Pre-exposure to drought enhances resilience to recurrent drought in soybean by orchestrating H2O2 homeostasis through coordinated antioxidant and hexose metabolism

Abstract

Drought-primed soybean seedlings are able to maintain a dynamic equilibrium of hydrogen peroxide (H2O2) during subsequent severe drought, but the regulatory mechanisms remain poorly understood. To investigate this, soybean seedlings in this study were exposed to mild drought priming (0.5% PEG6000 treatment for 3, 6, or 12h) followed by severe drought (5% PEG6000) for 24h. The results showed that a 6h drought-priming (W6S) effectively established dynamic H2O2 homeostasis under severe drought, maintaining levels 16.6%–19.6% above the control and minimizing oxidative damage within 0–24h. This response was associated with the dynamic regulation of WRKY transcription factors (TFs) (GmWRKY33a/b and GmWRKY12). Their early induction promoted peroxidase and catalase gene expression and activity, while subsequent downregulation maintained H2O2 balance. At 24h, reactivation of GmWRKY33a/b and GmWRKY12 and enhanced sucrose cleavage into hexoses further supported homeostasis. In contrast, shorter (W3S) or longer (W12S) priming durations failed to induce this homeostasis and resulted in severe oxidative injury. Although lasting severe drought (12–24h) further elevated H2O2 levels, upregulated expression of WRKY33 (a, b) and WRKY12 might increase soluble sugar levels to provide more substances and energy for maintaining H2O2 homeostasis and meeting the osmotic regulation. These findings demonstrate that optimal drought priming promotes H2O2 homeostasis through WRKY-mediated transcriptional regulation and hexose metabolism, providing potential targets for improving soybean drought resilience.