The Arabidopsis Glycosyltransferase Gene UGT73C7 Activates Resistance-like Gene SNC1 Mediated Immune Responses

Pathogenic bacteria exist everywhere in nature.Pathogenic bacteria proliferate in intercellular spaces(apoplast)after entering through multiple pathway.Pathogenic bacteria can lead to plant disease seriously.Plant immune system have evolved sophisticated defense mechanisms along with the evolution of the plant pathogenic bacteria.Plant immune system include innate immune system and systemic acquired resistance(SAR).Innate immune system responds to infection throughPAMP-Triggered Immunity(PTI)and Effector-Triggered Immunity(ETI).ETI islargely mediated by resistance(R)proteins encoded by R-genes that directly or indirectly perceive the pathogen effectors.The R-gene SNC1 has been reported in many papers but its activation mechanism is obscure.Family-1 UDP glycosyltransferases(UGTs)are enzymes responsible for glycosylation of plant small molecular compounds,which catalyze the transfer of ’,sugar moieties from activated donor molecules to specific acceptor molecules,thus change their biological activity,water-solubility,transport characteristics and binding properties with receptors.Therefore,glycosyltransferases play significant roles in maintaining cell homeostasis,regulating plant growth and development.Researches on plant glycosyltransferases,especially the family 1 glycosyltransferases of Arabidopsis thaliana in recent years,have demonstrated the wide range of biological functions of plant glycosyltransferases.Recent studies have shown that plant glycosyltransferases were involved in the regulation of plant responses to biotic stresses,but their specific mechanisms of action remain to be determined.Until now,there is no report on the involvement of UDP-glycosyltransferases in ETI.Based on the gene chip data and recent studies,it was speculated that Arabidopsis glycosyltransferase gene UGT73C7 mediates plant innate immune response.In this thesis,we studied the function of UGT73C7 through its mutants and overexpression strains.Some experimental results have been acquired.1.Arabidopsis glycosyltransferase gene UGT73C7 can constitutively activate temperature-dependent plant defense responses.Through Real-time PCR and GUS staining analyze,it was found that Arabidopsis glycosyltransferase gene UGT73C7 was significantly induced by plant pathogenic bacteria.At 22℃,UGT73C7 overexpression lines(UGT73C70E)showed greatly reduced plant size and twisted leaves.The overexpression of UGT73C7 aslo resulted in enhanced resistance to plant pathogenic bacteria along with the substantial accumulation of SA and ROS and the up-regulated expression of immune-related genes.However,the phenotype of UGT73C70E and the expression level of immune-related genes except SNC1 were restored at 28 ℃.Protein encoded by UGT73C7 was found to be located in nucleus and cytoplasmic both at 22℃ and 28 ℃,suggesting a temperature-independent subcellular localization.2.The resistance-like gene SNC1 is needed for UGT73C7 activated immune responsesThe function of UGT73C7 in immune response was studied by molecular and cellular techniques.It was found that UGT73C70E constitutively up-regulated the expression of SNC1 and activated plant defense responses.We generated a UGT73C70E(-SNC1)hybrid strain by crossing UGT73C70E and Arabidopsis ecotype Ws(without SNC1 gene)and then analyzed the phenotype of this hybrid strain.It was found that the lack of SNC1 cannot activate plant defense response under the background of UGT73C7 overexpression.The phenotype of hybrid strain,the expression level of immune-related genes and the accumulation of SA and ROS were all restored,indicating that the UGT73C7 activated immune responses is mediated by SNC1.3.The signal transduction components downstream of SNC1 were essential for UGT73C7 activated immune responsesThe hybrid strains of UGT73C70E and pad4-1,UGT73C70E and eds1-1,UGT73C7OE and NaHGOE(overexpressing salicylate hydroxylasw)were generated analyzed.Our results showed that these hybrid strains restored the plant phenotypes,the expression of immmune-related genes,and the accumulation of SA and ROS.Thus UGT73C7activated immune responses rely on PAD4,EDS1 and the accumulation of SA.In conclusion,the data present in this thesis suggest that Arabidopsis glycosyltransferase gene UGT73C7 can activate the the expression of SNC1,and further activate plant immune response through the signal pathway including PAD4,EDS1 and SA.But the mechanism by which the UGT73C7 activates the expression of SNC1 needs to be further studied.