Expression profile of genes involved in sugar metabolism during 'Donghong' kiwifruit postharvest ripening

Once fruit were commercially harvested from vines, starch is degraded into soluble sugars such as sucrose, glucose, and fructose, which determine kiwifruit's nutritional and commercial quality. Glucose and fructose are the main sugars in mature kiwifruit, followed by sucrose. The expression of genes related to sugar metabolism during kiwifruit postharvest ripening is little-studied, so we identified a set of putative kiwifruit sugar metabolism genes containing three cell wall inverters (CWINVs), five fructokinases (FKs), five hexokinases (HXKs), five sucrose phosphate synthases (SPSs), six sucrose synthases (SUSs), and fourteen neutral invertases (NINVs). Phylogenetic analyses of Arabidopsis thaliana, kiwifruit, and tomato identified orthologous groups among them. AcCWINV1 and AcNINV3 transcription decreased as fruit sugar levels increased, but increased after 1-methylcyclopropene (1-MCP) application. AcFK1, AcFK2, AcHXK1, AcHXK2, AcSPS1, AcSPS5, AcSUS2, and AcNINV10 exhibited fruit-expressed, up-regulated profiles during postharvest ripening and were inhibited by 1-MCP, suggesting that they are involved in fruit sugar accumulation. Our results elucidate the genomic organizations, evolutionary characteristics, and expression profiling of sugar metabolism genes during kiwifruit postharvest stages, paving the way for further functional verification of sugar metabolism genes.