Plasma membrane CYBDOM proteins catalyse apoplastic AsA regeneration and interact with RbohD to activate autophagy and drought tolerance in plants.

Autophagy and apoplastic ascorbic acid (AsA) play important roles in plant drought tolerance. However, the trans-plasma membrane transport of AsA and its association with autophagy during drought stress are unclear. Here we report an AsA-induced autophagy pathway in plants, wherein plasma-membrane-located cytochrome b561 and DOMON domain (CYBDOM) proteins play positive roles. CYBDOM proteins from the resurrection plant Boea hygrometrica (BhDB) and Arabidopsis (AtDB1) can transport electrons across the plasma membrane using intracellular AsA as an electron donor and apoplastic monodehydroascorbic acid or Fe as electron acceptors in Xenopus laevis oocytes. Increased apoplastic AsA, autophagy and drought tolerance are observed in BhDB- and AtDB1-overexpressing Arabidopsis compared with the wild type. CYBDOM proteins interact with respiratory burst oxidase homologue D (RbohD), which serves as the adaptor to bind autophagy related gene 8 protein (ATG8) and cargo protein for autophagic degradation. AsA increases AtDB1 protein level and its interaction with RbohD. Together, the AsA-activated CYBDOM-RbohD synergy to induce autophagy suggests a novel mechanism in plant drought and desiccation tolerance.