ISOLATION AND CHARACTERISATION OF FRUCTAN BIOSYNTHESIS GENES FROM FORAGE GRASSES

Plant Biotechnology Centre,Agriculture Victoria,La Trobe University and CRC for Molecular Plant Breeding, Bundoora, Victoria 3083, Australia

Fructans are polyfructose molecules produced as a major soluble storage carbohydrate in the temperate grasses. Plant fructans vary in degree of polymerization and linkage type, depending on species and environmental conditions. Apart from their role in photosynthate partitioning, fructan accumulation has been associated with the plant response to the environmental stresses such as drought and cold. Biosynthesis of complex fructans prevalent in grasses involves three enzymes; sucrose:sucrose 1-fructosyltransferase (1-SST); fructan:fructan 1-fructosyltransferase (1-FFT); and sucrose:fructan 6-fructosyltransferase (6-SFT). Our research is aimed at a genetic dissection of fructan biosynthesis in temperate grasses and the manipulation of fructan metabolism in plants for enhanced tolerance to abiotic stress and enhanced levels of soluble carbohydrates. A seedling cDNA library was screened for the isolation of cDNAs encoding perennial ryegrass (Lolium perenne L.) fructosyltransferases. Full length cDNA clones encoding perennial ryegrass 6-SFT (Lp6SFT1) and 1-SST (Lp6SFT2) homologues were obtained and sequenced. Expression profiles and gene organization of Lp6SFT1 and Lp6SFT2 were determined. Sense and antisense vectors using Lp6SFT1 and Lp6SFT2 sequences under control of constitutive promoters were generated and transgenic plants were produced for functional analyses. This will further our understanding of the biosynthesis and function of fructans in grasses towards the production of transgenic pasture grasses with enhanced nutritive value and tolerance to abiotic stress.