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

ABSTRACT 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 (H 2 O 2 ) 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.