Interaction between HPCA1 and melatonin signaling components modulates stomatal closure and drought tolerance in...

Melatonin is a versatile molecule that regulates plant growth and responses to multiple stresses, including drought resistance. However, the mechanism by which melatonin coordinates with other signaling pathways to regulate plant responses to stress remains largely elusive. Here, we provide evidence that melatonin induced stomatal closure and reactive oxygen species accumulation require hydrogen peroxide sensor receptor kinase HPCA1 (HYDROGEN PEROXIDE-INDUCED Ca²⁺ INCREASES1). Melatonin-induced, rather than SNP-induced, transcriptomic reprogramming was altered in hpca1 and hpca1 pmtr1 mutants, further supporting that melatonin-induced signaling depends on HPCA1. Notably, HPCA1 was found to interact with G-protein alpha subunit GPA1 and putative phytomelatonin receptor PMTR1, revealing a novel regulatory layer linking melatonin signaling, H₂O₂ signaling, and G-protein signaling. Disruption of HPCA1 and PMTR1 decreased tolerance of Arabidopsis to drought stress. Collectively, our study provides insights into the role of receptor-like kinases in orchestrating different signaling pathways, thus conferring plant responses to stress.