title: The PI/GLO-like locus in orchids: duplication and purifying selection at synonymous sites within Orchidinae (Orchidaceae).
abstract: Positive selection and relaxation of purifying constraints after duplication events have driven the functional diversification of gene families involved in development. One example of this occurred within the plant MADS-box genes. The evolution of the orchid flower was driven by duplication events followed by sub- and neo-functionalization of class B DEF-like MADS-box genes, which are present at three to four copies in the orchid genome. In contrast, the orchid PI/GLO-like class B MADS-box genes have been reported thus far as single-copy loci, with the only exception of Habenaria radiata. We isolated a novel PI/GLO-like gene (OrcPI2) in Orchis italica, which is different than the previously characterized OrcPI locus. The presence of two functional paralogs of PI/GLO-like genes in orchids is detectable only within the tribe Orchidinae. Evolutionary analyses revealed an apparent relaxation of purifying selection acting on the two PI/GLO-like paralogs of the Orchidinae when compared to the single-copy PI/GLO-like genes found in other orchid species. Furthermore, by measuring dN/dS (ω) ratios, we show that a high percentage of sites between the two PI/GLO-like paralogs have different evolutionary pressures. Interestingly, the apparent relaxation of selective constraints on the two PI/GLO-like paralogs is due to strong purifying selection at synonymous sites rather than to a high value of nonsynonymous substitution rate. This peculiar evolutionary pattern might be related to molecular processes such as mRNA folding and/or translational efficiency control. These processes could potentially be involved in or predate the functional diversification of the two PI/GLO-like paralogs within Orchidinae.
authors.affiliation: Department of Biological Sciences, University of Naples Federico II, Via Mezzocannone 8, 80134 Napoli, Italy.
authors.forename: Carmela
authors.initials: C
authors.lastname: Cantone
authors.forename: Luciano
authors.initials: L
authors.lastname: Gaudio
authors.forename: Serena
authors.initials: S
authors.lastname: Aceto
mesh_terms: D000595:Amino Acid Sequence; D019143:Evolution, Molecular; D020440:Gene Duplication; D017343:Genes, Plant; D026161:MADS Domain Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D029595:Orchidaceae / Q000235:genetics*; D010802:Phylogeny; D012641:Selection, Genetic; D016415:Sequence Alignment
chemical_list: D026161:MADS Domain Proteins