RESUMO
Timing of flowering is key to the reproductive success of many plants. In temperate climates, flowering is often coordinated with seasonal environmental cues such as temperature and photoperiod. Vernalization, the process by which a prolonged exposure to the cold of winter results in competence to flower during the following spring, is an example of the influence of temperature on the timing of flowering. In different groups of plants, there are distinct genes involved in vernalization, indicating that vernalization systems evolved independently in different plant groups. The convergent evolution of vernalization systems is not surprising given that angiosperm families had begun to diverge in warmer paleoclimates in which a vernalization response was not advantageous. Here, we review what is known of the vernalization response in three different plant groups: crucifers (Arabidopsis), Amaranthaceae (sugar beet), and Pooideae (wheat, barley, and Brachypodium distachyon). We also discuss the advantages of using Brachypodium as a model system to study flowering and vernalization in the Pooids. Finally, we discuss the evolution and function of the Ghd7/VRN2 gene family in grasses.
Assuntos
Temperatura Baixa , Flores/genética , Flores/fisiologia , Plantas/genética , Arabidopsis/genética , Arabidopsis/fisiologia , Beta vulgaris/genética , Beta vulgaris/fisiologia , Brachypodium/genética , Brachypodium/fisiologia , Hordeum/genética , Hordeum/fisiologia , Fotoperíodo , Filogenia , Proteínas de Plantas/metabolismo , Transdução de Sinais/genética , Triticum/genética , Triticum/fisiologiaRESUMO
Eukaryotes have three multisubunit DNA-dependent RNA polymerases that are essential for viability, abbreviated as Pol I, Pol II, and Pol III. Remarkably, Arabidopsis thaliana and other higher plants contain two additional nuclear multisubunit RNA polymerases, Pol IV and Pol V. These plant-specific polymerases are not essential for viability but have nonredundant roles in RNA-mediated gene-silencing pathways. Proteomic analyses have revealed that Arabidopsis Pol IV and Pol V have a 12-subunit composition like Pol II. In fact, half of the subunits of Pols II, IV, and V are encoded by the same genes. The remaining Pol IV- or Pol V-specific subunit genes arose through duplication and subfunctionalization of ancestral Pol II subunit genes. These include the genes encoding the largest subunits unique to Pol IV or Pol V, the genes encoding the second- and the fourth-largest subunits that are used by both Pol IV and Pol V, the gene encoding the fifth-largest subunit unique to Pol V and the genes encoding the seventh-largest subunits that are unique to Pol IV and Pol V. On the basis of phylogenetic reconstructions, the gene duplication events giving rise to the first-, second-, fourth-, fifth-, and seventh-largest subunits of Pol IV and/or Pol V occurred independently. Interestingly, a cDNA-mediated duplication of the Pol II seventh-largest subunit gene via retro-tranposition was an early event in Pol IV evolution, preceded only by the duplications of the largest and second-largest subunit genes. Secondary duplication of this cDNA-like gene to generate Pol IV- and Pol V-specific seventh-largest subunits has occurred in Arabidopsis but not all dicotyledonous plants or monocots, indicative of the dynamic evolution of RNA Pol IV and Pol V in plants.
Assuntos
RNA Polimerases Dirigidas por DNA/genética , Evolução Molecular , Duplicação Gênica/genética , Genoma de Planta/genética , Filogenia , Retroelementos/genética , Duplicações Segmentares Genômicas/genética , Sequência de Aminoácidos , Animais , Sequência Conservada/genética , RNA Polimerases Dirigidas por DNA/metabolismo , Genes de Plantas/genética , Humanos , Íntrons/genética , Medicago truncatula/enzimologia , Medicago truncatula/genética , Família Multigênica/genética , Subunidades Proteicas/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismoRESUMO
We conducted a test to detect if there is a heritable epigenetic component to hybrid vigor and/or inbreeding depression. The impetus for this work was a classical study of the effect of homozygosis on the expression of the maize red color ( r1) locus. It had been shown that maintaining R1 mottling alleles in the homozygous state over several generations produces a progressive decrease of their paternally imprinted expression. This effect is reversed by R1/r1 allele heterozygosity. If this behavior were characteristic of many regulatory genes, then such a phenomenon could contribute to inbreeding depression and heterosis. To examine this question, inbreds of Mo17 and B73 and the two reciprocally produced hybrids were crossed by Stock 6 to generate four classes of maternal haploids. The mature haploid plants were measured for several quantitative traits. If inbreeding depression results from an accumulating heritable effect that is reversed by the hybrid state, one would expect the haploids derived from the hybrids to perform better than those derived from the inbred lines. The hybrid-derived haploids did not exhibit greater average performance than the inbred-derived haploids. These data fail to support the hypothesis that inbreeding depression and heterosis have a metastable epigenetic component.
