The occurrence,inheritance,and segregation of complex genomic structural variation in synthetic Brassica napus

"Synthetic"allopolyploids recreated by interspecific hybridization play an important role in providing novel genomic variation for crop improvement.Such synthetic allopolyploids often undergo rapid genomic structural variation(SV).However,how such SV arises,is inherited and fixed,and how it affects important traits,has rarely been comprehensively and quantitively studied in advanced generation synthetic lines.A better understanding of these processes will aid breeders in knowing how to best utilize synthetic allopolyploids in breeding programs.Here,we analyzed three genetic mapping populations(735 DH lines)derived from crosses between advanced synthetic and conventional Brassica napus(rapeseed)lines,using whole-genome sequencing to determine genome composition.We observed high tolerance of large structural variants,particularly toward the telomeres,and preferential selection for balanced homoeologous exchanges(duplication/deletion events between the A and C genomes resulting in retention of gene/chromosome dosage between homoeologous chromosome pairs),including stable events involving whole chromosomes("pseudoeuploidy").Given the experimental design(all three populations shared a common parent),we were able to observe that parental SV was regularly inherited,showed genetic hitchhiking effects on segregation,and was one of the major factors inducing adjacent novel and larger SV.Surprisingly,novel SV occurred at low frequencies with no significant impacts on observed fertility and yield-related traits in the advanced generation synthetic lines.However,incorporating genome-wide SV in linkage mapping explained significantly more genetic variance for traits.Our results provide a framework for detecting and understanding the occurrence and inheritance of genomic SV in breeding programs,and support the use of synthetic parents as an important source of novel trait variation.

The identification of presence/absence variants associated with the apparent differences of growth period structures between cultivated and wild soybeans

The cultivated soybean（Glycine max（L.） Merr.） was distinguished from its wild progenitor Glycine soja Sieb.＆ Zucc.in growth period structure,by a shorter vegetative phase（V）,a prolonged reproductive phase（R） and hence a larger R/V ratio.However,the genetic basis of the domestication of soybean from wild materials is unclear.Here,a panel of 123 cultivated and 97 wild accessions were genotyped using a set of 24 presence/absence variants（PAVs） while at the same time the materials were phenotyped with respect to flowering and maturity times at two trial sites located at very different latitudes.The major result of this study showed that variation at PAVs is informative for assessing patterns of genetic diversity in Glycine spp.The genotyping was largely consistent with the taxonomic status,although a few accessions were intermediate between the two major clades identified.Allelic diversity was much higher in the wild germplasm than in the cultivated materials.A significant domestication signal was detected at 11 of the PAVs at 0.01 level.In particular,this study has provided information for revealing the genetic basis of photoperiodism which was a prominent feature for the domestication of soybean.A significant marker-trait association with R/V ratio was detected at 14 of the PAVs,but stripping out population structure reduced this to three.These results will provide markers information for further finding of R/V related genes that can help to understand the domestication process and introgress novel genes in wild soybean to broaden the genetic base of modern soybean cultivars.

Snapshot of Structural Variations in the Tibetan Wild Boar Genome at Single-Nucleotide Resolution

Genomic structural variations （SVs）, particularly insertions, deletions and inversions, can contribute to the heterogeneity of millions of nucleotides within a genome, and are likely to make an important contribution to biological diversity and phenotypic variation （Alkan et al., 2011; Bickhart and Liu, 2014）. With the rapid development of the next-generation sequencing technologies and the new assembly methodolo- gies, the multiple de novo assemblies of genomes within a species allow researchers to explore more detailed SV maps （Li et al., 2011）. Compared with the traditional read depth algorithm using the whole-genome resequencing approach and array-based technologies （Baker, 2012; Wang et al., 2012;

Structural and Expressional Variation Analyses of Mitochondrial Genomes Reveal Candidate Transcripts for the S^V Cytoplasmic Male Sterility in Wheat(Triticum aestivum L.)

Common wheat （Triticum aestivum L.） is one of the most important crops, and intra-specific wheat hybrids have obvious heterosis in yield and protein quality. Therefore, utilization of hybrid wheat varieties offers an effective way to increase yield and nutrition. Cytoplasmic male sterility （CMS） systems are a useful genetic tool for hybrid crop breeding, and are ideal models for studying the genetic interaction and cooperative function of mitochondrial and nuclear genomes in plants （Schnable and Wise, 1998; Hanson and Bentolila, 2004）.

Unlocking plant metabolic diversity: A (pan)- genomic view

Plants produce a remarkable diversity of structurally and functionally diverse natural chemicals that serve as adaptive compounds throughout their life cycles.However,unlocking this metabolic diversity is significantly impeded by the size,complexity,and abundant repetitive elements of typical plant genomes.As genome sequencing becomes routine,we anticipate that links between metabolic diversity and genetic variation will be strengthened.In addition,an ever-increasing number of plant genomes have revealed that biosynthetic gene clusters are not only a hallmark of microbes and fungi;gene clusters for various classes of compounds have also been found in plants,and many are associated with important agronomic traits.We present recent examples of plant metabolic diversification that have been discovered through the exploration and exploitation of various genomic and pan-genomic data.We also draw attention to the fundamental genomic and pan-genomic basis of plant chemodiversity and discuss challenges and future perspectives for investigating metabolic diversity in the coming pan-genomics era.

3D genome structural variations play important roles in regulating seed oil content of Brassica napus

Dissecting the complex regulatory mechanism of seed oil content(SOC)is one of the main research goals in Brassica napus.Increasing evidence suggests that genome architecture is linked to multiple biological functions.However,the effect of genome architecture on SOC regulation remains unclear.Here,we used high-throughput chromatin conformation capture to characterize differences in the three-dimen-sional(3D)landscape of genome architecture of seeds from two B.napus lines,N53-2(with high SOC)and Ken-C8(with low SOC).Bioinformatics analysis demonstrated that differentially accessible regions and differentially expressed genes between N53-2 and Ken-C8 were preferentially enriched in regions with quantitative trait loci(QTLs)/associated genomic regions(AGRs)for SOC.A multi-omics analysis demonstrated that expression of SOC-related genes was tightly correlated with genome structural varia-tions in QTLs/AGRs of B.napus.The candidate gene BnaA09g48250D,which showed structural variation in a QTL/AGR on chrA09,was identified byfine-mapping of a KN double-haploid population derived from hybridization of N53-2 and Ken-C8.Overexpression and knockout of BnaA09g48250D led to significant in-creases and decreases in SOC,respectively,in the transgenic lines.Taken together,our results reveal the 3D genome architecture of B.napus seeds and the roles of genome structural variations in SOC regulation,enriching our understanding of the molecular mechanisms of SOC regulation from the perspective of spatial chromatin structure.