Pollen-expressed F-box gene family and mechanism of S-RNase-based gametophytic self-incompatibility (GSI) in Rosaceae

Many species of Rosaceae, Solanaceae, and Plantaginaceae exhibit S-RNase-based self-incompatibility (SI) in which pistil-part specificity is controlled by S locus-encoded ribonuclease (S-RNase). Although recent findings revealed that S locus-encoded F-box protein, SLF/SFB, determines pollen-part specificity, how these pistil- and pollen-part S locus products interact in vivo and elicit the SI reaction is largely unclear. Furthermore, genetic studies suggested that pollen S function can differ among species. In Solanaceae and the rosaceous subfamily Maloideae (e.g., apple and pear), the coexistence of two different pollen S alleles in a pollen breaks down SI of the pollen, a phenomenon known as competitive interaction. However, competitive interaction seems not to occur in the subfamily Prunoideae (e.g., cherry and almond) of Rosaceae. Furthermore, the effect of the deletion of pollen S seems to vary among taxa. This review focuses on the potential differences in pollen-part function between subfamilies of Rosaceae, Maloideae, and Prunoideae, and discusses implications for the mechanistic divergence of the S-RNase-based SI.     

The speed of intracellular signal transfer for chloroplast movement

The photoreceptors for chloroplast photorelocation movement have been known, but the signal(s) raised by photoreceptors remains unknown. To know the properties of the signal(s) for chloroplast accumulation movement, we examined the speed of signal transferred from light-irradiated area to chloroplasts in gametophytes of Adiantum capillus-veneris. When dark-adapted gametophyte cells were irradiated with a microbeam of various light intensities of red or blue light for 1 min or continuously, the chloroplasts started to move towards the irradiated area. The speed of signal transfer was calculated from the relationship between the timing of start moving and the distance of chloroplasts from the microbeam and was found to be constant at any light conditions. In prothallial cells, the speed was about 1.0 µm min⁻¹ and in protonemal cells about 0.7 µm min⁻¹ towards base and about 2.3 µm min⁻¹ towards the apex. We confirmed the speed of signal transfer in Arabidopsis thaliana mesophyll cells under continuous irradiation of blue light, as was about 0.8 µm min⁻¹. Possible candidates of the signal are discussed depending on the speed of signal transfer.Key words: Adiantum capillus-veneris, Arabidopsis thaliana, blue light, chloroplast movement, microbeam, red light, signalOrganelle movement is essential for plant growth and development and tightly regulated by environmental conditions.¹ It is well known that light regulates chloroplast movement in various plant species. Chloroplast movement can be separated into three categories, (1) photoperception by photoreceptors, (2) signal transduction from photoreceptor to chloroplasts and (3) movement of chloroplasts and has been analyzed from a physiological point of view.² We recently identified the photoreceptors in Arabidopsis thaliana, fern Adiantum capillus-veneris, and moss Physcomitrella patens. In A. thaliana, phototropin 2 (phot2) mediates the avoidance movement,^3,4 whereas both phototropin 1 (phot1) and phot2 mediate the accumulation response.⁵ A chimeric photoreceptor neochrome 1 (neo1)⁶ was identified as a red/far-red and blue light receptor that mediates red as well as blue light-induced chloroplast movement in A. capillusveneris.⁷ Interestingly, neo1 mediated red and blue light-induced nuclear movement and negative phototropic response of A. capillus-veneris rhizoid cells.^8,9 On the mechanism of chloroplast movement, we also found a novel structure of actin filaments that appeared between chloroplast and the plasma membrane at the front side of moving chloroplast.¹⁰ Recent studies using the technique of microbeam irradiation have revealed that chloroplasts do not have a polarity for light-induced accumulation movement and can move freely in any direction both in A. capillus-veneris prothallial cells and in A. thaliana mesophyll cells.¹¹ However, the signal that may be released from photoreceptors and transferred to chloroplasts remains unknown.To understand the properties of the signal for the chloroplast accumulation response, we examined the speed of signal transfer in dark-adapted A. capillus-veneris gametophyte cells and A. thaliana mesophyll cells by partial cell irradiation with a red and/or blue microbeam of various light intensities for 1 min and the following continuous irradiation, respectively.¹²As shown in Figure 1, the relation between the distance of chloroplasts from the microbeam and the timing when each chloroplast started moving toward the microbeam irradiated area (shown as black dots in Fig. 1) was obtained and plotted. The lag time between the onset of microbeam irradiation and the timing of start moving of chloroplasts is the time period needed for a signal to reach each chloroplast. To obtain more accurate data many chloroplasts at various positions were used. The slope of the approximate line indicates the average speed of the signal transfer. Shown with a protonemal cell at the left side of this figure is an instance where the speed of signal transfer from basal-to-apical (acropetal) direction is obtained.Open in a separate windowFigure 1How to calculate the speed of signal transfer in the basal cell of two-celled protonema of Adiantum capillus-veneris. The relationship between the distance of chloroplast position from the edge of the microbeam to the center of each chloroplast as shown in left side of figure and the timing of chloroplast movement initiated shown as the black dots was obtained. Inclination of the approximate lines connecting dots indicates the speeds of the signal transfer.In protonemal cells, which are tip-growing linear cells, the average speed of signal transfer was about 2.3 µm min⁻¹ from basal-to-apical (acropetal) and about 0.7 µm min⁻¹ from apical-to-basal (basipetal) directions. These values were almost constant irrespective of light intensity, wavelength, irradiation period, and the region of the cell irradiated.¹² The difference of speed between basipetal and acropetal directions may be depending on cell polarity. The signal transfer in prothallial cells of A. capillus-veneris and mesophyll cells of A. thaliana was about 1.0 µm min⁻¹ to any direction, probably because they may not have a polarity comparing to protonemal cells or have a weak polarity if any. Thus, the speed of signal transfer must be conserved in most land plants,¹² if not influenced by strong polarity.

Differential expression of ACC oxidase genes during low-pH-induced root hair formation in lettuce (<Emphasis Type="Italic">Lactuca sativa</Emphasis> L.) seedlings

Root hair formation is induced in lettuce seedlings when the seedlings are transferred from a liquid medium at pH 6.0 to one at pH 4.0. Auxin, ethylene, and light are also required for the induction of root hair formation. To investigate the mechanism by which ethylene production is regulated during root hair formation, we isolated three 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase genes (Ls-ACO1, 2, and 3) from lettuce, each of which exists as a single copy in the genome. Analysis of the deduced amino acid sequences of the three ACO proteins as well as a phylogenetic analysis revealed that Ls-ACO3 was the most divergent among the ACO family. Northern hybridization analyses revealed that the mRNA levels of Ls-ACO2, but not Ls-ACO1 and Ls-ACO3, increased in the primary root after the transfer to a pH 4.0 medium. Addition of ACC or indole-3-acetic acid (IAA) to the pH 6.0 medium induced root hair formation, and a concomitant accumulation of Ls-ACO2 mRNA was observed. In contrast, the mRNA levels of Ls-ACO1 and Ls-ACO3 were unaffected by either ACC or IAA treatment. Furthermore, white light irradiation of dark-grown seedlings following the transfer to pH 4.0 medium induced the accumulation of all three ACO mRNAs. However, accumulation of Ls-ACO2 mRNA was also observed in non-irradiated seedlings, suggesting that the expression of Ls-ACO2 was induced not by light but by low pH. These results suggest that among the differentially regulated ACO genes, Ls-ACO2 plays a key role in ethylene production during low-pH-induced root hair formation in lettuce.     

Psb30 contributes to structurally stabilise the Photosystem II complex in the thermophilic cyanobacterium Thermosynechococcus elongatus

A deletion mutant that lacks the Psb30 protein, one of the small subunits of Photosystem II, was constructed in a Thermosynechococcus elongatus strain in which the D1 protein is expressed from the psbA₃ gene (WT*). The ΔPsb30 mutant appears more susceptible to photodamage, has a cytochrome b₅₅₉ that is converted into the low potential form, and probably also lacks the PsbY subunit. In the presence of an inhibitor of protein synthesis, the ?Psb30 lost more rapidly the water oxidation function than the WT* under the high light conditions. These results suggest that Psb30 contributes to structurally and functionally stabilise the Photosystem II complex in preventing the conversion of cytochrome b₅₅₉ into the low potential form. Structural reasons for such effects are discussed.     

Pdk1 kinase regulates basal disease resistance through the OsOxi1-OsPti1a phosphorylation cascade in rice

The AGC kinase OsOxi1, which has been isolated as an interactor with OsPti1a, positively regulates basal disease resistance in rice. In eukaryotes, AGC kinase family proteins are regulated by 3-phosphoinositide-dependent protein kinase 1 (Pdk1). In Arabidopsis, AtPdk1 directly interacts with phosphatidic acid, which functions as a second messenger in both biotic and abiotic stress responses. However, the functions of Pdk1 are poorly understood in plants. We show here that OsPdk1 acts upstream of the OsOxi1-OsPti1a signal cascade in disease resistance in rice. OsPdk1 interacts with OsOxi1 and phosphorylates the Ser283 residue of OsOxi1 in vitro. To investigate whether OsPdk1 is involved in immunity that is triggered by microbial-associated molecular patterns, we analyzed the phosphorylation status of OsPdk1 in response to chitin elicitor. Like OsOxi1, OsPdk1 is rapidly phosphorylated in response to chitin elicitor, suggesting that OsPdk1 participates in signal transduction through pathogen recognition. The overexpression of OsPdk1 enhanced basal resistance against a blast fungus, Magnaporthe oryzae, and a bacterial pathogen, Xanthomonas oryzae pv. oryzae (Xoo). Taken together, these results suggest that OsPdk1 positively regulates basal disease resistance through the OsOxi1-OsPti1a phosphorylation cascade in rice.     

White clover living mulch increases the yield of silage corn via arbuscular mycorrhizal fungus colonization

A field experiment was conducted to investigate the effects of white clover living mulch on the arbuscular mycorrhizal (AM) fungus colonization of corn roots and the yield of silage corn. The following seven treatments were setup in a field that had been kept bare by rotary tillage from August 2003 to July 2004: two white clover living mulch treatments without phosphorus (P) application, with the white clover shoots clipped and removed or allowed to lie in place before sowing corn; one no-tillage treatment without P application; and four rotary tillage treatments with different P application rates. White clover was broadcasted in the living mulch treatments in August 2004. In June 2005, the white clover shoots in the living mulch treatments were clipped. After tilling the four rotary tillage treatments, corn was sown in all the treatments. The fallow period before sowing corn was 0 month (living mulch treatments) and 22 months (no-tillage and rotary tillage treatments). At knee high stage, the AM fungus colonization of the corn roots and the P concentrations of the corn shoots in both the living mulch treatments were increased relative to those in the other treatments. The yield of corn tended to increase in the no-tillage and rotary tillage treatments with an increase in the P application rate. On the other hand, the yields of corn in the living mulch treatments without the P application were not significantly different from the maximum yield among the no-tillage and rotary tillage treatments. These results suggested that the white clover living mulch increased the yield of corn by facilitating the AM fungus colonization and improving the P nutrition of corn.     

Protein kinase C delta regulates the phosphorylation of heat shock protein 27 in human hepatocellular carcinoma

We have recently reported that attenuated phosphorylation of heat shock protein (HSP) 27 correlates with tumor progression in patients with hepatocellular carcinoma (HCC). In the present study, we investigated what kind of kinase regulates phosphorylation of HSP27 in human HCC-derived HuH7 cells. 12-O-tetradecanoylphorbol-13-acetate (TPA) and 1-oleoyl-2-acetylglycerol, direct activators of protein kinase C (PKC), markedly strengthened the phosphorylation of HSP27. Bisindorylmaleimide I, an inhibitor of PKC, suppressed the TPA-induced levels of HSP27 phosphorylation in addition to its basal levels. Knock down of PKCdelta suppressed HSP27 phosphorylation, as well as p38 mitogen-activated protein kinase (MAPK) phosphorylation. SB203580, an inhibitor of p38 MAPK, suppressed the TPA-induced HSP27 phosphorylation. Our results strongly suggest that activation of PKCdelta regulates the phosphorylation of HSP27 via p38 MAPK in human HCC.     

Important role of apoptosis signal-regulating kinase 1 in ischemic acute kidney injury

We investigated the role of apoptosis signal-regulating kinase 1 (ASK1) in ischemia/reperfusion (I/R)-induced acute kidney injury (AKI). Blood urea nitrogen (BUN) and serum creatinine were significantly higher in ASK1+/+ mice than in ASK1−/− mice after I/R injury. Renal histology of ASK1+/+ mice showed significantly greater tubular necrosis and degradation. In ASK1−/− mice, phosphorylation of ASK1, JNK, and p38K, and the number of TUNEL-positive cells and infiltrated leukocytes decreased after I/R injury. Apoptotic changes were significantly decreased in cultured renal tubular epithelial cells (TECs) from ASK1−/− mice under hypoxic condition. Transfection with dominant-active ASK1 induced apoptosis in TECs. Protein expression of monocyte chemoattractant protein-1 (MCP-1) was significantly weaker in ASK1−/− mice after I/R injury. Transfection with dominant negative-ASK1 significantly decreased MCP-1 production in TECs. These results demonstrated that ASK1 is activated in I/R-induced AKI, and blockage of ASK1 attenuates renal tubular apoptosis, MCP-1 expression, and renal function.     

Action of neltenexine on anion secretion in human airway epithelia

Neltenexine has been applied to human lung diseases such as chronic obstructive pulmonary disease (COPD) as a mucolytic agent. However, we have no information on the neltenexine action in bronchial epithelial cells. We studied the neltenexine action on the ion transport in human submucosal serous Calu-3 cells. Under a hyper-secreting condition caused by terbutaline (a beta2-adrenergic agonist), neltenexine diminished anion secretion by inhibiting the Cl- and HCO3- uptake via Na+/K+/2Cl- cotransporter and Na+/HCO3- cotransporter without blockade of the cystic fibrosis transmembrane conductance regulator (CFTR) channel, and also diminished anion secretion via stimulation of Cl-/HCO3- exchanger, which facilitates the extrusion of more CFTR-permeant anion, Cl-, with the uptake of less CFTR-permeant anion, HCO3-. Thus, neltenexine reduced the hyper-secretion to keep an appropriate fluid level in the airway, providing a possibility that neltenexine can be an effective drug in airway obstructive diseases by decreasing the airway resistance under a hyper-secreting condition.