Functional Analysis Of Transcription Factor CsMYB8 From Citrus

With the development of citrus industry and the improvement of people's lives,fruit quality is gradually concerned.Sugar,as one of important type of primary metabolites in plant,plays key role in fruit quality.MYB transcription factors represent one of the largest gene families in plant genomes,their functions in the secondary metabolism,environmental stress and morphogenesis of organs are all well known now.However few studies about the carbohydrate metabolism regulated by MYB transcription factors have been reported.This study selected CsMYB8 as the candidate gene,which showed high identity to sucrose-responsive element binding protein family members.Explored the function of CsMYB8 based on CsMYB8-overexpressing tomato lines.The main results were as follows:1.Phylogenetic analysis of CsMYB8 indicated that CsMYB8 exhibited a close relationship with MdMYB6 and VvREBP.Southern blot analysis showed that two copies of CsMYB8 were detected in sweet oranges.Gene expression analysis showed CsMYB8 was significantly reduced during early stages of development of ‘Honganliu' sweet orange.The expression of CsMYB8 could be inhibited under UV and increased under low temperature,high temperature or ethylene treatment.2.Subcellular localization of CsMYB8 showed that CsMYB8 located in nucleus by Arabidopsis protoplast and onion epidermal cells,respectively.Transcription activation analysis showed that the CsMYB8 protein had transcriptional activation activity.3.The expression of recombinant CsMYB8 in E.coil BL21 and the purification for the recombinant protein of CsMYB8.4.Cultivation and observation of CsMYB8-overexpressing tomato lines showed that transgenic plants were exhibited increased density of trichomes.The structure of trichomes under scanning electron microscopy.Transgenic fruits showed no significant difference in the color,shape and maturity.There were no significant differences on Vc content and etgylene released amount.5.Primary metabolites analysis of CsMYB8-overexpressing tomato lines showed that the content of sucrose,glucose,fructose and lactose were significantly reduced,the content of starch was significantly increased.The expression of key structural genes of the glucose-metabolic pathway showed Rpi gene been significantly decreased in transgenic lines.6.Secondary metabolites analysis of CsMYB8-overexpressing tomato showed that there were several compounds showing significantly reduced such as caffeic acid,caffeine butyldiamine and 3-caffeoylquinic acid.The content of naringenin chalcone was significantly increased.7.AAT gene,as one of important enzyme gene of ester biosynthesis in plant,was significantly reduced in transgenic lines.However,There were no significant differences on the content of volatile compounds amount between transgenic and wild type of tomatoes.