Transciptional Regulation Of Citrus Valencene Synthesis By CitAP2.10 And CitMYC3

Aroma is a vital trait of fruit quality and commercial value,including citrus fruits.The researches on citrus aroma mainly focused on the contrastive analysis of organic volatile compounds and the identification of structural genes,while it is limited about transcriptional regulation of citrus aroma.The present study explored the transcriptional regulation of valencene,which is the characteristic volatile of sweet orange.Citrus sinensis L.Osbeck cv.Newhall was used as the materials and the transcription factors of CitAP2/ERF and CitMYC(belonging to bHLH)were screened with their effects on CsTPS1(the valencene synthase)promoter.The mechanisms and the roles of some important regulators were analyzed and verified.The main results are as follows:1.CitAP2.10 was characterized as a regulator of valencene synthesis.During’Newhall’ fruit development,there was an obvious positive linear correlation between the gene expression patterns of CitAP2.10 and CsTPS1,which were also positively associated with the valencene content of citrus fruit.Furthermore,ethylene enhanced the expression of CitAP2.10 and the ethylene antagonist 1-MCP had the opposite effect,in parallel with the CsTPSl expression and valencene content.The study confirmed the biological effect of CitAP2.10 on inducing the transcriptional level of CsTPSl and accelerating the synthsis of valencene.2.Cit MYC3 was characterized to have the transactivation effect on CsTPSl promoter.During fruit development,the gene expression of CitMYC3 increased earlier than the CsTPS1 expression and valencene accumulation.Moreover,CitMYC3 was activated by ethylene and the response to ethylene was also ahead of the changes of CsTPSl and valencene.CitMYC3 could up-regulate the transcript abundance of CsTPS1.Meanwhile,CitMYC3 had self-activation and trans-activation on the promoter of CitAP2.10.Thus,CitAP2.10 and CitMYC3 participated in the transcriptional regulation of CsTPS1 and the regulation of citrus valencene synthesis cooperatively.3.AtWRI1,the homolog of CitAP2.10 in Arabidopsis,was found to activate the CsTPSl promoter in vivo.Meanwhile,CitAP2.10 and CitMYC3 could both activate the promoter of AtPS11,which was identified to synthesize more than 15 sesquiterpenes in Arabidopsis flowers.All the results suggest broader functions of CitAP2.10 and CitMYC3 in the regulation of sesquiterpene synthesis and the functions might be conserved in various plant species.