New perspectives on proanthocyanidin biochemistry and molecular regulation.
Our understanding of proanthocyanidin (syn. condensed tannin) synthesis has been recently extended by substantial developments concerning both structural and regulatory genes. A gene encoding leucoanthocyanidin reductase has been obtained from the tropical forage, Desmodium uncinatum, with the latter enzyme catalyzing formation of (+)-catechin. The BANYULS gene in Arabidopsis thaliana, previously proposed to encode leucoanthocyanidin reductase or to regulate proanthocyanidin biosynthesis, has been shown instead to encode anthocyanidin reductase, which in turn converts anthocyanidins (pelargonidin, cyanidin, or delphinidin) into 2,3-cis-2R,3R-flavan-3-ols (respectively, (-)-epiafzelechin, (-)-epicatechin and (-)-epigallocatechin). However, the enzyme which catalyzes the polymerization reaction remains unknown. Nevertheless, a vacuolar transmembrane protein TT12, defined by the Arabidopsis tt12 mutant, is involved in transport of proanthocyanidin polymer into the vacuole for accumulation. Six different types of regulatory elements, e.g. TFIIIA-like, WD-40-like, WRKY-like, MADS-box-like, myb-like, and bHLH (myc-like), have been cloned and identified using mutants from Arabidopsis (tt1, ttg1, ttg2, tt2, tt16, tt2, tt8) and two other species (Hordeum vulgare [ant13] and Lotus spp [tan1]). Accordingly, increases in proanthocyanidin levels have been induced in the the world's major forage, alfalfa. These advances may now lead to a detailed understanding of how PA synthesis is controlled and to useful alterations in proanthocyanidin concentration for the improvement of forage species, pulses, and other crop plants.
Marles
M A Susan
MA
Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, Saskatchewan S7N 0X2, Canada.
Ray
Heather
H
Gruber
Margaret Y
MY
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000235:genetics / Q000378:metabolism; D000070116:Lotus / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D044945:Proanthocyanidins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013237:Stereoisomerism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D044945:Proanthocyanidins; D011994:Recombinant Proteins; D014157:Transcription Factors; C013221:proanthocyanidin; D010088:Oxidoreductases