Identification Of SDG Gene Family Members And Functional Analysis Of CsSDG36 And CsSDG43 Genes In Camellia Sinensis

The SDG(SET domain group)family is a protein family with histone methyltransferase activity in plants,which regulates the methylations of lysine on histones.SDG-mediated histone methylation regulates a number of biological processes,such as flower organ development,seed germination,root development,and stress response.Drought and low nitrogen stresses are the important abiotic stresses during the growth process,while aluminum accumulation and tolerance are key biological traits of tea plants.However,the function of histone methylation in these processes is rarely studied.In this study,CsSDGs were identified using tea genome database,phylogenetic tree analysis,domain analysis and gene structure analysis,and the function of CsSDGs was speculated by tissue-specific and abiotic stress-induced expression analyses.Based on protein,gene expression and physiological analyses of tea plants,CsSDG36 and CsSDG43 overexpression lines were used to verify their functions under drought,high aluminum and low nitrogen stresses.The main results are as follows:(1)A total of 46 CsSDGs were identified by genome-wide search with the conserved domain.By phylogenetic tree,domain and gene structure analyses,46 CsSDGs were classified into 5 types,including E(Z),ASH1,TRX,SU(VAR)and VI/VII.In addition,tissue-specific and abiotic stress-induced expression analysis showed that 46 CsSDGs had different expression patterns in different tissues and in response to various abiotic stresses.(2)Drought stress induced the down-regulation of histone H3K4 methylation and up-regulation of histone H3K4 acetylation in tea leaves,revealing the potential negative regulation of histone H3K4 methylation in drought tolerance.Phenotypic identification of the CsSDG43 overexpression Arabidopsis seedlings showed that overexpression of CsSDG43 promoted water loss,increased ROS pressure,inhibited expression of drought tolerance genes such as AHG3,and decreased plant hyperosmotic tolerance.Phenotypic identification of the CsSDG36 overexpression Arabidopsis seedlings showed that overexpression of CsSDG36 increased stomatal density,promoted water loss,increased ROS pressure,and decreased hyperosmotic tolerance of Arabidopsis thaliana.RNA-Seq and qRT-PCR analyses revealed that CsSDG36 regulate chromatin assembly,microtubules assembly and leaf stomatal development pathways.(3)The inhibitors of histone H3K4 demethylation reduced the aluminum tolerance of tea plants,revealing the potential negative regulation of histone H3K4 methylation in aluminum tolerance.Phenotypic identification of the CsSDG36 and CsSDG43 overexpression Arabidopsis seedlings showed that overexpression of CsSDG43 and CsSDG36 resulted in inhibited organic acid secretion,inhibited initiation of lateral root development,and reduced plant tolerance to high aluminum.(4)Low nitrogen induced the expression of CsSDG36 and CsSDG43 gene in Echa 10(Camellia sinensis(L.)O.Kuntze cv.Echa 10),Longjing 43(Camellia sinensis(L.)O.Kuntze cv.Longjing 43)and Echa 1(Camellia sinensis(L.)O.Kuntze cv.Echa 1)tea varieties,revealing the potential positive regulation of histone H3K4 methylation in Nitrogen Use Efficiency.Phenotypic identification of CsSDG36 and CsSDG43 overexpression Arabidopsis seedlings showed that overexpression of CsSDG36 and CsSDG43 activated the expression of NRT2 family genes and enhanced the nitrogen uptake of plants under low nitrogen stress.