Jasmonate-Responsive MYB55 Regulates Herbivore Resistance Through the Phenylpropanoid Metabolism in Rice

The jasmonate (JA) phytohormone signaling pathway is a key regulator of plant resistance to insect herbivores by mediating the biosynthesis of anti-herbivore metabolites and proteins. However, the JA-mediated regulatory network and its downstream defensive compounds in the monocot crop rice remain largely unknown. Here, we investigate the role of the MYB transcription factor MYB55 in JA-mediated rice defense against insect herbivores. Knockout of MYB55 enhances feeding by both brown planthopper (BPH) and leaf folder (LF), while having no effect on BPH oviposition. MYB55 directly binds to AC motifs in the promoters of initial phenylpropanoid pathway genes, including phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, and 4-coumaroyl:CoA ligase, as well as downstream lignin biosynthetic genes, and activates their transcription. In addition to lignin, accumulation of BPH- and LF-induced phenolic acid-amine conjugates (phenolamides) is significantly reduced in myb55 mutants compared with wild-type plants. The expression of MYB55 is induced by herbivory and regulated by JA signaling. Mechanistically, the core JA regulator MYC2 directly binds to the MYB55 promoter, forming a MYC2-MYB55 transcriptional cascade. Collectively, this study reveals that JA-responsive MYB55 enhances rice defense against BPH and LF by reprogramming phenylpropanoid metabolism toward lignin and phenolamide biosynthesis.