Expression of the VvMYB60 Transcription Factor Is Restricted to Guard Cells and Correlates with the Stomatal Conductance of the Grape Leaf

The modulation of stomatal activity is a relevant trait in grapes, as it defines the isohydric/ anysohydric behavior of different cultivars and directly affects water-use efficiency and drought resistance of vineyards. The grape transcription factor VvMYB60 has been proposed as a transcriptional regulator of stomatal responses based on its ectopic expression in heterologous systems. Here, we directly addressed the cellular specificity of VvMYB60 expression in grape leaves by integrating independent approaches, including the qPCR analysis of purified stomata and the transient expression of a VvMYB60 promoter: GFP fusion. We also investigated changes in the VvMYB60 expression in different rootstocks in response to declining water availability. Our results indicate that VvMYB60 is specifically expressed in guard cells and that its expression tightly correlates with the level of stomatal conductance (gs) of the grape leaf. As a whole, these findings highlight the relevance of the VvMYB60 regulatory network in mediating stomatal activity in grapes.