Jasmonates Promote Myrosin Idioblast Cell Development via MYC2-Mediated Activation of the FAMA-bHLH090 Pathway in Arabidopsis

Myrosin idioblast cells (MIs) are specialized cellular structures that synthesize and store myrosinase, a crucial enzyme in the glucosinolate (GSL)-myrosinase system important for the defense of cruciferous plants against herbivores and pathogens. Jasmonates (JAs) are defense-related phytohormones that increase resistance to insect feeding through promoting GSL biosynthesis, but the detailed mechanism of JAs in MI development remains to be fully explored. Here, we conducted a systematic investigation into the regulatory role of jasmonic acids (JAs) in the development of MI in Arabidopsis (Arabidopsis thaliana). Phenotypic analyses revealed that MeJA exogenous application significantly increases the number and area ratio of MIs in wild-type plants. JAs promoted MI development via the core COI1-JAZ1-MYC2 module, which depends on the key regulator FAMA. Biochemical analysis suggested that at the transcription level, MYC2 directly binds to the promoter region of FAMA, thereby activating expression. Considering protein interactions, MYC2 associates with FAMA and enhances transcription of the downstream target gene bHLH090. Genetic evidence corroborated that the functionality of MYC2 depends on FAMA. Furthermore, JAZ1 functions as a competitive inhibitor of the MYC2-FAMA interaction. Increasing the JA concentration caused FAMA upregulation and JAZ1 degradation, yielding the formation of abundant FAMA-MYC2 complexes, which promote MI development.