Pyrazine-2-carboxylic acid maintains pummelo quality by modulating ROS homeostasis through the CgWRKY31–CgPOD52 module

Abstract

Reactive oxygen species (ROS) accumulation during postharvest senescence significantly compromises the commercial quality of ‘Sanhongmiyou’ pummelo (Citrus grandis) fruit. Transcription factors in post-harvest pomelo fruits have not been the subject of sufficient study, therefore this study aims to further analyse the molecular mechanisms of transcription factor-mediated reactive oxygen species (ROS) metabolism and lignification. This study demonstrates that pyrazine-2-carboxylic acid (PCA) treatment effectively inhibits deterioration of pummelo pulp quality. Physiological analyses indicate that PCA-treated fruits exhibited reduced lignin content and malondialdehyde accumulation compared with controls, while maintaining elevated antioxidant enzyme activities (superoxide dismutase [SOD], catalase [CAT], and peroxidase [POD]) and enhanced ascorbate-glutathione cycle efficiency. Transcriptomic analysis identified a key WRKY transcription factor (CgWRKY31) negatively correlated with ROS. Subcellular localization revealed that CgWRKY31 functions as a nuclear-localization protein. Electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter (DLR) assay demonstrated that CgWRKY31 directly activates the POD gene CgPOD52 through specific binding to its W-box element, enhancing ROS scavenging capacity. These findings establish a regulatory mechanism where PCA treatment maintains postharvest quality by CgWRKY31-mediated antioxidant enhancement, providing a promising strategy for citrus fruit preservation.