Whole-Genome Identification and Expression Profiles of WRKY Genes Related to the Leaf Expansion Period in the Camphor tree

The camphor tree (Cinnamomum camphora) is of great economic and ecological value, and the WRKY transcription factor (TF) family plays a crucial role in regulating plant growth and development as well as the responses toward environmental changes. However, the research on WRKY TFs in C. camphora remains scarce, and their roles in the leaf expansion period are unknown. In this study, we identified WRKY TFs across the C. camphora genome, followed by a phylogenetic analysis. Then, we conducted RNA sequencing and qPCR experiments on leaves collected from three distinct stages during leaf expansion (S1, S2, and S3) to determine which WRKY genes showed significant up-regulation during these stages. Here, a total of 72 CcWRKY TFs were found in the C. camphora genome, and they were phylogenetically clustered with corresponding subfamilies of Arabidopsis thaliana. These CcWRKY proteins were divided into three major groups (I, II, and III), where group II consisted of five subgroups. We found that three genes (CcWRKY24, CcWRKY42, and CcWRKY70) were upregulated from both S1 to S2 and from S1 to S3. The expression level of CcWRKY24 increased gradually from S1 to S3, while CcWRKY42 and CcWRKY70 exhibited higher expression levels in S2 and S3 than in S1. These predicted gene expression profiles were further confirmed by qPCR experiments. In summary, this study analyzed WRKY TFs in C. camphora from a genome-wide perspective and paves the way for future research on the functions of CcWRKYs.