title: Ectopic expression of a basic helix-loop-helix gene transactivates parallel pathways of proanthocyanidin biosynthesis. structure, expression analysis, and genetic control of leucoanthocyanidin 4-reductase and anthocyanidin reductase genes in Lotus corniculatus.
abstract: Proanthocyanidins (PAs) are plant secondary metabolites and are composed primarily of catechin and epicatechin units in higher plant species. Due to the ability of PAs to bind reversibly with plant proteins to improve digestion and reduce bloat, engineering this pathway in leaves is a major goal for forage breeders. Here, we report the cloning and expression analysis of anthocyanidin reductase (ANR) and leucoanthocyanidin 4-reductase (LAR), two genes encoding enzymes committed to epicatechin and catechin biosynthesis, respectively, in Lotus corniculatus. We show the presence of two LAR gene families (LAR1 and LAR2) and that the steady-state levels of ANR and LAR1 genes correlate with the levels of PAs in leaves of wild-type and transgenic plants. Interestingly, ANR and LAR1, but not LAR2, genes produced active proteins following heterologous expression in Escherichia coli and are affected by the same basic helix-loop-helix transcription factor that promotes PA accumulation in cells of palisade and spongy mesophyll. This study provides direct evidence that the same subclass of transcription factors can mediate the expression of the structural genes of both branches of PA biosynthesis.
authors.affiliation: National Research Council, Plant Genetics Institute, 130-06128 Perugia, Italy. francesco.paolocci@igv.cnr.it
authors.forename: Francesco
authors.initials: F
authors.lastname: Paolocci
authors.forename: Mark P
authors.initials: MP
authors.lastname: Robbins
authors.forename: Laura
authors.initials: L
authors.lastname: Madeo
authors.forename: Sergio
authors.initials: S
authors.lastname: Arcioni
authors.forename: Stefan
authors.initials: S
authors.lastname: Martens
authors.forename: Francesco
authors.initials: F
authors.lastname: Damiani
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015139:Blotting, Southern; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry; D018506:Gene Expression Regulation, Plant; D000070116:Lotus / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000201:enzymology; D044945:Proanthocyanidins / Q000032:analysis / Q000096:biosynthesis* / Q000737:chemistry; D015398:Signal Transduction; D015533:Transcriptional Activation
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018076:DNA, Complementary; D010088:Oxidoreductases; D010940:Plant Proteins; D044945:Proanthocyanidins; C013221:proanthocyanidin