RESUMEN
Certain regions on the surfaces of developing pollen grains exhibit very limited deposition of pollen wall exine. These regions give rise to pollen apertures, which are highly diverse in their patterns and specific for individual species. Arabidopsis thaliana pollen develops three equidistant longitudinal apertures. The precision of aperture formation suggests that, to create them, pollen employs robust mechanisms that generate distinct cellular domains. To identify players involved in this mechanism, we screened natural Arabidopsis accessions and discovered one accession, Martuba, whose apertures form abnormally due to the disruption of the protein kinase D6PKL3. During pollen development, D6PKL3 accumulates at the three plasma membrane domains underlying future aperture sites. Both D6PKL3 localization and aperture formation require kinase activity. Proper D6PKL3 localization is also dependent on a polybasic motif for phosphoinositide interactions, and we identified two phosphoinositides that are specifically enriched at the future aperture sites. The other known aperture factor, INAPERTURATE POLLEN1, fails to aggregate at the aperture sites in d6pkl3 mutants, changes its localization when D6PKL3 is mislocalized, and, in turn, affects D6PKL3 localization. The discovery of aperture factors provides important insights into the mechanisms cells utilize to generate distinct membrane domains, develop cell polarity, and pattern their surfaces.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Membrana Celular/metabolismo , Polen/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Membrana Celular/genética , Mutación , Polen/genéticaRESUMEN
Natural epigenetic variation provides a source for the generation of phenotypic diversity, but to understand its contribution to such diversity, its interaction with genetic variation requires further investigation. Here we report population-wide DNA sequencing of genomes, transcriptomes and methylomes of wild Arabidopsis thaliana accessions. Single cytosine methylation polymorphisms are not linked to genotype. However, the rate of linkage disequilibrium decay amongst differentially methylated regions targeted by RNA-directed DNA methylation is similar to the rate for single nucleotide polymorphisms. Association analyses of these RNA-directed DNA methylation regions with genetic variants identified thousands of methylation quantitative trait loci, which revealed the population estimate of genetically dependent methylation variation. Analysis of invariably methylated transposons and genes across this population indicates that loci targeted by RNA-directed DNA methylation are epigenetically activated in pollen and seeds, which facilitates proper development of these structures.
Asunto(s)
Arabidopsis/genética , Epigénesis Genética/genética , Variación Genética/genética , Genoma de Planta/genética , Metilación de ADN/genética , Elementos Transponibles de ADN/genética , Epigenómica , Desequilibrio de Ligamiento/genética , Polen/genética , Polimorfismo Genético/genética , Sitios de Carácter Cuantitativo , ARN Mensajero/análisis , ARN Mensajero/genética , ARN de Planta/genética , Semillas/genéticaRESUMEN
In many plant species, exposure to a prolonged period of cold during the winter promotes flowering in the spring, a process termed vernalization. In Arabidopsis thaliana, the vernalization requirement of winter-annual ecotypes is caused by the MADS-box gene FLOWERING LOCUS C (FLC), which is a repressor of flowering. During the vernalization process, FLC is downregulated by alteration of its chromatin structure, thereby permitting flowering to occur. In wheat, a vernalization requirement is imposed by a different repressor of flowering, suggesting that some components of the regulatory network controlling the vernalization response differ between monocots and dicots. The extent to which the molecular mechanisms underlying vernalization have been conserved during the diversification of the angiosperms is not well understood. Using phylogenetic analysis, we identified homologs of FLC in species representing the three major eudicot lineages. FLC homologs have not previously been documented outside the plant family Brassicaceae. We show that the sugar beet FLC homolog BvFL1 functions as a repressor of flowering in transgenic Arabidopsis and is downregulated in response to cold in sugar beet. Cold-induced downregulation of an FLC-like floral repressor may be a central feature of the vernalization response in at least half of eudicot species.