The Mechanism Of Exogenous Polyamine In The Regulation Of Wheat Grain Filling Under Drought Stress

Grain filling of wheat is very important for the formation of final grain yield,while drought during grain filling stage will significantly affect the grain filling of wheat.Polyamines,as an important plant hormones,play an important regulatory role in grain filling.In this study,Xinong 979 was used and subjected to well-watered(WW)and drought stress(DS)from anthesis until maturity.Exogenous spermidine(Spd,S)and methylglyoxal-bis(guanylhydrazone)(Polyamine synthesis inhibitors,MGBG,M)was externally sprayed on wheat panicles under drought stress,deionized water was respectively applied to wheat panicles under well-watered(CK1)and drought stress(CK2).Inferior grains of wheat were analyzed by RNA sequencing,The aims of this study were reveal the molecular mechanism of the inferior grains of wheat in response to drought stress and how Spd regulate the filling of inferior grains of wheat under drought stress in the level of transcription.Additionally,external spermidine were applied to wheat panicles under drought stress and grain weight during filling process was investigated;besides,dry matter accumulation and transport,the activities of antioxidant enzymes(SOD,POD,and CAT),malondialdehyde(MDA)content,chlorophyll content and temperature in flag leaves were also measured for explaining the mechanism of such effect.This study was aimed at investigate the effect of Spd on the grain filling of wheat under drought stress and its related mechanism,and then provide some theoretical basis for alleviating the inhibitory effect of drought stress on wheat grain filling.The main results are as follows:1.After filtration,according to the screening criteria,1076 differential expressed genes were detected in CK2 VS CK1,among which 877 genes were up-regulated and 199 genes were down-regulated.GO enrichment analysis showed that the up-regulated genes were mainly enriched in response to various stress and protein folding,while down-regulated genes were mainly enriched in cell division,DNA replication,cell proliferation,mitotic nuclear division,cell cycle and epigenetics related biological process.KEGG enrichment analysis indicated that up-regulated genes were significantly enriched in protein processing in endoplasmic,endocytosis,plant-pathogen interaction,spliceosome and plant hormone signal transduction,while the down-regulated genes were significantly enriched in carotenoid biosynthesis,plant hormone signal transduction and synthesis and degradation of ketone bodies.2.Of the 496 differential expressed genes in S VS CK2,346 and 150 genes were found to be up-and down-regulated,respectively.The up-regulated genes were significantly enriched in serine-type endopeptidase inhibitor activity,peroxiredoxin activity and antioxidant activity in terms of molecular function.Logical trend analysis was performed on the differential expressed genes of S,CK2 and M,the results showed that the genes in 0 trend diagram were significantly enriched in translation,RNA methylation,ribosome biogenesis and so on in terms of biological process.KEGG enrichment analysis indicated that genes in 0 trend diagram were significantly enriched in ribosomes and oxidative phosphorylation,while genes in 7 trend diagram were significantly enriched in ribosomes ribosome biogenesis in eukaryotes,RNA transport and spliceosome.3.Drought stress significantly inhibited grain filling of wheat,exogenous Spd significantly promoted the grain filling under drought stress and significantly increased the grain filling rate and grain weight of wheat under drought stress.Drought stress increased the amount and rate of mobilization of pre-anthesis stored assimilates in vegetative organ and contribution to grain weight,but reduced the contribution of post-anthesis assimilates to grain weight,exogenous Spd significantly promoted the amount of post-anthesis assimilates transferring into grain and the contribution of post-anthesis assimilates to grain weight under drought stress.4.Drought stress significantly decreased the activities of antioxidant enzymes(SOD,POD,CAT)and chlorophyll,and increased MDA content and leaf temperature in flag leaf in middle and later periods of the grain filling.Exogenous Spd increased activities of antioxidant enzymes and chlorophyll content and decreased MDA content and temperature in flag leaves during filling process under drought stress.