The HD-ZIP II Transcription Factors HAT3 and ATHB4 Fine-Tune Auxin and Cytokinin Pathways During Flower Development.

Flowers are key reproductive structures for many plant species. They are essential for seed and fruit production, and their development is tightly regulated by hormonal and genetic networks. The homeodomain transcription factors HAT3 and ATHB4 are known regulators of adaxial identity and hormone response. We demonstrate that flowers of the hat3 athb4 double mutant emerge at wider divergence angles relative to the wild type, a phenotype reflecting modified phyllotaxy and regulated by low auxin conditions. In addition, hat3 athb4 flowers exhibit aberrant trichome patterning on their sepals associated with enhanced sensitivity to cytokinin (CK). Through RNA-seq analysis of hat3 athb4 inflorescences, we identify the misregulation of genes involved in auxin biosynthesis (YUCCAs), auxin transport (PID), and CK metabolism (CKXs) and transport (PUPs). These findings suggest that HAT3 and ATHB4 fine-tune the auxin/CK balance and coordinate critical pattern events during reproductive development, offering new insight into hormone-mediated regulation of floral patterning.