Phosphorylation-Coupled Proteolysis of the Transcription Factor MYC2 Is Important for Jasmonate-Signaled Plant Immunity

As a master regulator of jasmonic acid (JA)–signaled plant immune responses, the basic helix-loop-helix (bHLH) Leu zipper transcription factor MYC2 differentially regulates different subsets of JA–responsive genes through distinct mechanisms. However, how MYC2 itself is regulated at the protein level remains unknown. Here, we show that proteolysis of MYC2 plays a positive role in regulating the transcription of its target genes. We discovered a 12-amino-acid element in the transcription activation domain (TAD) of MYC2 that is required for both the proteolysis and the transcriptional activity of MYC2. Interestingly, MYC2 phosphorylation at residue Thr328, which facilitates its turnover, is also required for the MYC2 function to regulate gene transcription. Together, these results reveal that phosphorylation-coupled turnover of MYC2 stimulates its transcription activity. Our results exemplify that, as with animals, plants employ an “activation by destruction” mechanism to fine-tune their transcriptome to adapt to their ever-changing environment.

作为茉莉酸（jasmonic acid, JA）信号通路介导的植物免疫应答的核心调控因子，碱性螺旋-环-螺旋（basic helix-loop-helix, bHLH）亮氨酸拉链转录因子MYC2可通过不同机制差异化调控JA响应基因的不同子集。然而，MYC2自身在蛋白质层面的调控机制仍未明确。本研究发现，MYC2的蛋白质降解对其靶基因的转录调控发挥正向作用。我们在MYC2的转录激活结构域（transcription activation domain, TAD）中鉴定出一段由12个氨基酸组成的基序，该基序同时是MYC2发生蛋白质降解及具备转录活性所必需的。值得注意的是，位于苏氨酸328位点的MYC2磷酸化修饰可促进其蛋白周转，同时也是MYC2调控基因转录功能所不可或缺的。综上，上述结果揭示了磷酸化偶联的MYC2蛋白周转可增强其转录活性。本研究证实，与动物系统类似，植物同样采用“破坏式激活”机制来精细调控转录组，以适应不断变化的外界环境。