XRCC3 Is Essential For Proper Double Strand Break Repair And Homologous Recombination In Rice Meiosis

Meiosis is a critical process in eukaryotes, occupying a central role in the reproduction and life cycles of all sexually reproducing organisms. Meiosis differs from mitosis in that one round of DNA replication is followed by two sequential cell divisions, leading to the generation of four haploid cells from a single initial diploid cell. The chromosome number of the zygote derived from fertilization recovers to that of the parents. Then, meiosis is important for sexually reproducing organisms to retain the stability of their genetic materials. Moreover, genetic variations can be produced during meiosis through homologous chromosome recombination during prophase I.Many genes are involved in Homologous recombination. RAD51, a eukaryotic homolog of bacterial RecA protein, has DNA-dependent ATPase activity and facilitates strand exchange between homologous DNA molecules. RAD51 is conserved from yeast to human in both structure and function. In addition, RAD51 paralogs play important roles in the assembly and stabilization of RAD51 nucleoprotein filaments, which promote homologous pairing and strand exchange reactions in organisms ranging from yeast to vertebrates. XRCC3, a RAD51 paralog, has been characterized in budding yeast, mouse and Arabidopsis. XRCC3 seems to be involved in the strand exchange processes, but its role and interaction remain unclear.In the present study, we identified and characterized XRCC3 in rice. The rice xrcc3 mutant exhibited normal vegetative growth but complete male and female sterility. Cytological investigations revealed that homologous pairing and synapsis were severely disrupted in the mutant. Meiotic chromosomes were frequently entangled from diplotene to metaphase Ⅰ, resulting in chromosome fragmentation at anaphase Ⅰ. The immunostaining signals from yH2AX were regular, implying that double-strand break (DSB) formation was normal in xrcc3 meiocytes. However, COM1 was not detected on early prophase Ⅰ chromosomes, suggesting that the DSB end processing system was destroyed in the mutant. Moreover, abnormal chromosome localization of RAD51C, DMC1, ZEP1, ZIP4, and MER3 was observed in xrcc3. Taken together, the results suggest that XRCC3 plays critical roles in both DSB repair and homologous chromosome recombination during rice meiosis.