B-class gene GLOBOSA - a facilitator for enriched species diversity of Salvia in the New World?

The genus Salvia, comprising around 1000 species, half of which are found in the New World, belongs to the taxonomically most challenging genera within the Lamiaceae. A part of this diversity can be ascribed to the shape and expansion of the corolla and stamen structures, because changes in geometry of the sexual organs and attractance of pollinators might establish propagation barriers. However, the structural, functional, and evolutionary context of the underlying genes has not yet been elaborated. In this study, we analyse a large set of flowers from Salvia species of different geographic origin and use this morphometric framework to address gene expression and phylogenetic analysis of the MADS-box B-class gene, GLOBOSA. We examined expression of GLOBOSA in petals and anthers throughout anthesis for both Salvia pratensis L., as species from Europe, and the American Salvia elegans Vahl. Structural analysis of the B-class genes reveals typical MADS-MIKC-type composition. When we infer phylogenies for GLOBOSA and its binding partner DEFICIENS, we see a genus-wide duplication of DEFICIENS in Salvia and a specific duplication of GLOBOSA in Salvia species from the New World. Based on the first description of flowering genes in the genus Salvia, we arrive at a working model, where a duplication of GLOBOSA enabled the intense radiation of New World Salvia by neo-functionalization of a flower identity gene for morphogenetic control of corolla and anther geometry. We propose that the genus Salvia can be used as paradigm to address the role of EvoDevo for plant speciation.