In an era when climate change threatens global agriculture, understanding the molecular mechanisms underpinning plant drought tolerance is more urgent than ever. A recent groundbreaking study sheds light on a hitherto unexplored pathway that couples ascorbic acid (AsA), a well-recognized antioxidant, with autophagy, a conserved cellular degradation process, to enhance drought resilience in plants. This newly characterized mechanism hinges on a unique group of plasma membrane proteins, known as CYBDOM, which orchestrate extracellular AsA regeneration and signal transduction to activate autophagy, culminating in improved drought tolerance.
Ascorbic acid, also known as vitamin C, is crucial in plant physiology, especially under stress conditions. While its intracellular antioxidant functions have been extensively studied, its role and movement across the plasma membrane, specifically in the apoplastic space under drought stress, have remained obscure. Equally enigmatic has been the interplay between AsA and autophagy — a cellular recycling process that promotes survival under nutrient deprivation and various abiotic stresses. The study in question addresses this gap deftly, unveiling a direct mechanistic link mediated by CYBDOM proteins.
The researchers focused on plasma membrane-localized cytochrome b561 and DOMON domain (CYBDOM) proteins, which were initially identified in the resurrection plant Boea hygrometrica, known for its remarkable ability to survive extreme desiccation. Parallel homologs were studied in the model organism Arabidopsis thaliana, facilitating comprehensive functional analyses. These CYBDOM proteins, designated BhDB in B. hygrometrica and AtDB1 in Arabidopsis, possess the unique ability to shuttle electrons across the plasma membrane by leveraging intracellular AsA as an electron donor.
Using Xenopus laevis oocytes as a heterologous expression system, the team demonstrated that BhDB and AtDB1 efficiently transport electrons to apoplastic electron acceptors, such as monodehydroascorbic acid (MDHA) and Fe³⁺ ions. This electron transport capability facilitates the regeneration of apoplastic AsA, thereby sustaining an extracellular antioxidant buffer that is critical under drought-induced oxidative stress.
Remarkably, overexpressing either BhDB or AtDB1 in Arabidopsis plants resulted in heightened apoplastic AsA levels, concomitant with increased autophagic activity and improved drought tolerance phenotypes. These transgenic plants displayed more robust physiological parameters during controlled drought experiments compared to wild-type controls, underscoring the functional relevance of CYBDOM proteins in managing oxidative stress and maintaining cellular homeostasis through autophagy activation.
Delving deeper into the molecular players, the researchers discovered that CYBDOM proteins physically interact with the respiratory burst oxidase homologue D (RbohD), a NADPH oxidase responsible for reactive oxygen species (ROS) production at the plasma membrane. This interaction was pivotal, as RbohD acted as an adaptor linking CYBDOM proteins to the autophagy machinery.
Specifically, RbohD was found to bind autophagy-related protein 8 (ATG8), a key component involved in autophagosome formation and selective cargo recognition during autophagy. The CYBDOM–RbohD–ATG8 axis, therefore, constitutes a novel signaling hub, whereby the extracellular antioxidant status, modulated by AsA, influences intracellular autophagic responses via ROS-mediated pathways.
Intriguingly, exogenous application of AsA was shown to elevate AtDB1 protein abundance and reinforce its association with RbohD, suggesting that AsA functions not only as a redox buffer but also as a signaling ligand that modulates the stability and interaction dynamics of CYBDOM proteins at the plasma membrane. This AsA-induced stabilization enhances the downstream activation of autophagy, positioning AsA as a central regulator of stress-induced cellular recycling.
This study breaks new ground by connecting redox processes in the apoplast with intracellular autophagy pathways, mediated via plasma membrane electron transport systems and NADPH oxidases. Such integration of extracellular and intracellular signaling networks reveals an elegant strategy that plants employ to sense and mitigate drought-induced oxidative damage.
The relevance of CYBDOM protein function to desiccation tolerance was elegantly underscored by the resurrection species Boea hygrometrica. Resurrection plants possess the extraordinary ability to survive near-complete water loss and resume normal physiology upon rehydration. The presence and activity of BhDB in B. hygrometrica provide a crucial biochemical underpinning to this capability, establishing CYBDOM-mediated AsA regeneration and autophagy induction as a survival hallmarks.
From an evolutionary perspective, the conservation of CYBDOM proteins from resurrection plants to Arabidopsis suggests that this electron transport-autophagy coupling mechanism may be widespread among vascular plants, providing opportunities for biotechnological exploitation to engineer drought-resilient crops.
One of the most exciting aspects of this research lies in its potential translational applications. By manipulating CYBDOM expression or activity, it may be possible to fortify crop plants against the increasing frequency and severity of drought episodes predicted under climate change scenarios. Such strategies would complement existing approaches targeting stomatal regulation and osmolyte synthesis, adding a critical layer of redox and autophagic control.
Moreover, the elucidation of the CYBDOM–RbohD interactome opens avenues to discover small molecules or peptides that can modulate this interaction, offering novel agrochemical tools to induce autophagy and strengthen plant resilience without genetic modification.
Autophagy itself is emerging as a multifaceted process beyond mere nutrient recycling. Its role in selective degradation of damaged organelles, protein aggregates, and even invading pathogens reflects a sophisticated quality control system intertwined with stress signaling networks. The identification of CYBDOM and RbohD as key mediators feeding into the autophagic machinery enriches our understanding of how plants integrate external environmental cues with internal degradation pathways.
The reactive oxygen species generated via RbohD activity traditionally have been viewed as damaging by-products; however, this research reinforces the paradigm of ROS as signaling molecules that orchestrate adaptive responses. The controlled production of ROS by NADPH oxidases, modulated by electron transfer from AsA via CYBDOM proteins, exemplifies a finely tuned redox relay system.
The detailed mechanistic insights presented in this study also challenge researchers to explore how other redox-active components at the plasma membrane might influence autophagy and stress tolerance. It raises questions about the coordination between different electron transport chains and their spatial-temporal regulation under fluctuating environmental stresses.
From a methodological standpoint, the integration of heterologous electrophysiology assays in Xenopus oocytes with in planta molecular biology and physiology represents a powerful interdisciplinary approach that could be emulated in future studies dissecting membrane protein functions.
Overall, this illuminating research not only advances fundamental plant biology but also holds practical promise for enhancing crop resilience in a warming world. By unmasking the AsA-activated CYBDOM–RbohD synergy that triggers autophagy, the study opens a fresh frontier in our quest to fortify plants against drought—a pressing challenge of the 21st century.
Subject of Research: Plant molecular mechanisms underlying drought tolerance, specifically the role of plasma membrane CYBDOM proteins in ascorbic acid regeneration and autophagy activation.
Article Title: Plasma membrane CYBDOM proteins catalyse apoplastic AsA regeneration and interact with RbohD to activate autophagy and drought tolerance in plants.
Article References:
Chen, X., Jin, S., Du, H. et al. Plasma membrane CYBDOM proteins catalyse apoplastic AsA regeneration and interact with RbohD to activate autophagy and drought tolerance in plants. Nat. Plants (2025). https://doi.org/10.1038/s41477-025-02057-y
Image Credits: AI Generated
