Transcriptome analysis reveals a regulatory role of hexokinase in kiwifruit postharvest softening

Kiwifruit postharvest softening properties were evaluated upon treatment with 10 mM D(+)-glucosamine hydrochloride (GAH, a hexokinase inhibitor). GAH effectively attenuated the loss of firmness, decreases of starch and protopectin contents, increase in soluble pectin, and reduction in sugar content, thereby promoting fruit quality. Transcriptome sequencing indicated significant enrichment of differentially expressed genes (DEGs) in those related to cell wall organization, carbohydrate metabolic processes, and protein phosphorylation. Weighted gene co-expression correlation network analysis revealed that genes encoding β -amylase ( BAM1–3/7–8 ), hexokinase ( HXK4 ), fructokinase ( FRK3/4 ), polygalacturonase ( PG1 ), and pectate lyase ( PEL ) were considered key structural genes highly correlated with firmness. Furthermore, real-time quantitative PCR and correlation network analysis revealed that HXK4 expression significantly negatively correlated with that of calmodulin-binding transcription activator ( CMTA5 ) and transcription factor ( WRKY1b ), whereas the two transcription factors and nine key structural genes were significantly positively correlated. Transient overexpression analysis suggested that AcHXK4 may perform dual roles, depending on either the catalytic activity or signaling function, and inhibit expression levels of WRKY1b, CMTA5 , and their downstream genes related to starch and pectin degradation, subsequently delaying kiwifruit postharvest softening. These results offer novel perspectives on the regulatory mechanisms implicated in kiwifruit postharvest softening. • Effect of D(+)-glucosamine on postharvest kiwifruit softening was studied. • Glucosamine treatment delayed the loss of fruit firmness, promoting fruit quality. • HXK4 was among the differentially expressed genes in control and treated fruits. • HXK4 overexpression revealed glucose-dependent effects of hexokinase.