RESUMO
Evolutionary innovations are important drivers of speciation and some are the defining characters of entire phyla. One such major innovation is the carpel, the unifying character and most complex plant organ, composed of many clearly distinct tissue types to ensure reproductive success. The origin of the carpel is unknown, but many components of the gene regulatory network (GRN) governing carpel development and their genetic interactions are known from the core eudicot Arabidopsis thaliana. To unravel the evolution of the carpel GRN and to discriminate between "early" and "late" steps in carpel evolution, we calculated thorough phylogeny reconstructions based on sequenced genomes. The A. thaliana carpel GRN members ALCATRAZ (ALC), CRABS CLAW (CRC), HALF FILLED (HAF), HECATE (HEC), INDEHISCENT (IND), NGATHA (NGA), and SPATULA (SPT) were analyzed in their phylogenetic context. We find that the carpel GRN components are of various ages, but interestingly, we identify especially high retention rates for carpel development genes in Brassicaceae. Our data suggest that genes whose A. thaliana homologs are involved in processes already present in the most recent common ancestor of seed plants, such as reproductive meristem termination or adaxial/abaxial polarity specification, are not retained in duplicates after whole genome duplications (WGD). In contrast, genes involved in processes associated with derived carpel characters in Arabidopsis, such as the transmitting tract or style development show a higher gene retention rate after WGD. This work provides a starting point for analyses of carpel genes in early diverging angiosperms which would be very informative for evolutionary studies.
Assuntos
Arabidopsis/genética , Flores/genética , Sementes/genética , Proteínas de Arabidopsis/genética , Evolução Biológica , Evolução Molecular , Flores/metabolismo , Duplicação Gênica/genética , Regulação da Expressão Gênica no Desenvolvimento/genética , Regulação da Expressão Gênica de Plantas/genética , Genes de Plantas/genética , Magnoliopsida/genética , Meristema/genética , Filogenia , Proteínas de Plantas/genética , Sementes/metabolismoRESUMO
Carpels are the female reproductive organs of flowering plants (angiosperms), enclose the ovules, and develop into fruits. The presence of carpels unites angiosperms, and they are suggested to be the most important autapomorphy of the angiosperms, e.g., they prevent inbreeding and allow efficient seed dispersal. Many transcriptional regulators and coregulators essential for carpel development are encoded by diverse gene families and well characterized in Arabidopsis thaliana. Among these regulators are AGAMOUS (AG), ETTIN (ETT), LEUNIG (LUG), SEUSS (SEU), SHORT INTERNODE/STYLISH (SHI/STY), and SEPALLATA1, 2, 3, 4 (SEP1, 2, 3, 4). However, the timing of the origin and their subsequent molecular evolution of these carpel developmental regulators are largely unknown. Here, we have sampled homologs of these carpel developmental regulators from the sequenced genomes of a wide taxonomic sampling of the land plants, such as Physcomitrella patens, Selaginella moellendorfii, Picea abies, and several angiosperms. Careful phylogenetic analyses were carried out that provide a phylogenetic background for the different gene families and provide minimal estimates for the ages of these developmental regulators. Our analyses and published work show that LUG-, SEU-, and SHI/STY-like genes were already present in the Most Recent Common Ancestor (MRCA) of all land plants, AG- and SEP-like genes were present in the MRCA of seed plants and their origin may coincide with the ξ Whole Genome Duplication. Our work shows that the carpel development regulatory network was, in part, recruited from preexisting network components that were present in the MRCA of angiosperms and modified to regulate gynoecium development.
