A leucine-rich-repeat receptor-like kinase SERL1 phosphorylates and stabilizes OsALDH2B1 to promote alkaline tolerance and grain size in rice.

Enhancing crop resilience to guarantee stable, high yields under adverse conditions has long been a central goal of rice breeding, but it remains challenging because of inherent trade-offs. Here, we show that the transcriptional activity of the aldehyde-dehydrogenase OsALDH2B1 simultaneously increases grain length and alkaline tolerance. Upon alkali stress, the plasma-membrane leucine-rich-repeat receptor-like kinase SERL1 phosphorylates OsALDH2B1 at Thr-481, thereby blocking its 26S-proteasome-mediated degradation. Stabilized OsALDH2B1 directly represses GS3, a negative regulator of both grain size and alkaline tolerance, and activates all three catalase genes, leading to reduced hydrogen-peroxide (H2O2) accumulation. OsALDH2B1 over-expression enlarged grains and raised grain yield under field alkalinity, whereas osaldh2b1 mutants were hypersensitive. CRISPR knockouts of SERL1 or the catalase genes phenocopied these defects, confirming that the SERL1-OsALDH2B1 module constitutes an integrated signaling axis that links membrane perception to nuclear reprogramming through GS3 repression and catalase activation. This dual-purpose circuit provides an immediate, breeder-friendly target for high-yield, alkaline-resilient rice.