HB 34‐ WRKY 40 module regulates floral transition by fine‐tuning the transcription of FLOWERING LOCUS T in Arabidopsis

The transition from vegetative to reproductive growth is a pivotal developmental switch in plants, requiring tight coordination with other energy-intensive processes, such as immunity. Our recent work revealed that the homeobox transcription factor HB34 suppressed jasmonic acid biosynthesis but promoted the expression of growth-related genes to balance plant immunity and vegetative growth in Arabidopsis. Here, we find that HB34 also regulates the transition from vegetative to reproductive growth by the HB34-WRKY40-FT transcriptional cascade. In long-day conditions, HB34 promotes flowering by directly repressing the transcription factor WRKY40, whereas the heterodimer of MIF3-HB34 attenuates HB34-WRKY40 binding and de-represses the expression of WRKY40. In turn, WRKY40 functions as a transcriptional repressor of FLOWERING LOCUS T (FT) and recruits a histone H3 lysine 4 (H3K4) demethylase JMJ17 to remove H3K4me3, thereby fine-tuning FT expression and proper flowering. Together, these findings identify a HB34-WRKY40-FT regulatory module that integrates transcriptional and epigenetic mechanisms to fine-tune the floral transition, and extend the functional repertoire of HB34 from immune regulation to the control of floral transition, highlighting its role as a molecular integrator of plant development and immunity.