MYC2 and MYC3 orchestrate pith lignification to defend Nicotiana attenuata stems against a stem‐boring weevil

Summary Lignin is a key structural polymer that also serves as a potent defense against biotic stress. Herbivore‐induced, jasmonate‐dependent pith lignification in Nicotiana attenuata plays a crucial role in defense against the stem‐borer Trichobaris mucorea . However, the regulatory mechanisms underlying herbivore‐induced lignification remain largely unknown. We demonstrate that NaMYC2 and NaMYC3 orchestrate pith‐specific lignification in response to T. mucorea attack. RNA‐seq analysis reveals that monolignol biosynthetic genes and polymerization‐associated genes fail to be induced in Namyc2/3 double mutants upon T. mucorea attack. Among NaMYC2/3 ‐dependent genes in the attacked pith, we identify NaTHT1 , responsible for synthesizing the noncanonical monolignol N ‐FT. Using Natht1 mutants, we further show that N ‐FT plays a key role in stem defense. Additionally, we identify NaNEC1a and NaNEC1c , NaMYC2/3 ‐dependent superoxide dismutases in the pith. Nanec1a / 1c double mutants exhibit reduced lignification and enhanced larval performance, supporting a direct link between superoxide metabolism and induced lignification. Our findings reveal a NaMYC2/3 ‐mediated regulatory network in the pith that integrates monolignol biosynthesis, lignin polymerization, and noncanonical monolignol biosynthesis, thereby enhancing stem defense against T. mucorea .