Transcriptome-wide identification and expression analysis of DIVARICATA-and RADIALIS-like genes of the mediterranean orchid Orchis Italica

Abstract

Bilateral symmetry of flowers is a relevant novelty that has occurred many times throughout the evolution of flowering plants. In Antirrhinum majus, establishment of flower dorso-ventral asymmetry ismainly due to interaction of TCP (CYC and DICH) andMYB (DIV, RAD, and DRIF) transcription factors. In the present study, we characterized 8 DIV-, 4 RAD-, and 2 DRIF-like genes from the transcriptome of Orchis italica, an orchid species with bilaterally symmetric and resupinate flowers. We found a similar number of DIV- andRAD-like geneswithin the genomes of Phalaenopsis equestris and Dendrobium catenatum orchids. Orchid DIV- and RADlike proteins share conservedmotifswhose distribution reflects their phylogeny and analysis of the genomic organization revealed a single intron containing many traces of transposable elements. Evolutionary analysis has shown that purifying selection acts on the DIV- andRAD-like coding regions in orchids, with relaxation of selective constraints in a branch of the DIV-like genes. Analysis of the expression patterns of DIV-and RAD-likegenes in O. italica revealed possible redundant functions for someof them.In theperianthof O. italica, the ortholog of DIV and DRIF of A. majus are expressed in all tissues, whereas RAD ismainly expressed intheouter tepals and lip. These data allowfor proposal of an evolutionary conservedmodel inwhich the expression of the orthologs of the DIV, RAD, and DRIF genes might be related to establishment of flower bilateral symmetry in the nonmodel orchid species O. italica.