Physiological and transcriptomic analysis of IAA-induced antioxidant defense and energy metabolism in postharvest papaya fruit

Papaya ( Carica papaya L.) is a tropical fruit with considerable nutritional value. However, its postharvest shelf life is severely limited by rapid ripening, senescence, oxidative stress, and energy depletion. In this study, we investigated the effects of exogenous indole-3-acetic acid (IAA) treatment on the antioxidant capacity and energy metabolism of papaya fruit during postharvest storage. IAA treatment significantly enhanced the antioxidant defense system by increasing the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). IAA promoted the accumulation of non-enzymatic antioxidants, including ascorbic acid (AsA), anthocyanins, flavonoids, and total phenols. IAA treatment increased the activities of polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL), contributing to the effectiveness of antioxidant system. IAA treatment improved energy metabolism by upregulating key enzymes involved in the pentose phosphate pathway (PPP) and the tricarboxylic acid (TCA) cycle, including NAD kinase (NADK), glucose-6-phosphate dehydrogenase (G6PDH), and 6-phosphogluconate dehydrogenase (6PGDH), succinic dehydrogenase (SDH), cytochrome c oxidase (CCO), proton-ATPase (H + -ATPase), supporting NADPH regeneration and ATP synthesis. Transcriptomic analysis showed that IAA modulated the expression of genes associated with the oxidative stress response and energy metabolism, including CpGSTF9 , CpPOD61 , CpAAC , CpPAS2B , CpSWEET1 , CpbHLH137 , and CpMYB61 . These findings suggest that IAA enhances both the antioxidant and energy metabolic pathways to mitigate oxidative damage and delay ripening, providing a promising strategy for improving the postharvest quality and storage life of papaya. • IAA treatment enhances antioxidant capacity and reduces oxidative stress in postharvest papaya. • IAA promotes energy metabolism by upregulating key enzymes in the PPP and TCA cycle. • Transcriptomic analysis identifies genes like CpGSTF9 , CpPOD61 , and CpMYB61 as regulators of oxidative stress and energy metabolism in papaya.