Fructan:fructan 1-fructosyltransferase, a key enzyme for biosynthesis of graminan oligomers in hardened wheat.
Fructans play important roles not only as a carbon source for survival under persistent snow cover but also as agents that protect against various stresses in overwintering plants. Complex fructans having both beta-(2,1)- and beta-(2,6)-linked fructosyl units accumulate in wheat (Triticum aestivum L.) during cold hardening. We detected fructan: fructan 1-fructosyltransferase (1-FFT; EC 2.4.1.100) activity for catalyzing the formation and extension of beta-(2,1)-linked fructans in hardened wheat tissues, cloned cDNAs (wft3 and wft4) of 1-FFT, and analyzed the enzymatic properties of a wft3 recombinant protein (Wft3m) produced by yeast. Wft3m transferred beta-(2,1)-linked fructosyl units to phlein, an extension of sucrose through beta-(2,6)-linked fructosyl units, as well as to inulin, an extension of sucrose through beta-(2,1)-linked fructosyl units, but could not efficiently synthesize long inulin oligomers. Incubation of a mixture of Wft3m and another recombinant protein of wheat, sucrose:fructan 6-fructosyltransferase (6-SFT), with sucrose and 1-kestotriose produced fructans similar to those that accumulated in hardened wheat tissues. The results demonstrate that 1-FFT produces branches of beta-(2,1)-linked fructosyl units to phlein and graminan oligomers synthesized by 6-SFT and contributes to accumulation of fructans containing beta-(2,1)- and beta-(2,6)-linked fructosyl units. In combination with sucrose:sucrose 1-fructosyltransferase (1-SST; EC 2.4.1.99) and 6-SFT, 1-FFT is necessary for fructan synthesis in hardened wheat.
Kawakami
Akira
A
Laboratory of Fungal Disease, Department of Plant Pathology, National Agricultural Research Center, Kannondai, Tsukuba, Ibaraki 305-8666, Japan. akirak@affrc.go.jp
Yoshida
Midori
M
D000595:Amino Acid Sequence; D002236:Carbohydrate Conformation; D050260:Carbohydrate Metabolism; D002852:Chromatography, Ion Exchange; D003001:Cloning, Molecular; D003081:Cold Climate; D005630:Fructans / Q000096:biosynthesis* / Q000737:chemistry; D015723:Gene Library; D006602:Hexosyltransferases / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010843:Pichia / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012621:Seasons; D016415:Sequence Alignment; D012995:Solubility; D014162:Transfection; D014908:Triticum / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics
D005630:Fructans; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D006602:Hexosyltransferases; C097181:sucrose - fructan 6-fructosyltransferase; C114852:1,2-beta-fructan 1(F)-fructosyltransferase