zsiros O Mohanty P Subramanyam R 《Biochimica et biophysica acta》2011,1807(9):1177-1184
The effect of temperature on the photosynthetic machinery is crucial for the fundamental understanding of plant physiology and the bioengineering of heat-tolerant varieties. In our study, Arabidopsis thaliana was exposed to mild (40°C), short-term heat stress in the dark to evaluate the heat-triggered phosphorylation and migration of light harvesting complex (LHC) II in both wild-type (wt) and mutant lacking STN7 kinase. The 77K emission spectra revealed an increase in PSI relative to PSII emission similar to increases observed in light-induced state I to state II transitions in wt but not in stn7 mutant. Immunoblotting results indicated that the major LHCII was phosphorylated at threonine sites under heat stress in wt plants but not in the mutant. These results support the proposition that mild heat stress triggers state transitions in the dark similar to light-induced state transitions, which involve phosphorylation of LHCII by STN7 kinase. Pre-treatment of Arabidopsis leaves with inhibitor DBMIB, altered the extent of LHCII phosphorylation and PSI fluorescence emission suggests that activation of STN7 kinase may be dependent on Cyt b(6)/f under elevated temperatures in dark. Furthermore, fast Chl a transient of temperature-exposed leaves of wt showed a decrease in the F(v)/F(m) ratio due to both an increase in F(o) and a decrease in F(m). In summary, our findings indicate that a mild heat treatment (40°C) induces state transitions in the dark resulting in the migration of phosphorylated LHCII from the grana to the stroma region. 相似文献