Leucine-Rich Repeat Receptor-Like Kinase FON1 Regulates Drought Stress and Seed Germination by Activating the Expression of ABA-Responsive Genes in Rice

Receptor-like kinases (RLKs) play important roles in regulating plant development and responses to various environmental stresses. FLORAL ORGAN NUMBER1 (FON1), a leucine-rich repeat receptor-like kinase, was reported to participate in the control of vegetative and reproductive development, but little is known about its function in response to abiotic stress in rice. Here, we reported that FON1 was involved in the regulation of water stress and seed germination process by mediating the expression of abscise acid (ABA)-responsive genes. FON1 was expressed mainly in root and shoot and could be induced by NaCl, drought, and ABA treatment. Transgenic plants overexpressing FON1 exhibited enhanced drought stress and reduced accumulation of H₂O₂ and malondialdehyde compared to the control. In contrast, RNAi-mediated disruption of FON1 resulted in decreased drought stress associated with the excessive ROS accumulation. At the transcription level, several stress-related and ABA-responsive genes, including LEA3, OsbZIP46, APX3, APX5, and CATB, were upregulated in transgenic plants overexpressing FON1, but correspondingly downregulated in RNAi plants. Moreover, overexpression of FON1 led to delayed seed germination, inhibited early root growth, and increased susceptibility to ABA, likely by activating the expression of ABA-responsive homeodomain transcription factors. These results provide new insight into the function of FON1 in the regulation of drought stress and early growth processes by tuning ABA signaling in rice.