Characterization of fructan biosynthesis in big bluegrass (Poa secunda)

Most cool-season grasses contain multiple types of fructans. One exception is big bluegrass (Poa secunda Presl.). When grown under specific controlled environmental conditions it synthesizes only beta-2,6-linked fructans. This study analyzed fructan accumulations, enzyme activities and gene expression in big bluegrass. Detachment/illumination and cool treatments effectively induced the accumulation of fructans in leaf tissues. Enzyme assays indicated that 6-SST (sucrose: sucrose 6-fructosyltransferase)- and 6-SFT (sucrose: fructan 6-fructosyltransferase)-like activities were the major enzyme activities involved in fructan biosynthesis in big bluegrass leaves. A full-length cDNA of the putative 6-SFT gene was cloned using RT-PCR and RACE techniques. The deduced amino acid sequence showed 69% identity with barley 6-SFT Homology was also high with other fructosyltransferases and some invertases. The abundance of putative 6-SFT mRNA showed a coincidence with fructan accumulation and 6-SFT activity. We suggest that 6-SFT is the major enzyme involved in fructan biosynthesis in big bluegrass but it may also exhibit limited 6-SST activity.