Functional Conservation of Plant Secondary Metabolic Enzymes Revealed by Complementation of Arabidopsis Flavonoid Mutants with Maize Genes

Abstract

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 form a 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 conditions assayed. The expression of the maize A1 gene in the flavonoid 3Ј hydroxylase Arabidopsis tt7 mutant 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.

A Trafficking Pathway for Anthocyanins Overlaps with the Endoplasmic Reticulum-to-Vacuole Protein-Sorting Route in Arabidopsis and Contributes to the Formation of Vacuolar Inclusions

“…As previously described (Dong et al, 2001), a single spot corresponding to cyanidin was observed, which was absent in tt5 seedlings (Supplemental Fig. S1A).…”

A Stilbene Synthase Gene (SbSTS1) Is Involved in Host and Nonhost Defense Responses in Sorghum

“…4A), indicating the accumulation of tannins in seed coats. In addition, these transgenic seedlings showed anthocyanin pigments in cotyledons and hypocotyls when germinated in medium devoid of nitrogen sources, a sensitive condition previously employed to induce the anthocyanin biosynthesis pathway in Arabidopsis (Hsieh et al, 1998;Dong et al, 2001). In contrast, seed coats of SbCHS8-expressing tt4 plants remained yellow in both T 1 and T 2 generations and the transgenic seedlings failed to accumulate anthocyanin under nitrogen deficiency (Fig.…”

“…The complementation of Arabidopsis transparent testa (tt) mutants by maize genes demonstrated the convenience of this system for establishing the function of uncharacterized coding sequences with homology to flavonoid structural genes (Dong et al, 2001). Arabidopsis tt4 mutants are deficient in CHS activities, resulting in the absence of flavonoid-derived metabolites in different tissues.…”

Flavonoid Phytoalexin-Dependent Resistance to Anthracnose Leaf Blight Requires a Functional yellow seed1 in Sorghum bicolor

“…The activation of biosynthetic genes in metabolic pathways is often coordinated by transcription factors. Chalcone synthase (CHS) and chalcone isomerase (CHI) are two early pathway enzymes that drive the flavonoid pathway toward the formation of naringenin, the common precursor of many flavonoid compounds including anthocyanins, flavones, and phlobaphenes (Dong et al 2001;Winkel-Shirley 2001a,b). Gene expression analysis in the y1 mutant and wild-type genotypes further revealed that the transcription of these biosynthetic genes is y1 dependent.…”