Functional Study Of Apple MdVQ17 Gene In Response To Drought And Salt Stresses

VQ protein(Valine-glutamine motif containing proteins)is an important class of transcriptional regulatory cofactors.It is not only involved in regulating the growth and development of flowers,leaves,seeds,hypocotyls and other organs of plants,but also in regulating the response of plants to salt,drought,temperature and pathogens stresses.In this study,we cloned the Md VQ17 gene of apple,analyzed the expression pattern of Md VQ17 under drought and salt stresses,and identified the resistance regulation function of Md VQ17 under drought and salt stresses through the transgenic technology.The main results are as follows:1.The total length of apple Md VQ17 was 486 bp and the length of the encoded protein was 161 aa;The analysis of the cis-acting elements of the promoter showed that the promoter sequence of Md VQ17 contained various cis-acting elements which responding to stress;Subcellular localization analysis showed that Md VQ17 protein was located in nucleus and cytomembrane;The result of q RT-PCR analysis found that Md VQ17 expression was induced by drought and salt stresses.2.Yeast two-hybrid experiments showed that Md VQ17 protein could interact with the proteins of Md WRKY transcription factor family I and IIc subgroups,while didn’t interact with the other Md VQ proteins.In addition,the VQ domain and flanking sequences of Md VQ17 were required for interaction with Md WRKY transcription factors.3.Overexpression of Md VQ17 enhanced the resistance of Arabidopsis to drought and salt stresses at the seed germination stage,seedling stage and mature plant stage.Under different concentrations of mannitol and Na Cl treatments,the seed germination rate and seedling fresh weight of Md VQ17-overexpressing transgenic Arabidopsis lines were significantly higher than those of ‘Col’;Under drought and salt stresses,Md VQ17-overexpressing transgenic Arabidopsis lines increased proline content,SOD activity,POD activity,and CAT activity,while decreasing water loss rate,relative electrical conductivity,MDA content,superoxide anion and hydrogen peroxide content.Furthermore,the transcription levels of many stress-induced genes in Md VQ17-overexpressing transgenic Arabidopsis were significantly higher than those of ‘Col’.Therefore,Md VQ17-overexpressing transgenic Arabidopsis increased the drought and salt tolerance.4.Md VQ17 overexpression increased the resistance of apple Orin callus to salt and osmotic stresses.Under Na Cl and mannitol treatments,Md VQ17 transgenic apple callus had significantly higher fresh weight than the control,and showed stronger stress resistance than the control.The result of q RT-PCR analysis showed that the transcription levels of some stress-induced genes in Md VQ17 transgenic apple callus were significantly higher than those of the control.These results indicated that overexpression of Md VQ17 could promote the transcription of stress-related genes,thereby increasing the transgenic Orin apple callus tolerance to osmotic and salt stresses.