Sugar metabolism mediates freezing tolerance in grapevines: novel approach and recent advances

Abstract

Grape acreage has been expanding rapidly in the cold regions of the U.S. However, the economic sustainability of the grape industry is hampered by freezing damage. It has long been established that sugars play a role in mediating freezing tolerance (FT) in grapes. To advance our understanding of the role of sugar metabolism in mediating FT, we utilized a two-pronged approach. First, since the accumulation of specific sugars strongly correlated with FT in cold-hardy grape genotypes, it was hypothesized that FT in the cold-sensitive grape genotypes can be improved by metabolically engineering grapes to increase sugar accumulation. Grape embryogenic tissues were transformed with gene constructs designed to increase the accumulation of specific “frost protectant sugars”. Gene introduction and expression were confirmed by PCR and metabolite analysis, respectively. Second, as we have previously demonstrated that application of exogenous abscisic acid (ABA) increased the FT of grapevines, we hypothesized that ABA regulates sugar metabolism. Greenhouse-grown grape cultivars were sprayed with ABA and compared to untreated (control) vines over a two-week period. Bud FT, total and most individual sugars increased over time in both control and treated vines, but some sugars were higher in treated than in control vines. The findings from this research have increased our knowledge of the regulatory roles of ABA and sugars on the early cold acclimation responses, and will ultimately help develop new strategies to mitigate freezing damage and thus enhance the economic and environmental sustainability of grape production in cold regions.