Capping invertase activity by its inhibitor: roles and implications in sugar signaling, carbon allocation, senescence and evolution.

Since the initial biochemical study of a putative invertase inhibitor half a century ago, it has remained as a puzzle as whether such an inhibitory protein indeed limits invertase activity in vivo and, if it does, what is the developmental or physiological significance of such an interaction? Recently, we demonstrated that an invertase inhibitor, INVINH1, specifically inhibited cell wall invertase activity in tomato and Arabidopsis. Silencing INVINH1 expression in tomato released a significant amount of extra cell wall invertase activity. This posttranslational elevation of invertase activity resulted in a blockage of ABA-induced leaf senescence and an increase in fruit sugar levels and seed weight. Here, we discuss the implication of the findings and propose a model that the invertse inhibitor may act as a key modulator in controlling leaf longevity and seed development to ensure success during plant evolution. This may be achieved by optimizing carbon and nitrogen allocation and sugar signaling via interaction between invertase and inhibitor. The discoveries open up exciting new areas for exploring fundamental questions in sugar signaling, carbon allocation and plant development as well as avenues for improving crop productivity.