Integrative analysis in WGBS and transcriptome profiles of an temperature sensitive etiolation tea plant cultivar 'Zhonghuang 2'
The green tea made from the etiolation shoots and leaves have fresh taste and strong aroma. 'Zhonghuang 2 (ZH2) is a natural etiolation mutant and its shoots are etiolation in spring and turn green in summer. Two conditions including the relative high temperature (LT, 26 / 22oC) and the relative low temperature (LT, 18 / 14oC) were to find out the etiolated reason of ZH2. We confirmed ZH2 was a low-temperature sensitive tea plant cultivar, and the reason of shoots etiolation at LT was the reduction of stacked grana, which could cause the lack of photoreaction. We identified 1279 differentially expressed genes (DEGs), most of them were related to cytochrome synthesis and chloroplast development and function by RNA-seq. Through the whole-genome bisulfite sequencing (WGBS) assay, we found that the dynamic of DNA methylation level in three contexts (CG, CHG and CHH) was all decreased at LT, and the change was most obvious in the CHH context. According the result of cross analysis, 56 genes were identified with significant changes in both expression and DNA methylation levels. A large number of them were related to chloroplast development and chlorophyll synthesis. This study demonstrated that the DNA methylation was involved in the low-temperature regulated etiolation process of young shoots in ZH2. Change of the DNA methylation level was associated with the gene expression level, thus affecting the structure and function of chlorophyll and chloroplast, even reduced photosynthesis, which might have a phenotypic impact on the color of shoots and leaves. And it laid the foundation for studying the etiolation process from an epigenetic perspective. Overall design: we set up two treatments of high temperature (HT) and low temperature (LT) to investigate the etiolation mechanism of young shoots of 'Zhonghuang 2' cultivar under the low temperature. And the HT is the control group and the LT is the treatment group.