Enhanced drought resistance in fructan-producing sugar beet

Fructans are soluble polymers of fructose that are produced by approximately 15 % of the flowering plant species. Production of bacterial fructans in tobacco has been shown previously to lead to improved biomass production under polyethylene glycol-mediated drought stress. Here, we used the same SacB gene from Bacillus subtilis to produce bacterial fructans in sugar beet (Beta vulgaris L.). The transgenic sugar beets accumulated fructans to low levels (max. 0.5 % of dry weight) in both roots and shoots. Two independent transgenic lines of fructan-producing sugar beets showed significantly better growth under drought stress than untransformed beets. Drought stressed fructan-producing plants attained higher total dry weights (+25–35 %) than wildtype sugar beet, due to higher biomass production of leaves (+30–33 %), storage roots (+16–33 %) and fibrous roots (+37–60 %). Under well-watered conditions, no significant differences were observed between the transgenic and wildtype beets. In conclusion, the introduction of fructan biosynthesis in transgenic plants is a promising approach to improve crop productivity under drought stress.