StInvInh2 as an inhibitor of Stvac INV 1 regulates the cold‐induced sweetening of potato tubers by specifically capping vacuolar invertase activity

Summary Reducing sugar ( RS ) accumulation in cold‐stored potato tubers, known as cold‐induced sweetening ( CIS ), is a crucial factor causing unacceptable colour changes and acrylamide formation of fried products. The activity of vacuolar invertase (Stvac INV 1) is proved important for the CIS process, and invertase inhibitors are speculated to play roles in the post‐translational regulation of Stvac INV 1 activity. In our previous research, two putative inhibitors (StInvInh2A and StInvInh2B) of Stvac INV 1 were implied to be involved in potato CIS . Here, we further reported that StInvInh2A and StInvInh2B had similar function that specifically inhibited Stvac INV 1 activity in potatoes. The genetic transformation of these inhibitor genes in potatoes by overexpression in CIS ‐sensitive and RNA i‐silenced in CIS ‐resistant genotypes showed that Stvac INV 1 activity was strongly regulated by alteration of the transcripts of the inhibitors without impacting on the expression of Stvac INV 1 . A negative power relationship was found between the transcripts of the inhibitors and Stvac INV 1 activity, suggesting 1) a transcriptional determination of the inhibitory capacity of StInvInh2A and StInvInh2B and 2) a significant inhibitory role of these inhibitors in post‐translational modulation of Stvac INV 1. The results also demonstrated that depression of Stvac INV 1 activity through overexpression of StInvInh2A and StInvInh2B weakened accumulation of RS and acrylamide in cold‐stored tubers and consequently improved the chip quality. The present research strongly suggest that both StInvInh2A and StInvInh2B function as inhibitors of Stvac INV 1 and play similar roles in regulating potato CIS by capping Stvac INV 1 activity. These inhibitors could be novel genetic resources applicable for improving quality of potato processing products.