Structural and functional organization of the MYC transcriptional factors in Camellia sinensis

Genome-wide identification, expression analysis of the MYC family in Camellia sinensis, and potential functional characterization of CsMYC2.1 have laid a solid foundation for further research on CsMYC2.1 in jasmonate (JA)-mediated response. Myelocytomatosis (MYC) of basic helix-loop-helix (bHLH) plays a major role in JA-mediated plant growth and developmental processes through specifically binding to the G-box in the promoters of their target genes. In Camellia sinensis, studies on the MYC gene family are limited. Here, we identified 14 C. sinensis MYC (CsMYC) genes, and further analyzed the evolutionary relationship, gene structure, and motif pattern among them. The expression patterns of these CsMYC genes in different tissues suggested their important roles in diverse function in tea plant. Four MYC transcription factors with the highest homology to MYC2 in Arabidopsis were localized in the nucleus. Two of them, named CsMYC2.1 and CsMYC2.2, exhibited transcriptional self-activating activity, and, therefore, could significantly activate the promoter containing G-box motif, whereas CsJAM1.1 and CsJAM1.2 lack the transcriptional self-activating activity, indirectly mediating the JA pathway through interacting with CsMYC2.1 and CsMYC2.2. Furthermore, Yeast Two-Hybrid (Y2H) and Bimolecular Fluorescent Complimentary (BiFC) assays showed that CsMYC2.1 could interact with CsJAZ3/7/8 proteins. Genetically, the complementation of CsMYC2.1 in myc2 mutants conferred the ability to restore the sensitivity to JA signals. The results provide a comprehensive characterization of the 14 CsMYCs in C. sinensis, establishing a solid foundation for further research on CsMYCs in JA-mediated response.