Chaperone-mediated Control of Meiotic Crossover Number in Arabidopsis thaliana

The number of meiotic crossovers is limited and tends to be 1–2 between a pair of homologous chromosomes, despite the induction of excessive initiating DNA double strands breaks (DSBs). In most eukaryotes, approximately 85% of crossovers depend on the conserved ZMM repair pathway, including a group of pro-crossover ZMM proteins and MutLγ (MLH1–MLH3) complex. However, anti-crossover factors that counteract with pro-crossover factors in the ZMM pathway remain largely unexplored. We identified HIGH CROSSOVER RATE3 (HCR3) encoding J3, a HSP40 chaperone that limits ZMM-dependent crossovers using forward genetic screen and fluorescent crossover reporter system in Arabidopsis. The hcr3 harbors a missense mutation in zinc-finger domain of J3, which increases crossover frequency in a dominant negative manner. Using genome-wide crossover analyses we observed that hcr3 elevates ZMM-dependent crossovers in distal chromosomal regions in both inbred and hybrid plants. Consistently, MLH1 and dosage-sensitive E3 ligase HEI10 foci numbers are increased in hcr3. HCR3 interacts with ZMM proteins, HEI10, PTD and MSH5. I will present a possible model for HCR3/J3 in which HCR3/J3-containing chaperones mediate ZMM proteolysis and limit the number of crossovers.2