A major quantitative trait locus on chromosome A9, BnaPh1, controls homoeologous recombination in Brassica napus

Abstract

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.

A duplicated copy of the meiotic geneZIP4preserves up to 50% pollen viability and grain number in polyploid wheat

“…Such studies will also need to confirm whether different TaZIP4 B2 alleles exhibit variable phenotypes sensitive to temperature change. Natural variation in the meiotic phenotypes has been reported for some meiotic genes in other polyploids (Jenczewski et al, 2003;Liu et al, 2006;Yant et al, 2013;Morgan et al, 2020;Seear et al, 2020;Higgins et al,2020). The new approach for analysing pollen presented in this study can be used in future TaZIP4-B2 studies to screen landrace diversity mapping populations (Wingen et al, 2017), carrying different TaZIP4-B2 alleles for variable phenotypes, with variable sensitivity to temperature.…”

“…Recent studies have implicated at least eight different autotetrapolyploid Arabidopsis meiotic genes in the meiotic stabilisation process (Yant et al, 2013), with specific alleles in one of these genes, ASY3, being highlighted in two further studies (Morgan et al, 2020;Seear et al, 2020). Allopolyploid Brassica studies have also reported a number of loci exhibiting natural variation in their ability to affect homoeologous pairing and crossover (Jenczewski et al, 2003;Liu et al, 2006;Higgins et al, 2020). Thus, these studies assessed the effects of natural gene variation on the meiotic process.…”

Homoeologous exchanges in allopolyploids: how Brassica napus established self‐control!

“…Schematic representation of logic behind the QTL mapping approach implemented by Higgins et al . (2021; https://doi.org/10.1111/nph.16986) in the recently published article in New Phytologist . Nascent or resynthesized oilseed rape tolerates homoeologous exchanges (HEs) that the selection of BnaPh1 during the evolution of Brassica napus helps to reduce.…”

“…Although the regions around the minor QTLs (BnaA3 and BnaC7) identified by Higgins et al . (2021) include genes encoding another MutS Homologue protein, MSH3, it is uncertain whether these genes may be causal for the QTLs. First, MSH3 protein has an affinity for loop‐outs of various sizes (Culligan & Hays, 2000 and references cited therein), rather than for base/base mismatches.…”

Untangling structural factors and evolutionary drivers in nascent polyploids

“…Similarly, other genes have been described as implicated in homoeologous pairing control via dosage or allele effect, such as MSH4 (Gonzalo et al ., 2019). BnaPH1 and PrBn have additionally been shown to reduce homoeologous pairing (Jenczewski et al ., 2003; Higgins et al ., 2020).…”