Mechanisms of Meiotic Prophase are Disrupted in Neopolyploid Maize

Cycles of DNA multiplication followed by reshuffling and loss define the evolutionary history of eukaryotes, particularly plants. On a whole genome level, polyploidization initiates this cycle. Diploidization begins immediately and can continue over the course of millions of years. Epigenetic reprogramming, gene expression changes, as well as significant rearrangement and loss of DNA are all known aspects of diploidization. The success of a nascent polyploid depends on the outcomes of these processes. Meiotic recombination is a key mechanistic determinant of these outcomes. The chromosomal interactions of pairing and recombination can directly lead to DNA rearrangements or losses and are impacted by epigenetic changes. Though recombination shapes the diploidization landscape, the impact of polyploidization on recombination itself is unknown. Are meiotic processes quantifiably different in neopolyploid plants than in their diploid relatives? To begin, we evaluated the meioses of three neopolyploid maize lines. Early in prophase I, recombination is initiated by the formation of double strand breaks (DSBs) in the DNA. These DSBs are resected, resulting in single-stranded overhangs of DNA which function in a homology search process. By the end of prophase I, DSBs are repaired either as crossovers (COs) or non-crossovers. In neopolyploid maize, we observe an increase in the peak number of DSBs, as well as an anomalous persistence of DSBs in later prophase I. We also observe COs between non-homologous chromosomes. These lines of evidence indicate a decoupling of the meiotic processes of pairing and recombination following polyploidization and lead to potential mechanistic underpinnings of diploidization.