Proanthocyanidin biosynthesis in plants. Purification of legume leucoanthocyanidin reductase and molecular cloning of its cDNA.
Leucoanthocyanidin reductase (LAR) catalyzes the synthesis of catechin, an initiating monomer of condensed tannin or proanthocyanidin (PA) synthesis, from 3,4-cis-leucocyanidin and thus is the first committed step in PA biosynthesis. The enzyme was purified to near homogeneity from PA-rich leaves of the legume Desmodium uncinatum (Jacq.) DC, partially sequenced and the corresponding cDNA cloned. The identity of the enzyme was confirmed by expressing active recombinant LAR in Escherichia coli and in tobacco and white clover. The enzyme is a monomer of 43 kDa (382 amino acids) and is most active synthesizing catechin (specific activity of approximately 10 micromol min+1 mg of protein+1) but also synthesizes afzelechin and gallocatechin. LAR is most closely related to the isoflavone reductase group of plant enzymes that are part of the Reductase-Epimerase-Dehydrogenase (RED) family of proteins. Unlike all other plant isoflavone reductase homologues that are about 320 amino acids long, LAR has an additional 65-amino acid C-terminal extension whose function is not known. Curiously, although Arabidopsis makes PA, there is no obvious LAR orthologue in the Arabidopsis genome. This may be because Arabidopsis seems to produce only an epicatechin, rather than a dual catechin/epicatechin-based PA similar to many other plants.
Tanner
Gregory J
GJ
CSIRO Plant Industry, GPO Box 1600, Canberra, Australian Capital Territory 2601, Australia. greg.tanner@csiro.au
Francki
Kathy T
KT
Abrahams
Sharon
S
Watson
John M
JM
Larkin
Philip J
PJ
Ashton
Anthony R
AR
D000595:Amino Acid Sequence; D000872:Anthocyanins / Q000096:biosynthesis*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D007887:Fabaceae / Q000201:enzymology / Q000378:metabolism*; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D044945:Proanthocyanidins; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D000872:Anthocyanins; D018076:DNA, Complementary; D044945:Proanthocyanidins; D011994:Recombinant Proteins; C013221:proanthocyanidin; D010088:Oxidoreductases