Evolution in the Genus Zea : Lessons from Studies of Nucleotide Polymorphism(Differentiation Patterns of Plant Populations-Modern Approaches and Recent Progress)(INTERNATIONAL SYMPOSIUM : Differentiation Patterns of Plant Populations and Adaptive Mechanis
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概要
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The genus Zea consists of the cultivar maize and six wild taxa. All taxa in the genus hybridize with one another, and the genus appears to be of relatively recent origin. The genus Zea has long been of interest to evolutionary and molecular geneticists, and a plethora of studies have established that maize and the teosintes are genetically diverse. This high diversity, coupled with relatively recent divergence among taxa, makes Zea an excellent model system for studying the distribution of nucleotide diversity both among recently diverged taxa and among a crop and its wild relatives. Nucleotide diversity has been studied in a number of maize loci. These studies have documented tremendous nucleotide variation in maize, and they suggest that allelic lineages in the maize gene pool can be quite long-lived. For example, it has been estimated that allelic lineages have existed for several million years at both the Adh1 and the Adh2 locus, suggesting that the common ancestor to Zea taxa was highly polymorphic. These studies have also found ample evidence of recombination in maize loci, suggesting that recombination plays an important role in generating haplotype diversity. A recent study of the regulatory locus c1, a regulatory gene in the anthocyanin biosynthesis pathway, belies this general picture. Alleles from the c1 locus have been sampled from maize and teosintes. The sampled alleles fall into two discrete groups, corresponding to two distinct functional classes. Both classes are found in teosinte, but only one of these classes is found in maize. The c1 locus is less diverse than any other maize locus yet examined. It is hypothesized that low nucleotide diversity at the c1 locus is a consequence of selection, probably artificial by the early domesticators of maize.
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