Plant Physiology, Vol. 127, pp. 46-57
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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 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 onditions assayed. The
expression of the maize A1 gene in the flavonoid 3'
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.
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