Characterization of CsWRKY29 and CsWRKY37 transcription factors and their functional roles in cold tolerance of tea plant

The WRKY gene family is most widely known as being the key plant transcription factor family involved in various stress responses and affecting plant growth and development. In this study, a total of 86 members of the CsWRKY genes were identified from the tea plant genome. Most of these genes contain several important Cis-regulatory elements in the promoter regions associated with multiple stress-responses. These genes were further classified into three groups, I, II, and III, each with 21, 58, and 7 members, respectively. We showed evidence that tandem duplications, but not the whole genome duplication, are likely to drive the amplification of CsWRKY genes in tea plants. All the 86 CsWRKY genes showed differential expression patterns either in different tissues, or under exposure to diverse abiotic stresses such as drought, cold acclimation, and MeJA treatments. Additionally, the functional roles of two genes, CsWRKY29 and CsWRKY37, were examined under cold stress; and the silencing of these genes resulted in tea plant phenotypes susceptible to cold stress. Moreover, transgenic Arabidopsis lines overexpressing CsWRKY29 and CsWRKY37 genes showed higher survival rates and lower malondialdehyde levels under freezing treatment than the wild type plants. The core findings from this work provide valuable evolutionary pattern of WRKY gene family and underpinning the underlying regulatory roles of CsWRKY29 and CsWRKY37 from tea plants that conferred cold tolerance in transgenic Arabidopsis plants.