A homeobox transcription factor HB34 suppresses jasmonic acid biosynthesis but promotes the expression of growth-related genes to balance plant immunity and growth in Arabidopsis.

Activation of plant immunity is commonly associated with the biosynthesis of defense-related metabolites, such as jasmonic acid (JA) and salicylic acid (SA). However, constitutive activation of the immune response or excessive accumulation of defense metabolites often negatively impacts plant growth. The regulatory mechanisms underlying the trade-off between plant immunity and growth remain elusive. In this study, we identified a homeobox transcription factor, HB34, as a key regulator that balances plant immunity and growth by differentially regulating the expression of JA biosynthetic and growth-related genes in Arabidopsis. Loss of HB34 enhances plant resistance to the necrotrophic pathogen Botrytis cinerea but impairs plant growth and development, accompanied by constitutive activation of JA-responsive genes. Mechanistically, HB34 negatively regulates the transcription of JA biosynthetic genes to suppress JA accumulation, and blocking JA biosynthesis attenuates the enhanced Botrytis cinerea resistance of hb34. Conversely, HB34 enhances the transcription of growth-related genes, whereas overexpression of these genes partially rescues growth defects, thereby decoupling the trade-off between enhanced defense and impaired plant growth. Our findings reveal a novel mechanism whereby a single transcription factor fine-tunes the trade-off between plant growth and immunity by differentially regulating JA biosynthetic and growth-related genes in Arabidopsis.