In higher plants,stomatal movements represent a critical physiological process that matains cellular water homestasis while enabling photosynthetic gas exchange.Open stomata 1(OST1),a key protein kinase in the abscisi...In higher plants,stomatal movements represent a critical physiological process that matains cellular water homestasis while enabling photosynthetic gas exchange.Open stomata 1(OST1),a key protein kinase in the abscisic acid(ABA)signaling cascade,has been established as a central regulator of stomatal dynamics.This study reveals that two highly conserved mitogen-activated protein kinase 1(MAP4K1)and MAP4K2 are positive regulators in ABA promoted stomatal closure,and ABA-activated OST1 potentiates MAP4K1/2 through phosphorylation at conserved serine and threonine residues(S166,T170,and S479/S488).The activated MAP4K1,in turn,phosphorylates two critical downstream targets:plasma membrane H+-ATPase 2(AHA2)at residues T858,T881,and Y946,and slow anion channel-associated 1(SLAC1)at T114 and S116.Functional analysis demonstrates that the phosphomimetic(3D:S166D/T170D/S479D)MAP4K1,but not non-phosphorylatable(3A:S166A/T170A/S479A)MAP4K1,could fully restore drought tolerance and reduced water loss in detached leaves of map4k1map4k2 double mutant.Our findings delineate a previously unrecognized signaling module comprising OST1-MAP4K1/2-AHA2/SLAC1,which crucially modulates ABA-mediated stomatal regulation.This work advances our mechanistic understanding of phosphorylation cascades governing plant water relations and stress responses.展开更多
Plant hormone abscisic acid （ABA） serves as an integrator of environmental stresses such as drought to trig-ger stomatal closure by regulating specific ion channels in guard cells. We previously reported that SLAC1,...Plant hormone abscisic acid （ABA） serves as an integrator of environmental stresses such as drought to trig-ger stomatal closure by regulating specific ion channels in guard cells. We previously reported that SLAC1, an outward anion channel required for stomatal closure, was regulated via reversible protein phosphorylation events involving ABA signaling components, including protein phosphatase 2C members and a SnRK2-type kinase （OST1）. In this study, we reconstituted the ABA signaling pathway as a protein-protein interaction relay from the PYL/RCAR-type receptors, to the PP2C-SnRK2 phosphatase-kinase pairs, to the ion channel SLAC1. The ABA receptors interacted with and inhibited PP2C phosphatase activity against the SnRK2-type kinase, releasing active SnRK2 kinase to phosphorylate, and activate the SLAC1 channel, leading to reduced guard cell turgor and stomatal closure. Both yeast two-hybrid and bimolecular fluorescence complementation assays were used to verify the interactions among the components in the pathway. These biochemical assays demonstrated activity modifications of phosphatases and kinases by their interaction partners. The SLAC1 channel activity was used as an endpoint readout for the strength of the signaling pathway, depending on the presence of different combinations of signaling components. Further study using transgenic plants overexpressing one of the ABA receptors demonstrated that changing the relative level of interacting partners would change ABA sensitivity.展开更多
Plants absorb sunlight to power the photochem- ical reactions of photosynthesis, which can potentially damage the photosynthetic machinery. However, the mech- anism that protects chloroplasts from the damage remains u...Plants absorb sunlight to power the photochem- ical reactions of photosynthesis, which can potentially damage the photosynthetic machinery. However, the mech- anism that protects chloroplasts from the damage remains unclear. In this work, we demonstrated that rice （Oryza sativa L.） SLAC7 is a generally expressed membrane protein. Loss- of-function of SLAC7 caused continuous damage to the chloroplasts of mutant leaves under normal light conditions. Ion leakage indicators related to leaf damage such as H^O2 and abscisic acid levels were significantly higher in slac7-1 than in the wild type. Consistently, the photosynthesis efficiency and Fv/Fm ratio of slac7-1 were significantly decreased （similar to photoinhibition）. In response to chloroplast damage, slat7- 1 altered its leaf morphology （curled or fused leaf） by the synergy between plant hormones and transcriptional factors to decrease the absorption of light, suggesting that a photoprotection mechanism for chloroplast damage was activated in slac7-1. When grown in dark conditions, slac7-1 displayed a normal phenotype. 5LAC7 under the control of the AtSLAC1 promoter could partially complement thephenotypes of Arabidopsis slacl mutants, indicating a partial conservation of SLAC protein functions. These results suggest that SLAC7 is essential for maintaining the chloroplast stability in rice.展开更多
基金supported by grants from the National Science Foundation of China(31921001)the Beijing Outstanding University Discipline。
文摘In higher plants,stomatal movements represent a critical physiological process that matains cellular water homestasis while enabling photosynthetic gas exchange.Open stomata 1(OST1),a key protein kinase in the abscisic acid(ABA)signaling cascade,has been established as a central regulator of stomatal dynamics.This study reveals that two highly conserved mitogen-activated protein kinase 1(MAP4K1)and MAP4K2 are positive regulators in ABA promoted stomatal closure,and ABA-activated OST1 potentiates MAP4K1/2 through phosphorylation at conserved serine and threonine residues(S166,T170,and S479/S488).The activated MAP4K1,in turn,phosphorylates two critical downstream targets:plasma membrane H+-ATPase 2(AHA2)at residues T858,T881,and Y946,and slow anion channel-associated 1(SLAC1)at T114 and S116.Functional analysis demonstrates that the phosphomimetic(3D:S166D/T170D/S479D)MAP4K1,but not non-phosphorylatable(3A:S166A/T170A/S479A)MAP4K1,could fully restore drought tolerance and reduced water loss in detached leaves of map4k1map4k2 double mutant.Our findings delineate a previously unrecognized signaling module comprising OST1-MAP4K1/2-AHA2/SLAC1,which crucially modulates ABA-mediated stomatal regulation.This work advances our mechanistic understanding of phosphorylation cascades governing plant water relations and stress responses.
基金a grant from the Biogreen21 Program (PJ008222) Rural Development Administration and the Research Foundation of Korea (NFR) grant funded by the Korea government (No.2011-0007600)，the US National Science Foundation and Korean WCU Program of National Research Foundation (to S.L.).No conflict of interest declared
文摘Plant hormone abscisic acid （ABA） serves as an integrator of environmental stresses such as drought to trig-ger stomatal closure by regulating specific ion channels in guard cells. We previously reported that SLAC1, an outward anion channel required for stomatal closure, was regulated via reversible protein phosphorylation events involving ABA signaling components, including protein phosphatase 2C members and a SnRK2-type kinase （OST1）. In this study, we reconstituted the ABA signaling pathway as a protein-protein interaction relay from the PYL/RCAR-type receptors, to the PP2C-SnRK2 phosphatase-kinase pairs, to the ion channel SLAC1. The ABA receptors interacted with and inhibited PP2C phosphatase activity against the SnRK2-type kinase, releasing active SnRK2 kinase to phosphorylate, and activate the SLAC1 channel, leading to reduced guard cell turgor and stomatal closure. Both yeast two-hybrid and bimolecular fluorescence complementation assays were used to verify the interactions among the components in the pathway. These biochemical assays demonstrated activity modifications of phosphatases and kinases by their interaction partners. The SLAC1 channel activity was used as an endpoint readout for the strength of the signaling pathway, depending on the presence of different combinations of signaling components. Further study using transgenic plants overexpressing one of the ABA receptors demonstrated that changing the relative level of interacting partners would change ABA sensitivity.
基金funded by the National High Technology Research and Development Program of China (863 Program)the National Program of Transgenic Variety Development of Chinathe National Natural Science Foundation of China
文摘Plants absorb sunlight to power the photochem- ical reactions of photosynthesis, which can potentially damage the photosynthetic machinery. However, the mech- anism that protects chloroplasts from the damage remains unclear. In this work, we demonstrated that rice （Oryza sativa L.） SLAC7 is a generally expressed membrane protein. Loss- of-function of SLAC7 caused continuous damage to the chloroplasts of mutant leaves under normal light conditions. Ion leakage indicators related to leaf damage such as H^O2 and abscisic acid levels were significantly higher in slac7-1 than in the wild type. Consistently, the photosynthesis efficiency and Fv/Fm ratio of slac7-1 were significantly decreased （similar to photoinhibition）. In response to chloroplast damage, slat7- 1 altered its leaf morphology （curled or fused leaf） by the synergy between plant hormones and transcriptional factors to decrease the absorption of light, suggesting that a photoprotection mechanism for chloroplast damage was activated in slac7-1. When grown in dark conditions, slac7-1 displayed a normal phenotype. 5LAC7 under the control of the AtSLAC1 promoter could partially complement thephenotypes of Arabidopsis slacl mutants, indicating a partial conservation of SLAC protein functions. These results suggest that SLAC7 is essential for maintaining the chloroplast stability in rice.
