Receptor-Like Kinase ZmRLK9 Functions as an Upstream ABA Signaling Factor Conferring Drought Resilience in Maize

The phytohormone abscisic acid (ABA) plays a pivotal role in plant drought responses. Although a substantial amount of research has concentrated on intracellular ABA receptors and SnRK2 protein kinases as the central signaling components, how the extracellular ABA signal is transduced to this core pathway remains largely unknown. Here, through a genome-wide association study mapping drought resistance in maize at the flowering stage, we identify a 4,052-bp hAT transposon insertion upstream of a leucine-rich repeat receptor-like kinase gene, named ZmRLK9, that suppresses gene expression and compromises drought resilience. ZmRLK9 functions as a plasma membrane-localized receptor kinase that transduces the extracellular ABA signal to the core ABA pathway. Upon ABA treatment, ZmRLK9 phosphorylates and promotes the degradation of an F-box protein, ZmFBP1, thereby stabilizing the core ABA signaling kinases ZmSnRK2.9 and ZmSnRK2.10. Enhancing ZmRLK9 expression or knocking out ZmFBP1 significantly enhances drought resistance in maize at both seedling and flowering stages and increases grain yield under drought conditions in the field. Collectively, our findings reveal a previously unrecognized regulatory module that operates upstream of the core ABA signaling pathway and highlight ZmRLK9 and ZmFBP1 as promising genetic targets for breeding crops with enhanced drought resilience.