ABSTRACT: Reciprocal crosses of a diploid Arabidopsis with different ploidies results in different endosperm development patterns and phenotype. Typically if the ploidy is higher on the maternal side, there are fewer endosperm cells which cellularize early, and conversely, if the paternal ploidy is higher, there is more number of endosperm cells which cellularize late. Crosses involving diploid and tetraploid Arabidopsis (C24) are viable, whereas crosses involving the diploid and hexaploid, even though exhibit the above mentioned directional trend in endosperm development, abort (Scott et al 1998). The 'maternalised' and 'paternalised' development of endosperm is also observed in crosses involving some Arabidopsis mutants. Mutants in the fis class of genes, e.g. fis1-medea, when crossed with a diploid Arabidopsis (pollen parent) show endosperm development-seed development similar to a diploid (seed parent) crossed with hexaploid pollen parent. Reciprocal crosses of homozygous met1 and diploid Arabidopsis also exhibit reciprocal trends in endosperm development, where a homozygous met1 mutant (seed parent) crossed with diploid is similar in phenotype to a diploid (seed parent) - tetraploid cross. Endosperm development in the reciprocal cross has phenotypic similarity to the tetraploid (seed parent)-diploid cross (Adams et al 2000). We are interested in understanding gene profiles and trends in expression underlying the endosperm development in the interploidy crosses as well as the fis and met1 mutant. 11 samples were used in this experiment.
Project description:Reciprocal crosses of a diploid Arabidopsis with different ploidies results in different endosperm development patterns and phenotype. Typically if the ploidy is higher on the maternal side, there are fewer endosperm cells which cellularize early, and conversely, if the paternal ploidy is higher, there is more number of endosperm cells which cellularize late. Crosses involving diploid and tetraploid Arabidopsis (C24) are viable, whereas crosses involving the diploid and hexaploid, even though exhibit the above mentioned directional trend in endosperm development, abort (Scott et al 1998). The 'maternalised' and 'paternalised' development of endosperm is also observed in crosses involving some Arabidopsis mutants. Mutants in the fis class of genes, e.g. fis1-medea, when crossed with a diploid Arabidopsis (pollen parent) show endosperm development-seed development similar to a diploid (seed parent) crossed with hexaploid pollen parent. Reciprocal crosses of homozygous met1 and diploid Arabidopsis also exhibit reciprocal trends in endosperm development, where a homozygous met1 mutant (seed parent) crossed with diploid is similar in phenotype to a diploid (seed parent) - tetraploid cross. Endosperm development in the reciprocal cross has phenotypic similarity to the tetraploid (seed parent)-diploid cross (Adams et al 2000). We are interested in understanding gene profiles and trends in expression underlying the endosperm development in the interploidy crosses as well as the fis and met1 mutant.
Project description:Seed development is sensitive to parental dosage, with excess maternal or paternal genomes creating reciprocal phenotypes. Paternal genomic excess results in extensive endosperm proliferation without cellularization and eventual seed abortion. We previously showed that loss of the RNA POL IV gene nrpd1 in tetraploid fathers represses seed abortion in paternal excess crosses. Here we show genetically that RNA-directed DNA methylation (RdDM) pathway activity in the paternal parent is sufficient to determine the viability of paternal excess seeds. The status of the RdDM pathway in paternal excess endosperm does not impact seed viability. Comparison of endosperm transcriptomes, DNA methylation, and small RNAs from balanced and paternal excess endosperm demonstrates that paternal excess seed abortion is unlikely to be dependent on either transposable element or imprinted gene mis-regulation. We suggest instead that loss of paternal RdDM modulates expression at a small subset of genes and desensitizes endosperm to paternal excess. Finally, using allele-specific transcription data, we present evidence of a transcriptional buffering system that up37 regulates maternal alleles and represses paternal alleles in response to excess paternal genomic dosage. These findings prompt reconsideration of models for dosage sensitivity in endosperm.
Project description:Seed development is sensitive to parental dosage, with excess maternal or paternal genomes creating reciprocal phenotypes. Paternal genomic excess results in extensive endosperm proliferation without cellularization and eventual seed abortion. We previously showed that loss of the RNA POL IV gene nrpd1 in tetraploid fathers represses seed abortion in paternal excess crosses. Here we show genetically that RNA-directed DNA methylation (RdDM) pathway activity in the paternal parent is sufficient to determine the viability of paternal excess seeds. The status of the RdDM pathway in paternal excess endosperm does not impact seed viability. Comparison of endosperm transcriptomes, DNA methylation, and small RNAs from balanced and paternal excess endosperm demonstrates that paternal excess seed abortion is unlikely to be dependent on either transposable element or imprinted gene mis-regulation. We suggest instead that loss of paternal RdDM modulates expression at a small subset of genes and desensitizes endosperm to paternal excess. Finally, using allele-specific transcription data, we present evidence of a transcriptional buffering system that up37 regulates maternal alleles and represses paternal alleles in response to excess paternal genomic dosage. These findings prompt reconsideration of models for dosage sensitivity in endosperm.
Project description:Seed development is sensitive to parental dosage, with excess maternal or paternal genomes creating reciprocal phenotypes. Paternal genomic excess results in extensive endosperm proliferation without cellularization and eventual seed abortion. We previously showed that loss of the RNA POL IV gene nrpd1 in tetraploid fathers represses seed abortion in paternal excess crosses. Here we show genetically that RNA-directed DNA methylation (RdDM) pathway activity in the paternal parent is sufficient to determine the viability of paternal excess seeds. The status of the RdDM pathway in paternal excess endosperm does not impact seed viability. Comparison of endosperm transcriptomes, DNA methylation, and small RNAs from balanced and paternal excess endosperm demonstrates that paternal excess seed abortion is unlikely to be dependent on either transposable element or imprinted gene mis-regulation. We suggest instead that loss of paternal RdDM modulates expression at a small subset of genes and desensitizes endosperm to paternal excess. Finally, using allele-specific transcription data, we present evidence of a transcriptional buffering system that up37 regulates maternal alleles and represses paternal alleles in response to excess paternal genomic dosage. These findings prompt reconsideration of models for dosage sensitivity in endosperm.
Project description:To investigate genome-wide maternal and paternal contributions to polyploid grain development, we produced and analyzed transcriptomes from zygote to mature stage embryos as well as two endosperm stages derived from reciprocal crosses between tetraploid and hexaploid wheats.
Project description:In Arabidopsis seed development involves maternal small interfering RNAs (siRNAs) that induce RNA-directed DNA methylation (RdDM) through the NRPD1 pathway. To investigate their biological functions we characterized siRNAs in the endosperm and seed coat that were separated by laser capture microdissection (LCM) in reciprocal genetic crosses with an nrpd1 mutant. We also monitored the spatio-temporal activity of the NRPD1 pathway on seed development using AGO4:GFP::AGO4 (promoter:GFP::protein) reporter and promoter:GUS sensors of siRNA-mediated silencing. From these approaches we identified four distinct groups of siRNA loci that were dependent on or independent of the maternal NRPD1 allele in the endosperm or seed coat. A group of maternally expressed NRPD1-siRNA loci targets endosperm-preferred genes, including those encoding AGAMOUS-LIKE (AGL) transcription factors. Using the sensor AGL40:GUS and AGL91:GUS constructs we demonstrate that spatial and temporal expression patterns of these genes in the endosperm were regulated by the NRPD1-mediated pathway irrespective of complete silencing (AGL91) or incomplete silencing (AGL40) of these target genes. Modified expression of these siRNA-targeted genes affects seed size and we propose that the corresponding maternal siRNAs could account for parent-of-origin effects on the endosperm in interploidy and hybrid crosses. These analyses reconcile previous studies on siRNAs and imprinted gene expression during seed development.
Project description:Seed development in angiosperms requires a 2:1 maternal-to-paternal genome ratio (2m:1p) in the endosperm. When the ratio is disrupted, the seed development is impaired. Rice interploidy crosses result in endosperm failures. Here we report that the defective endosperm was associated with nonadditive expression of small RNAs and protein-coding genes. Interestingly, 24-nt siRNAs were enriched in the 5’ and 3’ flanking sequences of nonadditively expressed genes in the interploidy crosses and negatively associated with the expression of imprinted genes. Furthermore, some PRC2 gene family members and the genes for DNA methylation including OsMET1b and OsCMT3a were upregulated in the 2X4 cross but repressed in the reciprocal cross. These different epigenetic effects could lead to precocious or delayed cellularization during endosperm development. Notably, many endosperm-preferred genes including starch metabolic and storage protein genes during grain filling were associated with DNA methylation or H3K27me3 and repressed in both 2X4 and 4X2 crosses. WUSCHEL homeobox2 (WOX2)-like (WOX2L), an endosperm-preferred gene, was expressed specifically in the rice endosperm, on contrary to WOX2 expression in the Arabidopsis embryo. CRISPR/Cas9 editing of WOX2L in transgenic rice blocked starch and protein accumulation, resulting in seed abortion. In addition to gene repression, disrupting epigenetic process in the interploidy crosses also induced expression of stress-responsive genes. Thus, maintaining the 2m:1p genome ratio in the endosperm is essential for normal grain development in rice and other cereal crops.
Project description:Seed size is important to crop domestication and natural selection and is affected by the balance of maternal and paternal genomes in endosperm. Endosperm, like placenta in mammals, provides reserves to the developing embryo. Interploidy crosses disrupt the genome balance in endosperm and alter seed size. Specifically, paternal-excess crosses (2 M-CM-^W 4) delay endosperm cellularization (EC) and produce larger seeds, whereas maternal-excess crosses (4 M-CM-^W 2) promote precocious EC and produce smaller seeds. The mechanisms for responding to the parental genome dosage imbalance and for gene expression changes in endosperm are unknown. In plants, RNA polymerase IV (PolIV or p4) encoded by NRPD1a is required for biogenesis of a major class of 24-nt small interfering RNAs (also known as p4-siRNAs), which are predominately expressed in developing endosperm. Here we show that p4-siRNA accumulation depends on the maternal genome dosage, and maternal p4-siRNAs target transposable elements (TEs) and TE-associated genes (TAGs) in seeds. The p4-siRNAs correlate negatively with expression levels of AGAMOUS-LIKE (AGL) genes in endosperm of interploidy crosses. Moreover, disruption of maternal NRPD1a expression is associated with p4-siRNA reduction and AGL up-regulation in endosperm of reciprocal crosses. This is unique genetic evidence for maternal siRNAs in response to parental genome imbalance and in control of transposons and gene expression during endosperm development. 8 samples: 2x X 2x seed,leaf; 4x X 4x seed,leaf; 2x X 4x seed,leaf; 4x X 2x seed,leaf.
Project description:Seed size is important to crop domestication and natural selection and is affected by the balance of maternal and paternal genomes in endosperm. Endosperm, like placenta in mammals, provides reserves to the developing embryo. Interploidy crosses disrupt the genome balance in endosperm and alter seed size. Specifically, paternal-excess crosses (2 × 4) delay endosperm cellularization (EC) and produce larger seeds, whereas maternal-excess crosses (4 × 2) promote precocious EC and produce smaller seeds. The mechanisms for responding to the parental genome dosage imbalance and for gene expression changes in endosperm are unknown. In plants, RNA polymerase IV (PolIV or p4) encoded by NRPD1a is required for biogenesis of a major class of 24-nt small interfering RNAs (also known as p4-siRNAs), which are predominately expressed in developing endosperm. Here we show that p4-siRNA accumulation depends on the maternal genome dosage, and maternal p4-siRNAs target transposable elements (TEs) and TE-associated genes (TAGs) in seeds. The p4-siRNAs correlate negatively with expression levels of AGAMOUS-LIKE (AGL) genes in endosperm of interploidy crosses. Moreover, disruption of maternal NRPD1a expression is associated with p4-siRNA reduction and AGL up-regulation in endosperm of reciprocal crosses. This is unique genetic evidence for maternal siRNAs in response to parental genome imbalance and in control of transposons and gene expression during endosperm development.
Project description:Hybridization of diverged taxa often result in lethality or sterility. We previously described natural variation for postzygotic incompatibility in the cross of diploid Arabidopsis thaliana to Arabidopsis arenosa. Hybrid seed death in this system has a complex genetic basis, involving many non-additive interactions. While activation of AGAMOUS-LIKE genes (AGL) and Athila elements have been detected 5-8 days after pollination (DAP), the molecular basis of death remains mysterious. To address this problem, we compared 3DAP transcriptomes in interspecific hybrids from two A. thaliana ecotypes, one compatible, the other incompatible. Relative to self crosses of the respective A. thaliana seed parent, hybrids displayed differential expression of key developmental regulators in both the endosperm and maternal seed coat as well as natural variation for stress response genes. Ribosomal protein genes and a photosynthetic cluster of genes were hyperactivated, presumably in response to growth signals. Suppressing endosperm growth factor IKU1 and defense response regulators such as NON-EXPRESSOR OF PATHOGENESIS RELATED1 (NPR1) improved hybrid seed survival. Therefore, in incompatible hybrids disruption of seed development most likely initiates in the endosperm, rapidly affecting embryo and seed coat. The activation of putative POLYCOMB REPRESSIVE COMPLEX (PRC) gene targets, together with a twenty-fold reduction in expression of the FERTILIZATION INDEPENDENT SEED 2 gene, indicates a PRC role. Examination of differential gene expression of incompatible A. thaliana eco. Col-0 X A. arenosa and compatible A. thaliana eco. C24 X A. arenosa hybrid seeds plus corresponding A. thaliana and A. arenosa control crosses.