Modification of the total soluble sugar content of the C4 grassPaspalum notatumexpressing the wheat-derived sucrose:sucrose 1-fructosyltransferase and sucrose:fructan 6-fructosyltransferase genes

Abstract

Fructans are water-soluble fructose oligomers and polymers that are accumulated in many plants, especially the C3 temperate grasses. Fructan accumulation enhances cold and drought tolerance in grasses, and the increased soluble carbohydrates improve forage quality, especially the nutritional value animals can gain from these grasses. The C4 grasses yield high biomass but their inability to accumulate fructans coupled with their low water-soluble carbohydrate (WSC) content are limiting factors for the forage quality of these grasses. The aim of this study was to produce fructans and increase the total soluble sugar content by introducing and expressing fructan biosynthesis genes in a C4 grass, bahiagrass (Paspalum notatum Flugge). Using particle bombardment, we transformed bahiagrass with a wheat-derived sucrose:sucrose 1-fructosyltransferase (1-SST) gene and a sucrose:fructan 6-fructosyltransferase (6-SFT) gene, both of which were regulated by the cauliflower mosaic virus (CaMV) 35S promoter. Transcripts of the 1-SST and 6-SFT genes were detected in six out of 12 transgenic plants carrying both genes. Transgenic bahiagrass plants expressing the 1-SST and 6-SFT genes accumulated 1-kestose and nystose. Although further polymerization of fructose units by 6-SFT activity was not detected in transgenic plants, the total soluble sugar content increased. These results suggest that transgenic bahiagrass plants expressing wheat fructosyltransferase genes created a new metabolic pathway for fructan biosynthesis, which is an important requirement for producing fructans in C4 forage grasses with the objective of increasing the total soluble sugar content of these plants. This is the first report of introducing plant-derived fructosyltransferases with the goal of increasing fructan accumulation in C4 forage grasses.