The Sweet Side of Inhibition: Invertase Inhibitors and their Importance in Plant Development and Stress Responses

Cell wall and vacuolar invertases are important regulators of plant growth; they also participate in stress responses and modulate sink-source relationships and sugar-related signaling. Their physiological importance necessarily requires that their activity be tightly controlled, either by transcriptional or post-transcriptional mechanisms, to ensure an appropriate development of the plant. Knowledge regarding the way these enzymes are controlled in planta has been gradually increasing, including novel information regarding the regulatory role played by a well-known family of small invertase inhibitor proteins. This review complements a previous compilation dedicated to these inhibitory proteins [1]. It will concentrate on recent reports describing the spatiotemporal impact that invertase inhibitors appear to have in several aspects of plant growth and development, in stress responses and in processes that have a direct influence on food processing. Hitherto unknown aspects regarding their mode of action that were recently uncovered will be described, such as co-localization and physical interaction with their target enzymes detected in planta and direct participation in (a)biotic stress responses and in the senescence process. The utilization of alternative splicing to increase the diversity and functionality of invertase inhibitors to facilitate the repression of the unwanted cold-induced sweetening process in potato tubers, will also be discussed, in addition to a description of the increasing body of evidence showing the biotechnological potential that the manipulation of invertase inhibitor levels in plants might have on the improvement of crop productivity and fruit quality traits.