Genetic Regulation Of Meiosis In Brassica Napus

Meiosis plays an important role in plant reproduction, in which homologous chromosomes pairing and recombination happened. Whole genome doubling(WGD) is a great challenge to homologous chromosome paring and separating correctly in plant polyploids. To adapt to this genomic change, some key variations would be reserved during the process of its formation and evolution. Brassica napus(AACC, 2n=38) is an allotetraploid with multiple origin. Different varieties with different genetic background or from different breeding programs would have different meiosis stability. Here, we investigated the chromosome laggards at anaphase I of meiosis and pollen fertility in 189 Brassica napus varieties/inbred lines worldwide and performed the whole genome associated mapping studies(GWAS). In addition, the differentiation between A genome within Brasssica rapa and B. napus were analyzed based on whole genome resequencing of 8 B. rapa and 20 B. napus. Main results are described as follows:(1) Chromosome laggards were found widespread in different varieties of B. napus. On average, 32.5% pollen mother cells(PMCs) were fo und with chromosome laggards at cell plate at meiotic anaphase I which is under a skewed distribution in 189 varieties. There are more than 90% varieties have less than 50% PMCs with laggards. However, there are also 5 varieties shown more than 80% PMCs with chromosome laggards.(2) The pollen fertility varied largely in different environment and has weak relationships with chromosome laggards found in meiosis I. There is more than 80% varieties shown pollen fertility between 90-100%. The correlation coefficient between chromosome laggards and pollen fertility is 0.237. The abnormal separation of homologous chromosome during meiosis might not the only reason for poor pollen fertility.(3) No SNP was detected significantly associated with chromosome laggards, but several SNPs were found significantly associated with pollen fertility in different environments. In the regions where these SNP located, five meiosis related genes were found including SYN3, MRE11, MSH4, RAD51 C and FIDGETIN L1 which all have known function in chromatids cohesion, DSB formation, DSB repair and crossover formation.(4) Whole genome Fst scan found that there are 361 chromosome regions in A genome of B. napus shown significantly positive selection. In 100 regions with highest Fst value, 198 genes were found which have function mainly in cell components synthesize, organ formation and process, reproduction metabolism and etc. Interesting, four meiosis gene were also found in these regions including SMC, FIDGETIN L1, RAD51 B and ATM.