Abstract: Chilling injury caused by low temperatures severely reduces the postharvest quality and marketability of banana fruit. Although glutathione S-transferase (GST)-mediated reactive oxygen species (ROS) scavenging constitutes a core antioxidant defense against cold oxidative stress, the transcriptional and post-translational mechanisms governing this process remain largely elusive. Here, we discovered that S-glutathionylation of the WRKY transcription factor MaWRKY44 functions as a previously unknown redox switch that orchestrates a hierarchical transcriptional cascade to enhance cold tolerance. LC-MS/MS identified Cys45 and Cys199 as conserved S-glutathionylation sites of MaWRKY44. Biochemical and molecular analyses revealed a biphasic redox switch: Mild ROS triggers reversible glutathionylation to stabilize MaWRKY44 and enhance its DNA-binding capacity, whereas sustained oxidative stress drives irreversible cysteine over-oxidation that abolishes its transcriptional function. Mechanistically, we identified a C2H2 zinc finger transcription factor, MaZFP139, as a direct upstream activator of MaWRKY44, which in turn specifically binds to the W-box motifs of the MaGSTU07 promoter to drive its transcription. Transient gain- and loss-of-function assays in banana, together with stable heterologous transformation in tomato, demonstrated that the MaZFP139-MaWRKY44-MaGSTU07 cascade positively mitigates cold-triggered ROS accumulation and peel browning. Collectively, our findings uncover a multilayer transcriptional-redox module governing fruit cold tolerance, and provide potential molecular targets for improving postharvest cold storage performance in tropical fruits.

Key words: banana, C2H2 zinc finger protein, chilling injury, S-glutathionylation, WRKY transcription factor