Insight into Carbohydrate Metabolism and Signaling in Grapevine Buds during Dormancy Progression

Perennial fruit crops enter dormancy to ensure bud tissue survival during winter. However, a faster phenological advancement caused by global warming exposes bud tissue to a higher risk of spring frost damage. Tissue dehydration and soluble sugars accumulation are connected to freezing tolerance, but non-structural carbohydrates also act as metabolic substrates and signaling molecules. A deepened understanding of sugar metabolism in the context of winter freezing resistance is required to gain insight into adaptive possibilities to cope with climate changes. In this study, the soluble sugar content was measured in a cold-tolerant grapevine hybrid throughout the winter season. Moreover, the expression of drought-responsive hexose transporters VvHT1 and VvHT5, raffinose synthase VvRS and grapevine ABA-, Stress- and Ripening protein VvMSA was analyzed. The general increase in sugars in December and January suggests that they can participate in protecting bud tissues against low temperatures. The modulation of VvHT5, VvINV and VvRS appeared consistent with the availability of the different sugar species; challenging results were obtained for VvHT1 and VvMSA, suggesting interesting hypotheses about their role in the sugar-hormone crosstalk. The multifaceted role of sugars on the intricate phenomenon, which is the response of dormant buds to changing temperature, is discussed.