Expression pattern of two paralogs of the PI/GLO-like locus during Orchis italica (Orchidaceae, Orchidinae) flower development

Abstract

The class B MADS-box genes belong to two distinct functional groups: the AP3/DEF-like and the PI/GLO-like sub-families. In orchids, AP3/DEF-like genes are present in four copies, each with a different role in floral organ formation, which is described in the "orchid code" model. Interestingly, the orchid PI/GLO-like genes are present in two copies in Orchidinae, whereas they are described as single copy in the other orchid lineages. The two PI/GLO-like paralogs have site-specific different selective constraints; in addition, they show relaxation of purifying selection when compared to the single-copy lineages. In this study, we present a comparative analysis of the expression patterns of the two PI/GLO-like paralogs, OrcPI and OrcPI2, in floral tissues of Orchis italica in different developmental stages using real-time PCR. The two genes show similar expression profiles in the tissue examined, with differences detectable between immature and mature inflorescence. In all cases, OrcPI2 is expressed at a higher level than OrcPI. Real-time PCR results reveal that the co-expression of the two duplicated loci could have a fully or partially redundant function. The possible evolutionary fate of OrcPI and OrcPI2 is discussed as well as their involvement in ovary development.

The Analysis of the Inflorescence miRNome of the Orchid Orchis italica Reveals a DEF-Like MADS-Box Gene as a New miRNA Target

“…The actin OitaAct gene was used as endogenous control [GenBank: AB630020]. Amplification conditions are reported elsewhere [16]. The amplification data were processed as described above.…”

“…All the genes involved in the (A)BCDE model, except the class A gene APETALA2 ( AP2 ), are MADS-box transcriptional factors. Although this model is applicable to most flowering plants, in orchids it shows modifications in the expression domains of the class B GLOBOSA -like ( GLO -like) and DEFICIENS -like ( DEF -like) genes [15], [16], [17], [18] and of the class C ( AGAMOUS -like) and D ( SEEDSTICK -like) genes [19], [20]. To date, the only gene belonging to the (A)BCDE model and negatively regulated by a miRNA is AP2 , whose transcript is cleaved by miR172 with a conserved mechanism present also in orchids [10], [21].…”

Promotion of Efficient Molecular Breeding Using Chimeric Repressors in Ornamental Flowers

“…For example, the mutant phenotype of Arabidopsis TCP was not sufficiently observed even in a triple mutant (Koyama et al 2010). Class B MADS-box genes that play important roles in the formation of petals and stamens are redundantly found in such horticultural crops as Gerbera hybrida (Broholm et al 2010), Orchis italica (Salemme et al 2011), and Petunia hybrida (Vandenbussche et al 2004), but not in Arabidopsis and A. majus. The analysis of such redundant TFs by a single mutation has limitations, particularly in higher polyploidy plants.…”

De novo sequencing and comparative transcriptome analysis of white petals and red labella in Phalaenopsis for discovery of genes related to flower color and floral differentation

“…Floral initiation and development are regulated by complex networks of exogenous and endogenous signals, including light stimuli, hormones, ligand-receptor interactions, signal transduction pathways, and transcription factor cascades [4]. A recent theory known as "the orchid code" proposes a reasonable model in which four different class B AP3/DEF-like MADSbox genes have played a vital role in the evolution of the orchid perianth by their combinatorial interaction.…”

“…Differential expression of clade 3 genes is obviously responsible for differences between inner and outer tepals, whereas differential expression of clade 4 genes differentiates the lateral inner tepals from the labella [2,3]. Orchid PI/GLO-like genes, found to be present in the AP3/ DEF-like gene copies, are also necessary for current floral tissue development [4]. Despite this knowledge, however, the regulatory network controlling orchid floral development remains unclear.…”