TaPYL-mediated chemical activation of ABA signaling in wheat enhances water productivity and reinforces carbohydrate reserves

Main conclusion Chemical activation of ABA signaling via synthetic agonists provides a reversible, high-precision strategy to optimize wheat water-use efficiency by coupling persistent antitranspirant effects with the metabolic reinforcement of carbohydrate reserves. Abstract The phytohormone abscisic acid (ABA) and its PYR/PYL/RCAR receptors are central targets for improving crop drought tolerance. In hexaploid wheat ( Triticum aestivum ), the actual number of ABA receptors (TaPYLs) has been a matter of debate, ranging from 26 to 38. This study refines this classification, demonstrating that 12 putative TaPYLs belong to the Bet v/START/Polyketide cyclase superfamily, but lack key structural features of functional ABA receptors. Indeed, structural and bioinformatic analyses confirm that their ligand-binding cavities cannot accommodate ABA and lack key residues for ABA binding. As a result, whereas TaPYL1, TaPYL4, and TaPYL6 mediate ABA-dependent inhibition of PP2Cs, the TraesCS3B02G160200 putative receptor does not. Therefore, wheat has only 26 potential TaPYL ABA receptors. Given the biotechnological potential of the ABA pathway, we investigated its chemical activation using the synthetic receptor agonist iSB09. This compound is perceived by highly expressed TaPYLs and induces a more persistent antitranspirant effect than exogenous ABA. Plants treated with iSB09 consumed approximately 25% less water over 15 days without incurring a biomass penalty, resulting in significantly higher water productivity. Beyond regulating transpiration, agonist treatment increased fructan and starch levels compared with controls. A short-term RNA-seq experiment revealed that ABA treatment triggers a coordinated reprogramming of carbohydrate metabolism genes, including the upregulation of genes involved in the biosynthesis of protective osmolytes (fructans and raffinose) and starch, coupled with the downregulation of genes involved in starch mobilization. In summary, this work provides a clarified census of the wheat TaPYL family, establishes chemical activation of ABA signaling as an effective strategy to boost water-use efficiency, and suggests that the reinforcement of reserve and protective carbohydrate pathways is a key metabolic mechanism linked to ABA signaling.