Plant Physiology, Vol. 127, pp. 46-57
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Functional Conservation of Plant Secondary Metabolic Enzymes Revealed by Complementation of Arabidopsis Flavonoid Mutants with Maize Genes
Xiaoyun Dong,
Department of Plant Biology and Plant Biotechnology Center, Ohio State University, Columbus, Ohio 43210 (all authors);
E.L.B. is currently in the Department of Zoology at the University of Florida.
Mutations in the transparent testa (tt) loci abolish pigment production in Arabidopsis seed coats. The TT4, TT5, and TT3 loci encode chalcone synthase, chalcone isomerase, and dihydroflavonol 4-reductase, respectively, which are essential for anthocyanin accumulation and may forma macromolecular complex. Here, we show that the products of the maize (Zea mays) C2, CHI1, and A1 genes complement Arabidopsis tt4, tt5, and tt3 mutants, restoring the ability of these mutants to accumulate pigments in seed coats and seedlings. Overexpression of the maize genes in wild-type Arabidopsis seedlings does not result in increased anthocyanin accumulation, suggesting that the steps catalyzed by these enzymes are not rate limiting in the onditions assayed. The expression of the maize A1 gene in the flavonoid 3′ hydroxylase Arabidopsis tt7mutant resulted in an increased accumulation of pelargonidin. We conclude that enzymes involved in secondary metabolism can be functionally exchangeable between plants separated by large evolutionary distances. This is in sharp contrast to the notion that the more relaxed selective constrains to which secondary metabolic pathways are subjected is responsible for the rapid divergence of the corresponding enzymes.
This work was supported in part by the National Science Foundation (grant nos. MCB-9974474 and MCB-9896111 to E.G.) and by the U.S. Department of Agriculture (postdoctoral fellowship no. USDA 1999-01582 to E.L.B.).
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