Nitric oxide and hydrogen sulfide share regulatory functions in higher plant events

Nitric oxide(NO)and hydrogen sulfide(HS)are two molecules that share signaling properties in plant and animal cells NO and H2S originate two farmilies of de rived mol ecules designated reactive nitrogen and sulfur species(RNS and RSS,respectively).These molecules are responsible for certain protein regulatory processes through posttranslational modifications(PTMs),being the most remarkable S nitrosation and persufidation,which afect the thiol group of cysteine residues.NO and H2S can also exert regulatory functions due to their interaction through the iron present in proteins that contain heme groups or iron-sulfur dlusters,as reported mainly in animal cells.Howewer,the available information in plant cells is still very limited thus far.In higher plants,NO and H2S are involved in a myriad of physiological events from seed germination to fruit ripening,but also the mec hanism of response to biotic and abiotic stress conditions.This vie wpoint manuscript highlights the functional regulatory parllelism of these two molecules which also interact with the metabolism of reactive oxygen species(ROS)in plant cells.

Hydrogen Sulfide Positively Regulates Abscisic Acid Signaling through Persulf idation of SnRK2.6 in Guard Cells

The phytohormone abscisic acid(ABA)plays pivotal roles in triggering stomatal closure and facilitating adaptation of plants to drought stress.Hydrogen sulfide(H2S),a small signaling gas molecule,is involved in ABA-dependent stomatal closure.However,how H2S regulates ABA signaling remains largely unclear.Here,we show that ABA induces the production of H2S catalyzed by L-CYSTEINE DESULFHYDRASE1(DES1)in guard cells,and H2S in turn positively regulates ABA signaling through persulfidation of Open Stomata 1(OST1)/SNF1-RELATED PROTEIN KINASE2.6(SnRK2.6).Two cysteine(Cys)sites,Cys131 and Cys137,which are exposed on the surface of SnRK2.6 and close to the activation loop,were identified to be persulfidated,which promotes the activity of SnRK2.6 and its interaction with ABA response element-binding factor 2(ABF2),a transcription factor acting downstream of ABA signaling.When Cys131,Cys137,or both residues in SnRK2.6 were substituted with serine(S),H2S_induced SnRK2_6 activity and SnRK2.6-ABF2 interaction were partially(SnRK2.6c131s and SnRK2.6c137S)or completely(SnRK2.6c131sc137S)compromised.Introduction of SnRK2.6c131s,SnRK2.6c137S,or SnRK2.6c131sc137S into the ost1-3 mutant could not rescue the mutant phenotype:less sensitivity to ABA-and H2S-induced stomatal closure and Ca2+influx as well as increased water loss and decreased drought tolerance.Taken together,our study reveals a novel post-translational regulatory mechanism of ABA signaling whereby H2S persulfidates SnRK2.6 to promote ABA signaling and ABA-induced stomatal closure.

Hydrogen sulfide, a signaling molecule in plant stress responses

Gaseous molecules, such as hydrogen sulfide(H_2S)and nitric oxide(NO), are crucial players in cellular and(patho)physiological processes in biological systems. The biological functions of these gaseous molecules, which were first discovered and identified as gasotransmitters in animals, have received unprecedented attention from plant scientists in recent decades. Researchers have arrived at the consensus that H_2S is synthesized endogenously and serves as a signaling molecule throughout the plant life cycle.However, the mechanisms of H_2S action in redox biology is still largely unexplored. This review highlights what we currently know about the characteristics and biosynthesis of H_2S in plants. Additionally,we summarize the role of H_2S in plant resistance to abiotic stress. Moreover, we propose and discuss possible redox-dependent mechanisms by which H_2S regulates plant physiology.

Hydrogen sulfide-linked persulfidation of ABI4 controls ABA responses through the transactivation of MAPKKK18 in Arabidopsis

Hydrogen sulfide(H2S)is a signaling molecule that regulates plant hormone and stress responses.The phytohormone abscisic acid(ABA)plays an important role in plant adaptation to unfavorable environmental conditions and induces the persulfidation of L-CYSTEINE DESULFHYDRASE1(DES1)and the production of H2S in guard cells.However,it remains largely unclear how H2S and protein persulfidation participate in the relay of ABA signals.In this study,we discovered that ABSCISIC ACID INSENSITIVE 4(ABI4)acts downstream of DES1 in the control of ABA responses in Arabidopsis.ABI4 undergoes persulfidation at Cys250 that is triggered in a time-dependent manner by ABA,and loss of DES1 function impairs this process.Cys250 and its persulfidation are essential for ABI4 function in the regulation of plant responses to ABA and the H2S donor NaHS during germination,seedling establishment,and stomatal closure,which are abolished in the ABI4Cys250Ala mutated variant.Introduction of the ABI4Cys250Ala variant into the abi4 des1 mutant did not rescue its hyposensitivity to ABA.Cys250 is critical for the binding of ABI4 to its cognate motif in the promoter of Mitogen-Activated Protein Kinase Kinase Kinase 18(MAPKKK18),which propagates the MAPK signaling cascade induced by ABA.Furthermore,the DES1-mediated persulfidation of ABI4 enhances the transactivation activity of ABI4 toward MAPKKK18,and ABI4 can bind the DES1 promoter,forming a regulatory loop.Taken together,these findings advance our understanding of a post-translational regulatory mechanism and suggest that ABI4 functions as an integrator of ABA and MAPK signals through a process in which DES1-produced H2S persulfidates ABI4 at Cys250.

Persulfidation-induced Structural Change of SnRK2.6 Establishes Intramolecular Interaction between Phosphorylation and Persulfidation.

Post-translational modifications (PTMs) regulate the activity of SNF1-RELATED PROTEIN KINASE2.6 (SnRK2.6), including phosphorylation and persulfidation. Here, we report how persulfidations and phosphorylations of SnRK2.6 influence each other. The persulfidation of cysteine C131/C137 altered SnRK2.6 structure, resulted in serine S175 residue more close to aspartic acid D140, who belong to ATP-γ-phosphate proton acceptor may effectively improve the transfer efficiency of phosphate groups to S175, thus persulfidation enhanced the phosphorylation level of S175. S267 and C137 were predicted to lie in close proximity on the protein surface. The phosphorylation status of S267 positively regulated the persulfidation level at C137. Tests of responses of dephosphorylated and depersulfidated mutants to ABA and the H2S-donor NaHS during stomatal closure, water loss, gas-exchange, Ca2+ influx and drought stress revealed that S175/S267-associated phosphorylation and C131/137-associated persulfidation are essential for SnRK2.6 function in vivo. Taken together, we propose a mechanistic model in which certain phosphorylations facilitate persulfidation, which changes SnRK2.6 structure and increases its activity.

Interplay between hydrogen sulfide and other signaling molecules in the regulation of guard cell signaling and abiotic/biotic stress response

Stomatal aperture controls the balance between transpirational water loss and photosynthetic carbon dioxide(CO2)uptake.Stomata are surrounded by pairs of guard cells that sense and transduce environmental or stress signals to induce diverse endogenous responses for adaptation to environmental changes.In a recent decade,hydrogen sulfide(H2S)has been recognized as a signaling molecule that regulates stomatal movement.In this review,we summarize recent progress in research on the regulatory role of H2S in stomatal movement,including the dynamic regulation of phytohormones,ion homeostasis,and cell structural components.We focus especially on the cross talk among H2S,nitric oxide(NO),and hydrogen peroxide(H2O2)in guard cells,as well as on H2S-mediated post-translational protein modification(cysteine thiol persulfidation).Finally,we summarize the mechanisms by which H2S interacts with other signaling molecules in plants under abiotic or biotic stress.Based on evidence and clues from existing research,we propose some issues that need to be addressed in the future.