The OrcPI locus: genomic organization, expression pattern, and noncoding regions variability in Orchis italica (Orchidaceae) and related species

OrcPI is a class B MADS-box gene of Orchis italica (Orchidaceae), homologous of the PISTILLATA/GLOBOSA gene isolated in Arabidopsis and Antirrhinum. Its role in determining petals and stamens is conserved in orchids, where it seems to be involved also in other functions, such as flower longevity and ovary development. The present study reports the genomic characterization of the OrcPI locus in O. italica including coding and noncoding regions (introns, 5'- and 3' untranslated regions, and putative promoter). Nucleotide polymorphism distribution confirmed that this gene is subjected to different evolutionary forces, phylogenetic and distance analyses demonstrated that OrcPI is a useful nuclear marker at low taxonomic level in orchids. The expression pattern analysis showed that OrcPI transcripts are present in all the floral structures, undetected in the vegetative tissues, and decreased in the natural senescent flower. Finally, micro-RNAs putative target sites were identified within the OrcPI gene, conserved among orchids.