JA-mediated H₂O₂ and ABA signaling enhances root hydraulic conductance in cotton under partial root-zone irrigation

Partial root-zone irrigation (PRI) is a water-saving technique that improves water use efficiency by inducing physiological adaptations. While abscisic acid (ABA)-mediated stomatal closure from dried roots conserves water ("reducing outflow"), hydraulic compensation in the hydrated roots ("enhancing inflow") is critical for maintaining plant water balance. The signaling network, particularly the interplay between jasmonic acid (JA), ABA, and hydrogen peroxide (H₂O₂), regulating this compensation remains elusive.

To dissect this signaling network, cotton seedlings were grown in a stratified rhizobox system simulating PRI. Exogenous JA, ABA, H₂O₂,and their biosynthesis inhibitor 5,8,11,14-eicosatetraynoic acid (ETYA), fluridone and diphenyleneiodonium chloride (DPI) were employed to establish causality. Physiological (root water status, hydraulic conductance L), JA, ABA and H₂O₂ content, and the expression level of their biosynthesis genes and GhPIP genes in distinct root zones were analyzed.

Compared to uniformly irrigated or droughted roots, hydrated roots under PRI exhibited significantly enhanced root L and upregulated expression of plasma membrane intrinsic protein genes (GhPIP1;5, GhPIP2;8). This was associated with elevated JA/JA-Ile and H₂O₂ levels in the hydrated zone. Exogenous JA and H₂O₂ mimicked these effects, while their inhibitors suppressed them. JA was found to be upstream, positively regulating H₂O₂ production and modulating local ABA homeostasis. ABA affected root L without altering PIP transcript levels. Complementation assays confirmed the specificity of the JA-H₂O₂-PIP pathway.

The enhanced hydraulic conductance in the hydrated roots under PRI is an active process orchestrated by a JA-centered signaling network. JA promotes H₂O₂ accumulation, which up-regulates PIP expression, and fine-tunes ABA levels for potential post-translational regulation. This study elucidates the "enhanced inflow" mechanism in PRI, providing insights for optimizing water-saving irrigation strategies.