Chromatin Landscape of Meiotic Recombination in Maize

Meiotic recombination is initiated by programed double-strand breaks (DSBs) in chromosomal DNA and results in crossovers (COs) and non-crossovers (NCOs). In many organisms, there is an excessive number of meiotic DSBs to the number of COs, but it is not well understood how this process is regulated and which DSBs become COs. In the B73 inbred of maize, ~500 DSBs are observed in mid zygotene which lead to ~20 COs. These DSBs are evenly distributed along chromosomes including pericentromeric and centromeric regions. However, CO distribution does not follow the DSB distribution. COs in B73 are enriched in distal chromosome regions that are known to be euchromatic. COs are suppressed in proximal regions containing the pericentromeric and centromeric regions, which are generally heterochromatic. In the CML228 inbred of maize, there are only ~200 observed DSBs, which is roughly half the number of DSBs in B73. These DSBs result in only 11 COs. Unlike COs in B73, CML228 COs are located in the proximal regions of the chromosome. We are using these two maize inbreds with diverse DSBs and CO distributions to investigate the dynamics of recombination events in euchromatic and heterochromatic chromosomal regions and to understand how this distribution is formed. Results of our experiments indicate that the occurrence of DSB events in euchromatic and heterochromatic chromosomal regions do not differ significantly between these two inbreds. Instead, they can be attributed to processes of DSB repair which occur in later stages of meiotic prophase I.