Meiosis is a fundamental process in eukaryote reproduction, generating diversity in progeny. During meiosis, homologous chromosomes pair and undergo reciprocal crossovers. Crossovers are tightly regulated; an obligate exchange always forms per chromosome pair, but it is rare to observe more than three crossovers and multiple crossovers are widely distributed in most eukaryotes due to a phenomenon called ‘crossover interference’. In Arabidopsis, crossover positions and interference can be explained by a diffusion-mediated coarsening model. Large, approximately evenly-spaced foci of the pro-crossover E3 ligase HEI10 are proposed to grow and concentrate to crossover sites, at the expense of smaller, closely-spaced HEI10 clusters along a chromosome pair. However, the molecular mechanisms that regulate crossover patterning through the dynamics of HEI10 remain incompletely elucidated. We have performed a forward genetic screen in Arabidopsis to identify new regulators of crossover positioning, and isolated high crossover rate3 (hcr3) as a dominant-negative mutant in J3 encoding a J domain–containing HSP40 co-chaperone. HSP40 co-chaperones monitor protein molecular status, provide substrate specificity, and enhance HSP70 ATPase protein activities. Through a comprehensive array of cytogenetic, genetic, genomic, biochemical, and modeling approaches, we demonstrated that J3 facilitates proteolysis of HEI10 via its ubiquitination and SUMOylation by recruiting HSP70 chaperones. hcr3, j3, transgenic expression of a dominant-negative allele of J3, and meiotic knockdown of HSP70 genes elevate crossovers genome-wide by increasing HEI10 abundance. Our findings provide new mechanistic insight into how a network of HSP40-HSP70 chaperones mediates meiotic crossover interference and thereby limits crossover numbers.