Comprehensive transcriptome analyses reveal differential gene expression profiles of Camellia sinensis axillary buds at para-, endo-, ecodormancy, and bud flush stages

Authors: HAO, XINYUAN - Chinese Academy Of Agricultural Sciences; YANG, YAJUN - Chinese Academy Of Agricultural Sciences; YUE, CHUAN - Chinese Academy Of Agricultural Sciences; WANG, LU - Chinese Academy Of Agricultural Sciences; Horvath, David; WANG, XINCHAO - Chinese Academy Of Agricultural Sciences

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2017
Publication Date: 4/18/2017
Citation: Hao, X., Yang, Y., Yue, C., Wang, L., Horvath, D.P., Wang, X. 2017. Comprehensive transcriptome analyses reveal differential gene expression profiles of Camellia sinensis axillary buds at para-, endo-, ecodormancy, and bud flush stages. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2017.00553.
DOI: https://doi.org/10.3389/fpls.2017.00553

Interpretive Summary: Tea plant (Camellia sinensis), is the crop from which we get tea and is one of the most important agricultural crops in China. It is also grown in select locations in the US as both a crop and an ornamental plant. Tea plant is unusual in that it is a broad leafed perennial woody evergreen shrub capable of growing in temperate regions of the world. As such, it enters dormancy just like many trees and shrubs in the fall, but does not lose its leaves. The buds of tea plants – like most temperate trees and shrubs go dormant in the fall and, after a predictable period of time in near freezing temperatures, these buds become capable of growing again once temperatures warm up enough. Very little is known about how tea plant bud growth is controlled during the various seasonal changes. We do know that light and temperature, as well as the accumulation of nutrients in the summer impact bud dormancy and growth. Understanding how bud growth is controlled by these signals is important given the impacts of global warming will have on perennial crops such as tea plant. If buds do not get their needed chilling requirement, they may not grow in the spring, and if unusual warm spells occur too early in the spring or too late in the fall, buds could start growing and then get killed by the returning cold temperatures. In this paper, we used a gene sequencing technology to look at what genes were turned on and off as the buds passed through the various seasons. We found that many of the same genes and processes that control bud growth and dormancy in the model plant poplar were similarly turned on and off in tea plants suggesting that evergreen and deciduous broad leafed plants act similarly. We also found some specific genes that might be useful for controlling bud dormancy in tea plant and other perennial crop species such as apples and blueberry.

Technical Abstract: Winter dormancy is an important biological feature for tea plant to survive cold winters, and it also affects the economic output of tea plant, one of the few woody plants in the world whose leaves are harvested and one of the few non-conifer evergreen species with characterized dormancies. To discover the bud dormancy regulation mechanism of tea plant in winter, we analyzed the global gene expression profiles of axillary buds at the paradormancy, endodormancy, ecodormancy and bud flush stages by RNA-Seq analysis. In total, 16,125 differentially expressed genes (DEGs) were identified among the different measured conditions. Gene set enrichment analysis was performed on the DEGs identified from each dormancy transition. Enriched GO terms, gene sets and transcription factors were mainly associated with epigenetic mechanisms, phytohormone signaling pathways, and callose-related cellular communication regulation. Furthermore, differentially expressed transcription factors as well as chromatin- and phytohormone-associated genes were identified. GI-, CAL-, SVP-, PHYB-, SFR6-, LHY-, ZTL-, PIF4/6-, ABI4-, EIN3-, ETR1-, CCA1-, PIN3-, CDK- and CO-related gene sets were enriched; in particular, ERF, MYB and Dof were the major transcription factors up-regulated at the endodormancy and ecodormancy stages, while MIKC-MADS and bHLH were down-regulated. Moreover, the gene sets related to HD1, DNA methyltransferases and MET1 were down-regulated when buds entered endodormancy. Histone-lysine N-methyltransferase, HTA7, and CHR32 were the top DEGs showing low expression levels at endodormancy and ecodormancy. A total of 119 auxin-associated genes were identified, and their expression profiles reflected the active or dormancy status of buds. Based on sequence homology analysis, we summarized the key genes with significant expression differences in poplar and tea plant. The major molecular pathways involved in tea plant dormancy regulation are consistent with those of poplar to a certain extent; however, the gene expression patterns varied. This study provides the global transcriptome profiles of overwintering buds at different dormancy stages and is meaningful for improving the understanding of bud dormancy in tea plant.