The SUN Domain Proteins OsSUN1 and OsSUN2 Play Critical but Partially Redundant Roles in Meiosis.

During meiosis, Sad1/UNC-84 (SUN) domain proteins play conserved roles in promoting telomere bouquet formation and homologous pairing across species. Arabidopsis () AtSUN1 and AtSUN2 have been shown to have overlapping functions in meiosis. However, the role of SUN proteins in rice () meiosis and the extent of functional redundancy between them remain elusive. Here, we generated single and double mutants of and in rice using genome editing. The double mutant showed severe defects in telomere clustering, homologous pairing, and crossover formation, suggesting that OsSUN1 and OsSUN2 are essential for rice meiosis. When introducing a mutant allele of (), which encodes a topoisomerase initiating homologous recombination, into the mutant, we observed a combined - and -like phenotype, demonstrating that OsSUN1 and OsSUN2 promote bouquet formation independent of OsSPO11-1 but regulate pairing and crossover formation downstream of OsSPO11-1. Importantly, the single mutant had a normal phenotype, but meiosis was disrupted in the mutant, indicating that OsSUN1 and OsSUN2 are not completely redundant in rice. Further analyses revealed a genetic dosage-dependent effect and an evolutionary differentiation between and These results suggested that OsSUN2 plays a more critical role than OsSUN1 in rice meiosis. Taken together, this work reveals the essential but partially redundant roles of OsSUN1 and OsSUN2 in rice meiosis and demonstrates that functional divergence of SUN proteins has taken place during evolution.