Separable roles of the DNA damage response kinase Mec1(ATR) and its activator Rad24(RAD17) within the regulation of meiotic recombination

During meiosis, programmed DNA double-strand breaks (DSBs) are formed by the topoisomerase-like enzyme, Spo11, activating the DNA damage response (DDR) kinase Mec1ATR via the checkpoint clamp loader, Rad24(RAD17). At single loci, loss of Mec1 and Rad24 activity alters Spo11-dependent DSB formation and recombination outcome, but their genome-wide roles have not been examined in detail. Here we utilise two distinct methods to characterise the roles Mec1 and Rad24 play in meiotic recombination - deletion of the mismatch repair protein, Msh2, and control of meiotic prophase length via regulation of the Ndt80 transcription factor - to enable genome-wide mapping of meiotic progeny. In line with previous studies, we observe a reduction in the frequency of recombination upon deletion of RAD24 - driven by a shortened prophase. By contrast, loss of Mec1 function increases recombination frequency, consistent with its role in DSB trans-interference. Despite this difference in recombination rate, complex, multi-chromatid events initiated by closely spaced DSBs - a rare event in wild type cells - occur more frequently in the absence of either Rad24 or Mec1, suggesting a loss of spatial regulation at the level of DSB formation. We further demonstrate that Mec1 and Rad24 also have important, yet distinct, roles in the spatial regulation of crossovers (COs). Specifically, excess DSBs forming in the absence of Mec1 are disproportionately channelled into the non-crossover (NCO) and non-interfering CO pathways, reducing the global strength of interference without an explicit change in the frequency of interfering COs. In direct contrast, loss of Rad24 weakens interference via a reduction in the apparent number of interfering COs - similar, but less extreme, to the phenotype of 9ZMM9 mutants such as zip3Δ. Collectively, our results highlight novel and unique roles for Rad24 within meiotic recombination - beyond those mediated by activation of Mec1 - and describe new roles for the DDR in several important aspects of meiosis.