A small peptide modulates stomatal control via abscisic acid in long-distance signalling.

Mammalian peptide hormones propagate extracellular stimuli from sensing tissues to appropriate targets to achieve optimal growth maintenance ¹ . In land plants, root-to-shoot signalling is important to prevent water loss by transpiration and to adapt to water-deficient conditions ^{2, 3} . The phytohormone abscisic acid has a role in the regulation of stomatal movement to prevent water loss ⁴ . However, no mobile signalling molecules have yet been identified that can trigger abscisic acid accumulation in leaves. Here we show that the CLAVATA3/EMBRYO-SURROUNDING REGION-RELATED 25 (CLE25) peptide transmits water-deficiency signals through vascular tissues in Arabidopsis, and affects abscisic acid biosynthesis and stomatal control of transpiration in association with BARELY ANY MERISTEM (BAM) receptors in leaves. The CLE25 gene is expressed in vascular tissues and enhanced in roots in response to dehydration stress. The root-derived CLE25 peptide moves from the roots to the leaves, where it induces stomatal closure by modulating abscisic acid accumulation and thereby enhances resistance to dehydration stress. BAM receptors are required for the CLE25 peptide-induced dehydration stress response in leaves, and the CLE25-BAM module therefore probably functions as one of the signalling molecules for long-distance signalling in the dehydration response.

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