CsbZIP1-CsMYB12 mediates the production of bitter-tasting flavonols in tea plants (Camellia sinensis) through a coordinated activator–repressor network

Under high light conditions or UV radiation,tea plant leaves produce more flavonols,which contribute to the bitter taste of tea;however,neither the flavonol biosynthesis pathways nor the regulation of their production are well understood.Intriguingly,tea leaf flavonols are enhanced by UV-B but reduced by shading treatment.CsFLS,CsUGT78A14,CsMYB12,and CsbZIP1 were upregulated by UV-B radiation and downregulated by shading.CsMYB12 and CsbZIP1 bound to the promoters of CsFLS and CsUGT78A14,respectively,and activated their expression individually.CsbZIP1 positively regulated CsMYB12 and interacted with CsMYB12,which specifically activated flavonol biosynthesis.Meanwhile,CsPIF3 and two MYB repressor genes,CsMYB4 and CsMYB7,displayed expression patterns opposite to that of CsMYB12.CsMYB4 and CsMYB7 bound to CsFLS and CsUGT78A14 and repressed their CsMYB12-activated expression.While CsbZIP1 and CsMYB12 regulated neither CsMYB4 nor CsMYB7,CsMYB12 interacted with CsbZIP1,CsMYB4,and CsMYB7,but CsbZIP1 did not physically interact with CsMYB4 or CsMYB7.Finally,CsPIF3 bound to and activated CsMYB7 under shading to repress flavonol biosynthesis.These combined results suggest that UV activation and shading repression of flavonol biosynthesis in tea leaves are coordinated through a complex network involving CsbZIP1 and CsPIF3 as positive MYB activators and negative MYB repressors,respectively.The study thus provides insight into the regulatory mechanism underlying the production of bitter-tasting flavonols in tea plants.

CsTCPs regulate shoot tip development and catechin biosynthesis in tea plant (Camellia sinensis)

The growth of leaves and biosynthesis of characteristic secondary metabolites are critically important for tea production and quality control.However,little is known about the coordinated regulation of leaf development and catechin biosynthesis in tea plants.Here,we reported that TCP TFs are involved in both catechin biosynthesis and leaf development.An integrated analysis of catechin profiling and CsTCP expression in different tissues of plants under various environmental conditions at different developmental stages indicated significant correlations between the transcript levels of CIN-type TCPs and catechin production.CIN-type CsTCP3 and CsTCP4 and PCF-type CsTCP14 interacted with the MYB-bHLH-WD40 repeat(MBW)complex by forming a CsTCP3-CsTT8 heterodimer and modulating the transactivation activity of the promoters of anthocyanin synthase(CsANSl)and anthocyanidin reductase(CsANRl).Four types of microRNA/target modules,miR319b/CsTCP3-4,miR164b/CsCUC,miR396/CsGRF-GIF,and miR165b/HD-ZIPIII ones,were also identified and characterized for their functions in the regulation of the development of teaplant shoot tips and leaf shape.The results of these modules were reflected by their different expression patterns in developing buds and leaves that had distinctly different morphologies in three different teaplant varieties.Their roles in the regulation of catechin biosynthesis were also further verified by manipulation of microRNA319b(miR319b),which targets the transcripts of CsTCP3 and CsTCP4.Thus,CsTCPs represent at least one of these important groups of TFs that can integrate tea plant leaf development together with secondary metabolite biosynthesis.Our study provides new insight into shoot tip development and catechin production in tea plants and lays a foundation for further mechanistic understanding of the regulation of tea plant leaf development and secondary metabolism.