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GENETICS, GENOMICS, AND MOLECULAR EVOLUTION

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^1,[W]

National Research Council, Plant Genetics Institute, 130–06128 Perugia, Italy (F.P., L.M., S.A., F.D.); Institute of Grassland and Environmental Research, Aberystwyth, Ceredigion SY23 3EB, United Kingdom (M.P.R.); and Philipps Universität Marburg, Institut für Pharmazeutische Biologie, 35037 Marburg/Lahn, Germany (S.M.)

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.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Francesco Paolocci (francesco.paolocci{at}igv.cnr.it).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.090886

^* Corresponding author; e-mail francesco.paolocci{at}igv.cnr.it; fax 39–075–5014869.

Received October 6, 2006; accepted November 2, 2006; published November 10, 2006.

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