Functional Study Of Apple MdVQ37 Gene In Response To Infection Of Pathogen Valsa Mali

Apple（Malus domestica Borkh.）is very popular because of its high quality and low price.China has a wide range of apple cultivation,and its output and sales rank first in the world.However,Apple Valsa Canker seriously affects the yield and quality of apple,which greatly hinders the steady development of apple cultivation industry.VQ protein（Valine-glutamine motif containing protein）is a class of plant transcriptional regulatory cofactors,which is involved in the regulating plant growth,development and defense responses.The transcriptional level of VQ genes is induced or inhibited by SA and JA,two important signaling molecules that mediate plant disease resistance response,and responds to pathogen,suggesting that VQ genes may play an important role in response to plant disease resistance.In this study,the expression patterns of apple MdVQ genes under SA,JA treatments were analyzed,MdVQ37 over-expressing transgenic apple plants obtained in the previous period were used as research materials,through physiological and biochemical analysis,RNA-Seq and qRT-PCR analysis preliminarily reveal the biological function of MdVQ37 in reducing the resistance of apple plants to apple Valsa Canker.The main findings are as follows:1.qRT-PCR results indicated that 14 MdVQs genes were affected by SA and JA,of which 9 MdVQs genes were up-regulated and 5 MdVQs genes were down-regulated under SA and JA treatments;MdVQ19 and MdVQ37 only responded to SA;MdVQ5,MdVQ12,MdVQ16,MdVQ35,MdVQ47 only respond to JA.2.qRT-PCR results revealed that MdVQ37 expression was induced by Valsa mali.Overexpression of MdVQ37 conferred transgenic apple plants susceptible to apple valsa canker,which was realated to decrease H₂O₂ content,the activities of SOD,CAT,POD,PPO,chitinase andβ-1,3-glucanase and leaf tissue compactness and thickness.3.RNA-Seq analysis showed that MdVQ37 over-expressing transgenic apple plants up-regulated 542 differentially expressed genes and down-regulated 837 differentially expressed genes compared with WT.The GO and KEGG pathway analyses indicated that the transcription factor activity and plant hormone signaling pathways were differentially influenced and enriched in transgenic lines.The content analysis of SA and SA metabolite2,5-DHBA revealed that of overexpression of MdVQ37 increased 2,5-DHBA content by regulating the expression of SA catabolism genes Md S5H1 and Md S5H2,which ultimately resulted to decrease in endogenous SA content and the disruption of the SA-dependent signaling pathway.