Identification of the MYC gene family in Camellia oleifera and the role of CoMYC2-like genes in growth and stress responses

Abstract

The myelocytomatosis (MYC) transcription factors are crucial regulators of plant growth, development, and stress responses. In this study, we identified and characterized the CoMYC gene from Camellia oleifera Abel. and investigated its functional roles through heterologous expression in Arabidopsis thaliana. Bioinformatic analysis revealed that the 31 CoMYC genes are unevenly distributed across chromosomes, with CoMYC clustered in phylogenetic Group 6 and CoMYC2-like showing high homology to CsMYC5.4 from tea plants. Conserved motif and promoter analyses indicated that CoMYC contains hormone- and stress-responsive cis-elements, suggesting its involvement in developmental and environmental adaptation processes. Subcellular localization confirmed the nuclear targeting of CoMYC2-like, with tissue-specific expression peaks in roots and stems. Overexpression of CoMYC2-like in Arabidopsis thaliana resulted in enhanced lignification, thicker stems, elongated siliques, and increased seed number, accompanied by elevated lignin content and xylem development. Under drought and salt stresses, transgenic lines exhibited reduced root growth inhibition, lower superoxide anion and MDA (malondialdehyde) accumulation, enhanced antioxidant enzyme activities (CAT (catalase), POD (peroxidase), SOD (superoxide dismutase)), the proline content was increased, the expression of antioxidant-related genes was increased, indicating improved stress tolerance. Notably, CoMYC2-like-overexpressing plants showed greater sensitivity to salt than drought, highlighting its differential regulatory roles in stress adaptation. Our findings demonstrate that CoMYC2-like modulates lignin biosynthesis and stress resilience, providing insights into MYC-mediated mechanisms in woody plants and potential targets for crop improvement.