Search

Summary: Ensuring faithful homologous recombination in allopolyploids is essential to maintain optimal fertility of the species. Variation in the ability to control aberrant pairing between homoeologous chromosomes in Brassica napus has been identified. The current study exploited the extremes of such variation to identify genetic factors that differentiate newly resynthesised B. napus, which is inherently unstable, and established B. napus, which has adapted to largely control homoeologous recombination.A segregating B. napus mapping population was analysed utilising both cytogenetic observations and high‐throughput genotyping to quantify the levels of homoeologous recombination.Three quantitative trait loci (QTL) were identified that contributed to the control of homoeologous recombination in the important oilseed crop B. napus. One major QTL on BnaA9 contributed between 32 and 58% of the observed variation. This study is the first to assess homoeologous recombination and map associated QTLs resulting from deviations in normal pairing in allotetraploid B. napus.The identified QTL regions suggest candidate meiotic genes that could be manipulated in order to control this important trait and further allow the development of molecular markers to utilise this trait to exploit homoeologous recombination in a crop. See also the Commentary on this article by Sourdille & Jenczewski, 229: 3041–3043. [ABSTRACT FROM AUTHOR]

Summary: Camelina neglecta is a diploid species from the genus Camelina, which includes the versatile oilseed Camelina sativa. These species are closely related to Arabidopsis thaliana and the economically important Brassica crop species, making this genus a useful platform to dissect traits of agronomic importance while providing a tool to study the evolution of polyploids. A highly contiguous chromosome‐level genome sequence of C. neglecta with an N50 size of 29.1 Mb was generated utilizing Pacific Biosciences (PacBio, Menlo Park, CA) long‐read sequencing followed by chromosome conformation phasing. Comparison of the genome with that of C. sativa shows remarkable coincidence with subgenome 1 of the hexaploid, with only one major chromosomal rearrangement separating the two. Synonymous substitution rate analysis of the predicted 34 061 genes suggested subgenome 1 of C. sativa directly descended from C. neglecta around 1.2 mya. Higher functional divergence of genes in the hexaploid as evidenced by the greater number of unique orthogroups, and differential composition of resistant gene analogs, might suggest an immediate adaptation strategy after genome merger. The absence of genome bias in gene fractionation among the subgenomes of C. sativa in comparison with C. neglecta, and the complete lack of fractionation of meiosis‐specific genes attests to the neopolyploid status of C. sativa. The assembled genome will provide a tool to further study genome evolution processes in the Camelina genus and potentially allow for the identification and exploitation of novel variation for Camelina crop improvement. [ABSTRACT FROM AUTHOR]

Information on genetic diversity and population structure is needed for continued improvement in Brassica napus L. A total of 169 B. napus lines, collected between 1970 and 2000 in Australia, Canada, China, Europe, Japan, Pakistan, and South Korea, were genotyped with 84 simple sequence repeat markers. Nei's unbiased genetic diversity (H) and Shannon's information index (SI) showed that genetic diversity was highest among lines from Europe followed by South Korea, Japan, China, and Pakistan while lines from Australia and Canada had the lowest diversity. Pairwise comparison of the populations using Nei's genetic identity (I) and genetic distance (D) showed greater differentiation between Australia and Canada versus China and Pakistan. Accessions from South Korea and Japan were most similar, confirming an historical exchange of germplasm. The analysis of unique alleles and allele richness revealed that the Pakistani population was the richest followed by Europe and South Korea. Analysis of molecular variance revealed that 9% of the variation was accounted for by geographical region and 91% by lines. Both Structure and principal coordinate analyses indicated two subpopulations in the collection confirming separation of genotypes due to growth habit adaptation. Information on B. napus genotypes containing unique alleles is valuable for breeding programs in different parts of the world seeking to improve agronomic traits and adaptability. [ABSTRACT FROM AUTHOR]