Function Analysis Of Methonal-Jasmonates Metabolic Cascade In Regulating Rice Leaf Senescence With MGWAS

Aging is a ubiquitous phenomenon in the biological world,and the aging process is a popular research topic.Leaf senescence is an important developmental stage,accompanied with the reassembling of nitrogen and other beneficial elements from senesced leaves to source tissues like young leaves and sink tissues such as seeds,which is vital for seed germination,crop yield and quality.At the meanwhile,leaf senescence is also an essential way for plants' adaption to their environments.It is difficult to clone genes controlling leaf senescence in rice via the genome-wide association study(GWAS),since leaf senescence begins after pollination and the dramatic variation in heading date of rice germplasms.Considering the well documented role of jasmonates in regulating leaf senescence,metabolic GWAS(mGWAS)based on jasmonates content might be helpful to identify key regulators of leaf senescence.A collection of 221 accessions of rice germplasms was used in this study for the determination of 10 jasmonates.Several active forms of jasmonates were found to be accumulated at significantly higher level in indica cultivars than that in japonica cultivars.Further GWAS led to the identification of 13 loci may underlying the natural variation in jasmonates content.Deepen analysis of the two most significant loci led to the speculation that OsPME1 encoding a pectin methyltesterase and OsTSD2 encoding a pectin methyltransferase may regulate jasmonates content.Subsequent determination of jasmonates in mutants and transgenic lines helped to characterize the role of OsPME1 and OsTSD2 in inducing jasmonates accumulation.Further expression analysis with 30 rice cultivars revealed that the expression of OsPME1 in indica cultivars is markedly higher than that in japonica cultivars,indicating that variation in OsPME1 expression may result in the altered jasmonates content.Delayed leaf senescence of tsd2 mutants was identified in further investigation on phenotype.The transgenic plants of OsPME1 also displayed alter dark-induced leaf senescence.Furthermore,exogenous Me-JA rescued the retarded leaf senescence in tsd2 mutants,which suggesting that delayed leaf senescence in tsd2 at least partially result from declined accumulation of jasmonates.However,the biochemical and metabolic roles of OsPME1 and OsTSD2 are irrelevant to jasmonates biosynthesis.The direct function of OsPME1 and OsTSD2 is the methylation and demethylation of cell wall pectin,which is the major source of methanol in plant.Hence,we speculated that OsPME1 and OsTSD2 regulate jasmonates synthesis by controlling the production of methanol from demethylation of cell wall pectin.Firstly,we found that OsPME11,another member of PME family,and OsPMEI-1 from PME inhibitor family effect the expression of jasmonates synthesis related genes,suggesting that genes regulating the level of pectin methylation may also effect the content of jasmonates.Further application of methanol to plant under hydroponics resulted in dramatic responses of jasmonates synthesis related genes' expression.At the meanwhile,induced accumulation of jasmonates under methanol treatment was also detected.To sum up,we identified the role of methanol-jasmonates metabolic cascade in inducing leaf senscence in rice.