The molecular evolution of the Opaque-2 (O2) locus within members of the grass family was analyzed. Eleven accessions covering all Zea taxa and one Tripsacum dactyloides accession were assayed, identifying 21 haplotypes. O2 appears highly polymorphic, with estimates of nucleotide diversity being among the highest reported for maize and with synonymous site substitution rates (2.2 - 3.6 × 10 -8 substitutions/site/year) close to the upper limit of estimated substitution rates for plant nuclear loci. The pattern of silent site variation encountered does not predict a strong influence of natural selection. Conversely, nonsynonymous polymorphic sites occur at low frequency in the exons encoding the active domain, revealing strong selective pressure. Recombination events have frequently occurred among the accessions analyzed, reducing the power of phylogenetic analysis. Still, limited grouping of Zea taxa was achieved and confirmed by Mantel tests. The estimated effective population size of Zea (3.9-6.4 × 10 5), based on O2 synonymous site polymorphism, appears in good agreement with previous estimates based on synonymous polymorphism. Finally, analysis of evolutionary rates indicates that all species belonging to the Zea phylum as well as T. dactyloides have evolved at an identical pace.
Molecular evolution of Opaque-2, a regulatory locus in the genus Zea
Pirona, R;
2002
Abstract
The molecular evolution of the Opaque-2 (O2) locus within members of the grass family was analyzed. Eleven accessions covering all Zea taxa and one Tripsacum dactyloides accession were assayed, identifying 21 haplotypes. O2 appears highly polymorphic, with estimates of nucleotide diversity being among the highest reported for maize and with synonymous site substitution rates (2.2 - 3.6 × 10 -8 substitutions/site/year) close to the upper limit of estimated substitution rates for plant nuclear loci. The pattern of silent site variation encountered does not predict a strong influence of natural selection. Conversely, nonsynonymous polymorphic sites occur at low frequency in the exons encoding the active domain, revealing strong selective pressure. Recombination events have frequently occurred among the accessions analyzed, reducing the power of phylogenetic analysis. Still, limited grouping of Zea taxa was achieved and confirmed by Mantel tests. The estimated effective population size of Zea (3.9-6.4 × 10 5), based on O2 synonymous site polymorphism, appears in good agreement with previous estimates based on synonymous polymorphism. Finally, analysis of evolutionary rates indicates that all species belonging to the Zea phylum as well as T. dactyloides have evolved at an identical pace.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
