Local peptide signalling induces stomatal closure under drought stress

In response to drought stress, land plants close their stomata to minimize transpiration. This action precedes a gradual accumulation of the stress hormone abscisic acid (ABA) that enhances plant drought tolerance. However, the molecular mechanisms that cause the time lag between the onset of stomatal closure and ABA accumulation and coordinate these two phases remain unexplained. Here, we found that Arabidopsis thaliana loss-of-function CLAVATA3/ENDOSPERM SURROUNDING REGION 5 (CLE5) mutants are less tolerant to drought. The CLE5 dodecapeptide (CLE5p) acts as a local signal to induce stomatal closure by binding to the LEUCINE-RICH REPEAT RECEPTOR-LIKE KINASE (LRR-RLK) receptor complex, BARELY ANY MERISTEM 1 (BAM1)-GUARD CELL HYDROGEN PEROXIDE-RESISTANT 1 (GHR1), in guard cells. The BAM1-GHR1-CLE5p module directly phosphorylates two SNF1-related protein kinases, OPEN STOMATA1 (SRK2E) and SRK2D, the central regulators of drought responses in plants, to regulate stomatal movement and drought-responsive gene expression without stimulating ABA biosynthesis or ROS accumulation. Our findings mark a critical step in understanding how plants promptly counteract environmental stresses. The CLEp-LRR-RLK signalling components are highly conserved across plant phyla, suggesting that peptide-mediated rapid stomatal closure is a widespread survival strategy and can be exploited to generate drought-resistant crops.