Project description:Illumina mRNA-Seq is comparable to microarray analysis for transcript quantification but has increased sensitivity and, importantly, the potential to distinguish between homoeologous genes in polyploids. Using a novel curing process, we adapted a reference sequence that was a consensus derived from ESTs from both Brassica A and C genomes to one containing A and C genome versions for each of the 94,558 original unigenes. We aligned reads from Brassica napus to this cured reference, finding 38% more reads mapping in resynthesised lines and 28% in natural lines. Where the A and C versions differed at single nucleotide positions, termed inter-homoeologue polymorphisms (IHPs), we were able to apportion expression in the polyploid to the A or C genome homoeologues. 43,761 unigenes contained at least one IHP, with a mean frequency of 10.5 per kb unigene sequence. 6,350 of the unigenes with IHPs were differentially expressed between homoeologous gene pairs in resynthesised B. napus. 3,212 unigenes showed a similar pattern of differential expression across a range of natural B. napus crop varieties and, of these, 995 were in common with resynthesised B. napus. Functional classification showed over-representation in gene ontology categories not associated with dosage-sensitivity.
Project description:Polyploidy has played an extensive role in the evolution of flowering plants. Allopolyploids, with subgenomes containing duplicated gene pairs called homeologs, can show rapid transcriptome changes including novel alternative splicing (AS) patterns. The extent to which abiotic stress modulates AS of homeologs is a nascent topic in polyploidy research. We subjected both natural and resynthesized lines of polyploid Brassica napus, along with the progenitors B. rapa and B. oleracea, to infection with the fungal pathogen Sclerotinia sclerotiorum. RNA-seq analyses revealed widespread divergence between polyploid subgenomes in both gene expression and AS patterns. Resynthesized B. napus displayed significantly more A and C subgenome biased homeologs under pathogen infection than during uninfected growth. Differential AS (DAS) in response to infection was highest in natural B. napus (12,709 DAS events) and lower in resynthesized Brassica napus (8,863 DAS events). Natural B. napus had more up-regulated events and fewer down-regulated events. There was a global expression bias towards the B. oleracea-derived (C) subgenome in both resynthesized and natural B. napus, enhanced by widespread non-parental downregulation of the B. rapa-derived (A) homeolog. In the resynthesized B. napus specifically, this resulted a disproportionate C subgenome contribution to pathogen defense response, characterized by biases in both transcript expression levels and the proportion of induced genes. Our results elucidate the complex ways in which Sclerotinia infection affects expression and AS of homeologous genes in natural and resynthesized B. napus, and indicate that abiotic stress can influence the evolution of homeologous genes in polyploids.
Project description:Many crop species have polyploid genomes that are unlikely to be sequenced to a high standard in the near future, representing a barrier to genomics-based breeding. As an exemplar, we sequenced the leaf transcriptome to analyse both sequence variation1 and transcript abundance across a mapping population of oilseed rape (Brassica napus), together with representatives of ancestors of the parents of the population. Twin SNP linkage maps were constructed, comprising 23,037 markers in all. These were used to analyse the genome for alignment to that of a related species, Arabidopsis thaliana, and to genome sequence assemblies of the progenitor species of B. napus. Methods were developed that enabled us to detect genome rearrangements and track inheritance of genomic segments, including the outcome of an inter-specific cross. This transformative advance, enabling economical high-resolution dissection of the genomes of most, if not all, crop species, will enable us to understand the genetic consequences of breeding and domestication, and will underpin the development of efficient predictive breeding strategies.
Project description:We establish global maps of regulatory elements and chromatin states and their dynamics, for both the whole and subgenomes of four tissue types (young leaf, flower bud, silique, and root) of two B. napus lines. Approximately 52 % of the genome was annotated with different epigenomic signals. We also uncover a new bivalent chromatin state in B. napus and suggest its key roles in regulating tissue-specific gene expression. Furthermore, we observe that different types of duplicated genes have differential patterns of histone modifications, DNA methylation, and selection pressures. Together, we provide valuable epigenetic data resources of allopolyploid B. napus and reveal the central role of epigenomic information in understanding transcriptional regulation in polyploid plants.
Project description:We establish global maps of regulatory elements and chromatin states and their dynamics, for both the whole and subgenomes of four tissue types (young leaf, flower bud, silique, and root) of two B. napus lines. Approximately 52 % of the genome was annotated with different epigenomic signals. We also uncover a new bivalent chromatin state in B. napus and suggest its key roles in regulating tissue-specific gene expression. Furthermore, we observe that different types of duplicated genes have differential patterns of histone modifications, DNA methylation, and selection pressures. Together, we provide valuable epigenetic data resources of allopolyploid B. napus and reveal the central role of epigenomic information in understanding transcriptional regulation in polyploid plants.
Project description:We establish global maps of regulatory elements and chromatin states and their dynamics, for both the whole and subgenomes of four tissue types (young leaf, flower bud, silique, and root) of two B. napus lines. Approximately 52 % of the genome was annotated with different epigenomic signals. We also uncover a new bivalent chromatin state in B. napus and suggest its key roles in regulating tissue-specific gene expression. Furthermore, we observe that different types of duplicated genes have differential patterns of histone modifications, DNA methylation, and selection pressures. Together, we provide valuable epigenetic data resources of allopolyploid B. napus and reveal the central role of epigenomic information in understanding transcriptional regulation in polyploid plants.
Project description:We establish global maps of regulatory elements and chromatin states and their dynamics, for both the whole and subgenomes of four tissue types (young leaf, flower bud, silique, and root) of two B. napus lines. Approximately 52 % of the genome was annotated with different epigenomic signals. We also uncover a new bivalent chromatin state in B. napus and suggest its key roles in regulating tissue-specific gene expression. Furthermore, we observe that different types of duplicated genes have differential patterns of histone modifications, DNA methylation, and selection pressures. Together, we provide valuable epigenetic data resources of allopolyploid B. napus and reveal the central role of epigenomic information in understanding transcriptional regulation in polyploid plants.
Project description:mRNA expression profiling of the embryo, endosperm (micropylar, peripheral, chalazal), and seed coat (outer, inner, chalazal, chalazal proliferating tissue) of the developing Brassica napus seed. Tissues were isolated using laser microdissection (LMD) from Brassica napus seeds at the globular, heart, and mature green stages of seed development.