Comparative transcriptomic analysis provides novel insights on the hormonal regulation of postharvest apples under cold storage

Abstract

Postharvest storage is a crucial phase during which fruit undergoes ripening and senescence. This study is based on the hypothesis that ethylene-auxin interactions play a significant role in determining apple storage life and quality during the postharvest period. To test this hypothesis, fruit flesh firmness and hormone levels were analyzed alongside transcriptomic changes observed through RNA sequencing. A comprehensive investigation of hormone metabolism-related gene expression across the whole transcriptome was conducted in 'Golden Delicious' apples over a six-month storage period to elucidate the molecular mechanisms underlying postharvest ripening and senescence. Understanding changes in the ripening process was facilitated by pretreatment with ethylene, the ethylene inhibitor 1-methylcyclopropene (1-MCP), auxin, and the auxin inhibitor 1-N-naphthylphthalamic acid (NPA) prior to cold storage. The results demonstrated that the auxin inhibitor suppressed ethylene production along with auxin levels, while the ethylene inhibitor suppressed auxin levels together with ethylene production throughout all storage periods. Findings also revealed that ethylene and auxin hormones regulate key metabolic processes associated with apple ripening during storage. Additionally, many transcriptional regulatory genes involved in hormone signaling and metabolism, such as AIL5, ABI3, AP2, ERF-011, NAC, RAP210, and REVEILLE, exhibited high activity during storage. Furthermore, this study revealed the high expression levels of ABC transporter and LRR receptor protein kinase for the first time in apples under storage conditions. These findings provide deeper insights into the physiological and molecular changes occurring in climacteric fruit during postharvest storage.