Pepper protein phosphatase type 2C,CaADIP1 and its interacting partner CaRLP1 antagonistically regulate ABA signalling and drought response

Abscisic acid (ABA) is a key phytohormone that regulates plant growth and developmental processes, including seed germination and stomatal closing. Here, we report the identification and functional characterization of a novel type 2C protein phosphatase, CaADIP1 (Capsicum annuum A BA and D rought‐I nduced P rotein phosphatase 1). The expression of CaADIP1 was induced in pepper leaves by ABA, drought and NaCl treatments. Arabidopsis plants overexpressing CaADIP1 (CaADIP1‐OX) exhibited an ABA‐hyposensitive and drought‐susceptible phenotype. We used a yeast two‐hybrid screening assay to identify CaRLP1 (Capsicum annuum R CAR‐L ike P rotein 1), which interacts with CaADIP1 in the cytoplasm and nucleus. In contrast to CaADIP1‐OX plants, CaRLP1‐OX plants displayed an ABA‐hypersensitive and drought‐tolerant phenotype, which was characterized by low levels of transpirational water loss and increased expression of stress‐responsive genes relative to those of wild‐type plants. In CaADIP1‐OX/CaRLP1‐OX double transgenic plants, ectopic expression of the CaRLP1 gene led to strong suppression of CaADIP1‐induced ABA hyposensitivity during the germinative and post‐germinative stages, indicating that CaADIP1 and CaRLP1 act in the same signalling pathway and CaADIP1 functions downstream of CaRLP1. Our results indicate that CaADIP1 and its interacting partner CaRLP1 antagonistically regulate the ABA‐dependent defense signalling response to drought stress.     

A DEAD‐box RNA helicase,RH8, is critical for regulation of ABA signalling and the drought stress response via inhibition of PP2CA activity

Abscisic acid (ABA) is major plant hormone involved in regulating abiotic stress responses. Several studies have established that an ABA‐signalling transduction pathway—from ABA perception to response—functions in plant cells. The group A PP2Cs constitute core components of ABA signalling, and they negatively regulate ABA signalling and stress responses. Recent studies have identified and functionally analysed regulators of PP2C activity; however, the precise regulatory mechanisms remain unclear. In the present study, we used a yeast 2‐hybrid (Y2H) screening analysis to identify the DEAD‐box RNA helicase RH8, which interacted with PP2CA in the nucleus. rh8 knockout mutants exhibited ABA hyposensitivity and drought‐susceptible phenotypes characterized by high levels of transpirational water loss via reduced stomatal closure and decreased leaf temperatures. However, rh8/pp2ca double mutants showed ABA hypersensitivity and drought‐tolerant phenotypes, indicating that RH8 and PP2CA function in the same ABA‐signalling pathway in the drought stress response; moreover, RH8 functions upstream of PP2CA. In vitro phosphatase and kinase assays revealed that RH8 inhibits PP2CA phosphatase activity. Our data indicate that RH8 and its interacting partner PP2CA modulate the drought stress response via ABA‐dependent signalling.     

The pepper late embryogenesis abundant protein CaLEA1 acts in regulating abscisic acid signaling,drought and salt stress response

As sessile organisms, plants are constantly challenged by environmental stresses, including drought and high salinity. Among the various abiotic stresses, osmotic stress is one of the most important factors for growth and significantly reduces crop productivity in agriculture. Here, we report a function of the CaLEA1 protein in the defense responses of plants to osmotic stress. Our analyses showed that the CaLEA1 gene was strongly induced in pepper leaves exposed to drought and increased salinity. Furthermore, we determined that the CaLEA1 protein has a late embryogenesis abundant (LEA)_3 homolog domain highly conserved among other known group 5 LEA proteins and is localized in the processing body. We generated CaLEA1‐silenced peppers and CaLEA1‐overexpressing (OX) transgenic Arabidopsis plants to evaluate their responses to dehydration and high salinity. Virus‐induced gene silencing of CaLEA1 in pepper plants conferred enhanced sensitivity to drought and salt stresses, which was accompanied by high levels of lipid peroxidation in dehydrated and NaCl‐treated leaves. CaLEA1‐OX plants exhibited enhanced sensitivity to abscisic acid (ABA) during seed germination and in the seedling stage; furthermore, these plants were more tolerant to drought and salt stress than the wild‐type plants because of enhanced stomatal closure and increased expression of stress‐responsive genes. Collectively, our data suggest that CaLEA1 positively regulates drought and salinity tolerance through ABA‐mediated cell signaling.     

Identification and functional roles of CaDIN1 in abscisic acid signaling and drought sensitivity

Plants frequently face challenges caused by various abiotic stresses, including drought, and have evolved defense mechanisms to counteract the deleterious effects of these stresses. The phytohormone abscisic acid (ABA) is involved in signal transduction pathways that mediate defense responses of plants to abiotic stress. Here, we report a new function of the CaDIN1 protein in defense responses to abiotic stress. The CaDIN1 gene was strongly induced in pepper leaves exposed to ABA, NaCl, and drought stresses. CaDIN1 proteins share high sequence homology with other known DIN1 proteins and are localized in chloroplasts. We generated CaDIN1-silenced peppers and overexpressing transgenic Arabidopsis plants and evaluated their response to ABA and drought stress. Virus-induced gene silencing of CaDIN1 in pepper plants conferred enhanced tolerance to drought stress, which was accompanied by low levels of lipid peroxidation in dehydrated leaves. CaDIN1-overexpressing transgenic plants exhibited reduced sensitivity to ABA during seed germination and seedling stages. Transgenic plants were more vulnerable to drought than that by the wild-type plants because of decreased expression of ABA responsive stress-related genes and reduced stomatal closure in response to ABA. Together, these results suggest that CaDIN1 modulates drought sensitivity through ABA-mediated cell signaling.     

The role of Arabidopsis thaliana RASD1 gene in ABA‐dependent abiotic stress response

• Abiotic stress is one of the key parameters affecting plant productivity. Drought and soil salinity, in particular, challenge plants to activate various response mechanisms to withstand these adverse growth conditions. While the molecular events that take place are complex and to a large extent unclear, the plant hormone abscisic acid (ABA) is considered a major player in mediating the adaptation of plants to stress.
• Here we report the identification of an ABA‐insensitive mutant from Arabidopsis thaliana. A combination of molecular, genetic and physiology approaches were implemented, to characterise the AtRASD1 locus (A BA D ROUGHT 相似文献   

Abscisic acid is involved in phenolic compounds biosynthesis,mainly anthocyanins,in leaves of Aristotelia chilensis plants (Mol.) subjected to drought stress

Abscisic acid (ABA) regulates the physiological and biochemical mechanisms required to tolerate drought stress, which is considered as an important abiotic stress. It has been postulated that ABA might be involved in regulation of plant phenolic compounds biosynthesis, especially anthocyanins that accumulate in plants subjected to drought stress; however, the evidence for this postulate remains elusive. Therefore, we studied whether ABA is involved in phenolic compounds accumulation, especially anthocyanin biosynthesis, using drought stressed Aristotelia chilensis plants, an endemic berry in Chile. Our approach was to use fluridone, an ABA biosynthesis inhibitor, and then subsequent ABA applications to young and fully‐expanded leaves of drought stressed A. chilensis plants during 24, 48 and 72 h of the experiment. Plants were harvested and leaves were collected separately to determine the biochemical status. We observed that fluridone treatments significantly decreased ABA concentrations and total anthocyanin (TA) concentrations in stressed plants, including both young and fully‐expanded leaves. TA concentrations following fluridone treatment were reduced around fivefold, reaching control plant levels. ABA application restored ABA levels as well as TA concentrations in stressed plant at 48 h of the experiment. We also observed that TA concentrations followed the same pattern as ABA concentrations in the ABA treated plants. Quantitative real‐time PCR revealed that AcUFGT gene expression decreased in fully‐expanded leaves of stressed plants treated with fluridone, while a subsequent ABA application increased AcUFGT expression. Taken together, our results suggest that ABA is involved in the regulation of anthocyanin biosynthesis under drought stress.     

PeCHYR1, a ubiquitin E3 ligase from Populus euphratica,enhances drought tolerance via ABA‐induced stomatal closure by ROS production in Populus

Drought, a primary abiotic stress, seriously affects plant growth and productivity. Stomata play a vital role in regulating gas exchange and drought adaptation. However, limited knowledge exists of the molecular mechanisms underlying stomatal movement in trees. Here, PeCHYR1, a ubiquitin E3 ligase, was isolated from Populus euphratica, a model of stress adaptation in forest trees. PeCHYR1 was preferentially expressed in young leaves and was significantly induced by ABA (abscisic acid) and dehydration treatments. To study the potential biological functions of PeCHYR1, transgenic poplar 84K (Populus alba × Populus glandulosa) plants overexpressing PeCHYR1 were generated. PeCHYR1 overexpression significantly enhanced H₂O₂ production and reduced stomatal aperture. Transgenic lines exhibited increased sensitivity to exogenous ABA and greater drought tolerance than that of WT (wild‐type) controls. Moreover, up‐regulation of PeCHYR1 promoted stomatal closure and decreased transpiration, resulting in strongly elevated WUE (water use efficiency). When exposed to drought stress, transgenic poplar maintained higher photosynthetic activity and biomass accumulation. Taken together, these results suggest that PeCHYR1 plays a crucial role in enhancing drought tolerance via ABA‐induced stomatal closure caused by hydrogen peroxide (H₂O₂) production in transgenic poplar plants.     

Open stomata 1 (OST1) kinase controls R–type anion channel QUAC1 in Arabidopsis guard cells

Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell S–type anion channel SLAC1. Arabidopsis ABI1 and OST1 loss‐of‐function mutants are characterized by an extreme wilting 'open stomata′ phenotype. Given the fact that guard cells express both SLAC‐ and R–/QUAC‐type anion channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 channel. In other words, are ABI1/OST1 defects preventing both of the guard cell anion channel types from operating properly in terms of stomatal closure? The activation of the R–/QUAC‐type anion channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell‐free background of Xenopus oocytes. Patch‐clamp studies on guard cells show that ABA activates R–/QUAC‐type currents of wild‐type plants, but to a much lesser extent in those of abi1–1 and ost1–2 mutants. In the oocyte system the co‐expression of QUAC1 and OST1 resulted in a pronounced activation of the R–type anion channel. These studies indicate that OST1 is addressing both S–/SLAC‐ and R–/QUAC‐type guard cell anion channels, and explain why the ost1–2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.     

Knockout of AtDjB1, a J‐domain protein from Arabidopsis thaliana,alters plant responses to osmotic stress and abscisic acid

AtDjB1 is a member of the Arabidopsis thaliana J‐protein family. AtDjB1 is targeted to the mitochondria and plays a crucial role in A. thaliana heat and oxidative stress resistance. Herein, the role of AtDjB1 in adapting to saline and drought stress was studied in A. thaliana. AtDjB1 expression was induced through salinity, dehydration and abscisic acid (ABA) in young seedlings. Reverse genetic analyses indicate that AtDjB1 is a negative regulator in plant osmotic stress tolerance. Further, AtDjB1 knockout mutant plants (atj1‐1) exhibited greater ABA sensitivity compared with the wild‐type (WT) plants and the mutant lines with a rescued AtDjB1 gene. AtDjB1 gene knockout also altered the expression of several ABA‐responsive genes, which suggests that AtDjB1 is involved in osmotic stress tolerance through its effects on ABA signaling pathways. Moreover, atj1‐1 plants exhibited higher glucose levels and greater glucose sensitivity in the post‐germination development stage. Applying glucose promoted an ABA response in seedlings, and the promotion was more evident in atj1‐1 than WT seedlings. Taken together, higher glucose levels in atj1‐1 plants are likely responsible for the greater ABA sensitivity and increased osmotic stress tolerance.