Crossover (CO) formation between homologous chromosomes is essential for genetic diversity and accurate meiotic chromosome segregation. This process involves two key steps: the designation of a subset of meiotic double-strand breaks to CO-designated sites and subsequent CO resolution by Holliday junction (HJ) resolvase. However, how these steps are functionally coupled remains elusive. Here, we showed that COSA-1, essential for CO designation, directly interacts with the SLX-4 scaffold protein,