High production of plant type levan in sugar beet transformed with timothy (Phleum pratense) 6-SFT genes

Levan, a type of fructan, is an oligomer or polymer with mainly a β(2,6)-linked fructose chain attached to sucrose. We introduced two timothy genes, PpFT1 and PpFT2, coding for two homologous sucrose:fructan 6-fructosyltransferases into sugar beet. Sugar beet produces a high concentration of sucrose, a starting substrate in fructan synthesis, in the root. Among transgenic T1 lines, we obtained sugar beet transformants that accumulated large amounts of β(2,6)-linked levans (about 20 to 75 mg g−1 FW) in the roots. The transformed sugar beet plants possessing PpFT1 or PpFT2 produced linear levans with different degrees of polymerization (DP). Namely, the PpFT1 transformants accumulated mainly high DP levans including those with DP > 40, while the PpFT2 transformants accumulated levans with DP between 3 and 40. Chromatograms showed that PpFT2 produces pure β(2,6)-linked linear levans compared with fructans synthesized by PpFT1. These levans belong to the high DP class of plant fructans, but have much shorter DP than that of levans generally produced by microorganisms.