Jasmonic Acid Regulates Senescence By Inducing H₂O₂ Accumulation In Arabidopsis

Plant senescence is a process that leads to the decline and eventual death of cells,organs or the whole plant,which plays an important role in the whole life cycle of plants.Senescence of leaves is an important indicator of plant senescence.In the process of leaf senescence,nutrients and energy from senescence parts are recycled to the developing tissues and storage organs,so that nutrients and energy from senescence parts can be fully utilized,which has great significance in plant developmental biology.Previous studies have shown that Jasmonic acid(JA)is an important signal molecule in the process of promoting leaf senescence,while H₂O₂ also plays an important role in the process of promoting leaf senescence.However,it is not clear whether they have a coordinating role in the process of promoting leaf senescence.Our results showed that in the process of leaf senescence,MYC2(helix-loop-helix transcription factor),the core transcription factor of JA signaling pathway,directly binds CAT2(catalase 2)promoter and inhibits its expression,thus promoting the accumulation of H₂O₂ and leading to leaf senescence.The main experimental results obtained in this paper are as follows:1.Jasmonic acid promotes H₂O₂ accumulation during leaf senescenceIn this paper,treatment of methyl jasmonic acid(Me JA)results in precocious senescence phenotype of the wild-type leaves with decreased chlorophyll content,enhanced expression of senescence-associated genes SAG12(SENESCENCE-ASSOCIATE GENE12),SAG13,SAG29 and SAG113,and repressed expression of photosynthetic genes CAB1(CHLOROPHYLL A/B BINDING PROTEIN1)and RBCS(RIBULOSE BISPHOSPHATE CARBOXYLASESMALL CHAIN).Treatment with potassium iodide(KI)or glutathione(GSH),two widely-used H₂O₂ scavengers,significantly repressed JA-induced H₂O₂ accumulation and leaf senescence for increased chlorophyll content and repressed expression of SAGs.2.JA–dependent MYC2 induced H₂O₂ accumulatio in senescence leavesWe assayed H₂O₂ accumulation in the wild-type and myc2 mutant leaves treated with Me JA,and found that myc2 mutant showed a delayed senescence phenotype and lower H₂O₂ accumulation in the presence of Me JA compared with the wild type.We also found that when H₂O₂ was exogenously applied to myc2 mutant,the decreased H₂O₂ accumulation and delayed senescence of the mutant leaves were significantly reverted,this indicates that MYC2 is needed when JA induces H₂O₂ accumulation.3.MYC2 binds to the promoter of CAT2 and inhibits its expression during the senescence processOur q RT-PCR results showed that Me JA treatment markedly repressed CAT2expression,CAT2 protein accumulation and catalase activity in the wild-type leaves,but not in myc2 mutant.These result means that JA inhibits CAT2 expression through MYC2 during the senescence process.Promoter analyses showed that there are three MYC2 binding G-box motifs(CACATG)in the promoter region of CAT2,including G1,G2 and G3.35S::MYC2-GFP transgenic plants and anti-GFP antibody were used to perform chromatin immunoprecipitation Ch IP-q PCR,and we found that CAT2-G1,in the CAT2 promoter,was significantly enriched by anti-GFP antibody.We also use electrophoretic mobility shift assay(EMSA)experiment confirming that MYC2 binds to CAT2 promoter.In summary,our results suggest that JA promotes the accumulation of H₂O₂ in leaves through MYC2-mediated repression of CAT2 expression to promoting the senescence of arbidopsis leaves.