Allopolyploidization and evolution of species with reduced floral structures inLepidiumL. (Brassicaceae)

Abstract

Understanding the pattern of speciation in a group of plants is critical for understanding its morphological evolution. Lepidium is the genus with the largest variation in floral structure in Brassicaceae, a family in which the floral ground plan is remarkably stable. However, flowers in more than half of Lepidium species have reduced stamen numbers, and most of these also have reduced petals. The species with reduced flowers are geographically biased, distributed mostly in the Americas and Australia͞ New Zealand. Previous phylogenetic studies using noncoding regions of chloroplast DNA and rDNA internal transcribed spacer were incongruent in most New World species relationships. These data, combined with the presence of many polyploid Lepidium species, implied a reticulate history of the genus but did not provide enough information to infer the evolutionary pattern of flower structures. To address this question more thoroughly, sequences of the first intron of a single copy nuclear gene, PISTILLATA, were determined from 43 species. Phylogenetic analysis of the PI intron suggests that many species in the New World have originated from allopolyploidization, and that this is correlated with floral reduction. Interspecific hybrids were generated to understand why allopolyploidization is associated with reduced flowers. The phenotypes of F1 flowers indicate allelic dominance of the absence of lateral stamens, suggesting that propagation of dominant alleles through interspecific hybridization could account for the abundance of the allopolyploid species without lateral stamens.T hrough the study of model plant species, it is relatively well understood how organ identity is regulated in flowers (1-3). However, the underlying genetic mechanisms that lead to the remarkable variation in flower structures in angiosperms are not known. One way to address this question is to analyze floral variation in closely related species. Knowledge of the genetic bases of phenotypic variation between related species for which we know the phylogeny should lead to an understanding of the number of genetic changes underlying phenotypic evolution and other events that lead to the dispersal of certain phenotype(s).The basic floral ground plan of Brassicaceae is well conserved, with four sepals, four petals, six stamens, and two carpels (Fig. 1A). However, within Lepidium L. (Ϸ175 species worldwide), more than half of the species have only two or four stamens (Fig.

Spatiotemporal Seed Development Analysis Provides Insight into Primary Dormancy Induction and Evolution of theLepidium DELAY OF GERMINATION1Genes

“…Comparative work with Lepidium spp. and Arabidopsis seeds (Linkies et al, 2009;Graeber et al, 2010Graeber et al, , 2011Voegele et al, 2011), fruits Mühlhausen et al, 2010), and flowers (Lee et al, 2002) emphasizes that the genus Lepidium provides a phylogenetically and environmentally defined framework highly suited for evolutionary and developmental research on seed/ fruit-related traits. DOG1 gene homologs are present in Lepidium spp.…”

“…The abundant presence of polyploid Lepidium spp. in Australia implied a reticulate history of the genus on this continent characterized by hybridization/ polyploidization events (Lee et al, 2002;Mummenhoff et al, 2004;Dierschke et al, 2009). Lepidium oxytrichum and L. papillosum differ only in trichome type.…”

Systematics and phylogeny of the Brassicaceae (Cruciferae): an overview

“…More problematic is the delimitation of taxa the evolutionary history of which involved extensive polyploidy, hybridization, and apomixis. Polyploidy and hybridization have been well documented in Draba (Brochmann 1992;Brochmann et al 1992 and references therein; Widmer and Baltisberger 1999a, b;Koch and Al-Shehbaz 2002;Scheen et al 2002;Beilstein and Windham 2003;Grundt et al 2004), Cardamine (Neuffer and Janche 1997;Urbanska et al 1997;Franzke et al 1998;Franzke and Mummenhoff 1999;Franzke and Hurka 2000;Lihova´et al 2000;Bleeker et al 2002a;Marhold et al 2002aMarhold et al , 2002bMarhold et al , 2004, and Lepidium (Lee et al 2002;Mummenhoff et al 2001a, 2004 andreferences therein). It is likely that these two phenomena influenced the evolution of all major genera of the family.…”

Allopolyploid speciation inPersicaria(Polygonaceae): Insights from a low-copy nuclear region

“…However, the often relatively low variation in cpDNA at the intraspecific level, and the susceptibility of the commonly used nuclear ribosomal internal transcribed spacer (nrITS) region to concerted evolution (12,13), have limited the precision with which allopolyploidy can be identified. In contrast, the use of low-copy nuclear genes can provide more information when particular gene copies in allopolyploids can be linked with genes in the maternal and paternal lineages (14)(15)(16)(17)(18). Despite technical difficulties in identifying appropriate markers and in comparing proper orthologs, several useful nuclear genes have been tested in studies of allopolyploidy (16).…”