Cloning and functional analysis of a fructosyltransferase cDNA for synthesis of highly polymerized levans in timothy (Phleum pratense L.).
Variation in the structures of plant fructans and their degree of polymerization (DP) can be explained as the result of diverse combinations of fructosyltransferases (FTs) with different properties. Although FT genes have been isolated in a range of plant species, sucrose:fructan 6-fructosyltransferase (6-SFT) cDNAs have only been functionally characterized in a few species such as wheat. A novel FT cDNA possessing 6-SFT activity has been identified and characterized from the temperate forage grass, timothy (Phleum pratense L.). The cDNA of an FT homolog, PpFT1, was isolated from cold-acclimated timothy. A recombinant PpFT1 protein expressed in Pichia pastoris showed 6-SFT/sucrose:sucrose 1-fructosyltransferase (1-SST) activity and produced linear beta(2,6)-linked levans from sucrose with higher DPs than present in graminans formed in vitro by wheat 6-SFT (Wft1). PpFT1 and Wft1 showed remarkably different acceptor substrate specificities: PpFT1 had high affinity for 6-kestotriose to produce levans and low affinity for 1-kestotriose, whereas Wft1 preferentially used 1-kestotriose as an acceptor. The affinity of the PpFT1 recombinant enzyme for sucrose as a substrate was lower than that of the Wft1 recombinant enzyme. It is also confirmed that timothy seedlings had elevated levels of PpFT1 transcripts during the accumulation of fructans under high sucrose and cold conditions. Our results suggest that PpFT1 is a novel cDNA with unique enzymatic properties that differ from those of previously cloned plant 6-SFTs, and is involved in the synthesis of highly polymerized levans in timothy.
Tamura
Ken-ichi
K
National Agricultural Research Center for Hokkaido Region, Hitsujigaoka 1, Toyohira, Sapporo 062-8555, Japan. tamuken@affrc.go.jp
Kawakami
Akira
A
Sanada
Yasuharu
Y
Tase
Kazuhiro
K
Komatsu
Toshinori
T
Yoshida
Midori
M
D000595:Amino Acid Sequence; D050260:Carbohydrate Metabolism; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D003001:Cloning, Molecular; D003080:Cold Temperature; D018076:DNA, Complementary / Q000235:genetics*; D005630:Fructans / Q000096:biosynthesis*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006602:Hexosyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D031784:Phleum / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D016415:Sequence Alignment; D013395:Sucrose / Q000494:pharmacology; D014908:Triticum / Q000187:drug effects / Q000201:enzymology; D001426:Bacterial Proteins
D018076:DNA, Complementary; D005630:Fructans; D006602:Hexosyltransferases; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013395:Sucrose; C097181:sucrose - fructan 6-fructosyltransferase; C021451:inulosucrase; D001426:Bacterial Proteins