Molecular evolution of the OrcPI locus in natural populations of Mediterranean orchids.

The evolutionary analysis of OrcPI, the orchid homologue to the PISTILLATA/GLOBOSA gene, was conducted on some Mediterranean orchid species, measuring mean pairwise Ka/Ks ratios and nucleotide variability. Evidence for positive selection was tested using a maximum likelihood approach implemented in PAML, and neutrality tests were conducted to assess deviation from neutral evolution. Data were also examined partitioning the coding region into four regions, corresponding to different functional domains of the protein. The results show that OrcPI is subjected to different evolutionary forces: diffuse purifying selection, localized positive selection or selective sweep, and different partitions of selective constraints.