Genome-wide crossover analysis in the holocentric pantry moth reveals strong crossover assurance and interference during spermatogenesis

Meiosis relies on programmed DNA double-strand breaks (DSBs) to initiate recombination between homologous chromosomes. Only a fraction of these breaks mature into crossovers (COs), creating the chiasmata essential for physically linking homologs and ensuring their accurate segregation in meiosis I. Errors in CO number or placement underlie a large fraction of human infertility and aneuploidies, yet how DSBs are designated to become COs and how the mechanisms ensuring COs form on all chromosomes (CO assurance) are not well understood, particularly in systems with a large number of chromosomes. Here, we investigate CO formation in the pantry moth, Plodia interpunctella , a novel invertebrate model system with n = 31 chromosomes. Using a combination of sequencing approaches, Oligopaints FISH, and statistical Weinstein tetrad analysis, we find robust CO assurance and interference in Plodia , with most chromosomes harboring only a single distal CO and few bivalents lacking COs. We employ CUT&RUN, ATAC-seq, and RNA-seq to profile the epigenomic landscape in Plodia testes, revealing that the distal chromosome arms in which COs form are enriched for heterochromatin and devoid of accessible chromatin, suggesting a bias for COs to form in repressed regions in the genome. These studies pave the way for future work diving deeper into the molecular regulation of CO formation in Plodia and other systems, in which the large number of chromosomes may be the key to revealing novel insights about CO regulation.