VvGOLS1 and VvHsfA2 are Involved in the Heat Stress Responses in Grapevine Berries

Among various environmental factors, temperature is a major regulator affecting plant growth, development and fruit composition. Grapevine is the most cultivated fruit plant throughout the world, and grapes are used for wine production and human consumption. The molecular mechanisms involved in grapevine tolerance to high temperature, especially at the fruit level, are poorly understood. To better characterize the sensitivity of berries to the microenvironment, high temperature conditions were locally applied to Vitis vinifera Cabernet Sauvignon clusters. Two genes, VvGOLS1 and VvHsfA2, up-regulated by this treatment, were identified and further characterized. The expression profile of VvGOLS1 correlated positively with galactinol accumulation in heat-stressed berries. However, no galactinol derivatives, such as raffinose and stachyose, accumulated upon heat stress. Heterologous expression of VvGOLS1 in Escherichia coli showed that it encodes a functional galactinol synthase. Transient expression assays showed that the heat stress factor VvHsfA2 transactivates the promoter of VvGOLS1 in a heat stress-dependent manner. Taken together, our results highlight the intrinsic capacity of grape berries to perceive heat stress and to initiate adaptive responses, suggesting that galactinol may play a signaling role in these responses.