Function Analysis Of Arabidopsis Glycosyltransferase Gene UGT75X In Plant Adaptation To Stresses

As a plant hormone,abscisic acid(ABA)plays an important role in plant dormancy,stomatal closure,seed germination,embryo development,fruit ripening and abiotic stress responses.Glycosyltransferases are a class of enzymes that specifically catalyze the glycosylation of the receptor molecules,thereby altering these molecules in respect to their stability,water solubility,biological activity and subcellular localization.Glycosyltransferases play an crucial function in maintaining plant normal growth and development and regulating the metabolic balance of plant cells.Glycosyltransferase superfamily includes a huge number of members and catalyzes a wide range of substrates involved in many different physiological processes.However,little is known about their physiological roles for most members of plant glycosyltransferase family.Publicly available microarray data showed that glycosyltransferase UGT75X can be induced by abiotic stress,suggesting that this gene may be involved in plant response to stresses.In this paper,the glycosyltransferase gene UGT75X was invesitugated to explore its physiological role in the adaptability of plants to adversity.The main research contents and results are as follows.Through the qRT-PCR analysis and promoter:GUS transgenic plants,it was found that UGT75X gene could be up-regulated by ABA,salt and drought.In vitro biochemical analysis indicated that UGT75X enzyme could glycosylate abscisic acid.It was also demonstrated that the crude soluble protein from transgenic plants overexpressing UGT75X gave an increased enzyme activity toward ABA than the crude protein from wild type plants,confirming the UGT75X activity to ABA.We further studied the abiotic stress tolerance of UGT75X transgenic plants.It was observed that the germination rate and green cotyledons rate of UGT75X overexpressing lines were higher than those of wild type under salt,drought and ABA treatments,suggesting an increased stress tolerance in germination stage conferred by UGT75X overexpression.However,when post-germination seedlings were subjected to salt or drought treatments in soil,the survival rate of UGT75X overexpressing lines was lower than that of wild type,showing an stress-sensitive phenotype.In the ABA-induced stomata]closure experiment,UGT75X overexpression lines showed less sensitivity to ABA,and their stomatal opening were larger than that of wild type.It was supposed that UGT75X glycosylated ABA and reduced ABA level and signaling,thus resulting in the stress sensitive phenotypes in overexpression lines.By qRT-PCR,we analyzed the expression of ABA-dependent and independent pathway related genes in UGT75X overexpression lines and wild type.The results showed that the expression of key genes in ABA-dependent pathway such as RD22,RAB18,RD29A,RD29B,AIL1 and AREB1 was significantly lower in UGT75X overexpression lines than in wild type.Expression of DREB 2A,as a key transcription factor gene for ABA-independent pathways,was also significantly lower in UGT75X overexpression lines than in wild type after stress treatment.These results suggested that the negative contribution of UGT75X gene to resistance against stresses after germination may be due to the reduced gene expression on ABA-dependent and ABA-independent pathways.In summary,the physiologicalrole of UGT75X gene in plant adaptation to abiotic stresses was studied in this paper.The activity of glycosyltrasferase UGT75X toward ABA was found and the contrast physiological role for UGT75X to play in germination stage and post germination stage was revealed.The study will help us to understand the physiological function of glycosyltrabsferases and the molecular mechanism of plant tolerance to abiotic stresses.Also,this study may lay a theoretical foundation for crop improvement aiming at increased stress tolerance,particularly at germination stage.The work also needs further study using the UGT75X mutants to dissect the function of this glycosyltransferase.