GPX Knockdown Is Associated with Altered Redox Homeostasis, Plant Development, and DNA Methylation-Related Profiles in Rice

Background: Glutathione peroxidases (GPXs) regulate peroxide detoxification and redox signaling, but their relationship with DNA methylation remains unclear in Oryza sativa. This study evaluated whether silencing mitochondrial GPX1 and GPX3 is associated with changes in growth, antioxidant activity, and DNA methylation-related profiles. Methods: Non-transformed plants (NT) and five GPX-silenced lines were evaluated in a randomized complete block design. Morphophysiological traits, antioxidant enzyme activities, total 5-methylcytosine content, and methylation-sensitive restriction profiles were analyzed. Results: GPX silencing impaired early establishment and significantly affected flowering time and leaf, root, seed, and total biomass. Total dry biomass decreased by 62.1% in the most affected GPX1 lines and by 29.2% in GPX3 lines relative to NT plants. Root biomass declined by up to 86.1%, and flowering was delayed by up to 30.7 days. Genotype significantly affected GPX-associated and glutathione reductase activities, whereas no significant genotype effects were detected for catalase, ascorbate peroxidase, or superoxide dismutase activities. GPX-associated and glutathione reductase activities were strongly correlated (r = 0.85, p < 0.001), consistent with selective alteration of GPX-associated and glutathione-linked redox metabolism. Total 5-methylcytosine content decreased by 41–42% in GPX-silenced groups. However, increased McrBC digestion and unchanged HpaII/MspI profiles indicated that methylation-related changes were nonuniform and depended on the genomic sites recognized by each enzymatic assay. Conclusions: These findings show that mitochondrial GPX knockdown is associated with impaired rice growth and reproductive development, as well as with altered total 5-methylcytosine content and restriction-sensitive methylation profiles, suggesting a potential relationship among redox homeostasis, developmental regulation, and epigenetic plasticity that requires further validation using locus-resolved and mechanistic approaches.