Transcription factor CsMYB192 regulates cellulose biosynthesis and secondary cell wall formation in Camellia sinensis

Tenderness of tea leaves tightly associates with the quality and commercial value of tea beverage. Cellulose synthesis and secondary cell wall (SCW) formation negatively correlate with the tenderness of tea shoots. Light is one of the core environmental factors affecting cellulose synthesis and SCW formation; however, how light quality regulating cellulose accumulation remains unclear in tea [Camellia sinensis (L.) Kuntze]. In this study, we identified a transcription factor CsMYB192, which was repressed by red/blue light at both transcription and protein levels, could promote cellulose biosynthesis and SCW formation by targeting cellulose synthase-encoding genes CsCesAs in tea plants. Specifically, treatment with red/blue light individually or simultaneously significantly reduced cellulose contents, thickness of SCW, as well as transcription of CsCesAs to a certain extent in new shoots. Further analysis showed that CsCesA4, 7, 8A, and 8B, four CsCesAs involved in SCW cellulose biosynthesis, interacted with each other and contributed to cellulose accumulation and SCW formation in tea leaves. Moreover, by performing yeast one-hybrid screening of the tea cDNA library using promoter of the four CsCesAs as baits, respectively, we identified a common R2R3-MYB transcription factor CsMYB192 shared by the four targets. Further analysis revealed that CsMYB192 directly bound to promoter of the four targets and activated their transcriptions. Moreover, silencing CsMYB192 using the tobacco rattle virus (TRV)-mediated gene silencing system resulted in compromised cellulose biosynthesis and SCW formation in tea plants, while ectopic expression of CsMYB192 in Arabidopsis mutant myb46, which is a homolog of CsMYB192, rescued the growth defect, as well as decreased cellulose contents, of the mutant plants. Therefore, our data dissect a possible pathway by which red/blue light regulates cellulose biosynthesis and SCW formation through the CsMYB192-CsCesAs module in tea plants, which might be involved in manipulating the tenderness of tea shoots.