Arabidopsis HY5 enhances jasmonate responses by directly suppressing the expression of the JAZ1 gene in a FIN219/JAR1-dependent manner

Abstract

Light is a key environmental signal that regulates plant growth and development. ELONGATED HYPOCOTYL 5 (HY5), a bZIP transcription factor, is a central positive regulator of photomorphogenesis in Arabidopsis thaliana, integrating light and hormone signaling pathways. However, the molecular role of HY5 in jasmonate (JA) signaling remains unclear. Here, we show that methyl jasmonate (MeJA) substantially induces HY5 protein accumulation in a FIN219/JAR1-dependent manner. Genetic evidence indicates that HY5 and FIN219 act synergistically to inhibit hypocotyl growth and coordinate defense-related transcriptional networks. Loss of HY5 function results in hypersensitivity to MeJA-mediated inhibition of hypocotyl elongation, and transcriptomic analyses reveal disturbances in numerous light- and JA-responsive genes. HY5 represses JAZ1 expression by binding to its G-box-containing promoter and physically interacts with JAZ1, suggesting both transcriptional and post-translational regulation. Furthermore, HY5 and MYC2 compete for binding at the JAZ1 promoter, modulating JA responses under far-red light. Together, our findings uncover a regulatory mechanism in which HY5 fine-tunes JA signaling and seedling development by integrating light and hormone cues. This work provides new insights into HY5-mediated crosstalk and identifies potential targets to improve stress resilience in crops.