Chromosomal collinearity drives meiotic instability in Brassica autoallopolyploid

Polyploidization is a pivotal process in plant evolution, serving as a major driving force for genome diversification and adaptive potential. However, the meiotic behavior of autoallopolyploid remains poorly understood. Here, we analyzed the meiotic behavior of a Brassica autoallohexaploid (AⁿAⁿCⁿCⁿC^oC^o) derived from B. napus (AⁿAⁿCⁿCⁿ) and B. oleracea (C^oC^o), using fluorescence in situ hybridization (FISH). The addition of the C^o genome from B. oleracea induced A-C homoeologous pairing in 78.5% of pollen mother cells (PMCs) in the S₀ generation. The prevalence of univalents, autotrivalents, and homoeologous pairings at diakinesis I strongly correlated with irregular chromosomal segregation at anaphase I. The frequency of homoeologous pairing was positively correlated with the extent of chromosomal collinearity. The emergence of a relatively stable euploid line in the S₄ generation suggests that successive selfing enhances meiotic stability in autoallohexaploids. Subsequently, we constructed a gene co-expression network based on differentially expressed genes (DEGs) between the stabilized S₄ line and the S₀ generation, which highlighted hub genes potentially governing meiotic stability. Together, these findings provide new insights into meiotic stability in autoallohexaploid and offer valuable knowledge for polyploid breeding and the improvement of genomic stability in Brassica crops.