The Functional Analysis Of OsMRE11 In Rice Meiosis And Mitosis

Meiosis and mitosis are two important processes in organisms.Mitosis plays a critical role in maintaining individual growth and development.Meiosis guarantees the stability of the chromosome number in different generations of sexual reproduction organism,also provides the genetic materials for creating variation during the sexual reproduction.Double-strand break(DSB)as an important DNA damage has serious influence in both meiosis and mitosis.MRE11 is an important gene associated with cell division.It has been reported that MRE11 has an important relationship with DNA damage repair.Also,the MRE11-RAD50-NBS1(MRN)complex takes part in DNA damage repair.The defects of any one of these three proteins would has serious impact.So far,there are a few studies related toMRE11 gene functions in regulating rice mitosis and meiosis.We focus on MRE11 through phenotypic analysis of different allelic mutants and protein function research.We were expected to explore the role of MRE11 protein in DSB repair and find out the functional differences between meiosis and mitosis.In this study,we identified three OsMRE11 allelic mutants through T-DNA insertion and CRISPR/CAS9 system.We named them Osmrell-1,Osmre11-2 and Osmrell-3,respectively.Based on the observation and analysis of vegetative growth and reproductive growth.We found gametogenesis defects and resulted in sterility of mutant plants.Cytological analysis showed that mutant abnormal chromosome behavior in the Osmrell pollen mother cells(PMCs).Homologous recombination were abnormal,and DSBs repair was interrupted severely.From diakinesis to metaphase I,meiotic chromosomes entangled and developed into chromosome aggregates.Subsequently,those chromosome aggregates were pulled apart toward cell poles,and then a lot of chromosome fragments remained in the middle of the cell.Unequal separation genetic materials and fragmented chromosomes leads to incomplete genetic information in gametes,further giving rise to sterility phenotype of Osmrell mutants.These abnormal phenotypes are consistent with previous findings obtained from rice MRE11RNAi.lines.Further immunostaing assay showed that several key meiotic proteins,including DMC1,HE110 and ZEP1 were not loaded normally onto chromosomes in Osmrell mutants.However,the localization of,yH2AX.PAIR2 and PAIR3 to be normal.These results confirmed that OsMRE11 meiosis of the main function is to DSB repair and promote the synaptonemal complex assembly.Based on three different allelic mutants vegetative growth we observed Osmrell-1 and Osmrell-2 were significantly inhibited and show apparent dwarf phenotype.Plant height is approximately 50%of the wild type.On the contrary,the vegetative growth of Osmre11-3 is normal.We took a comparative analysis on three mutants and found bases deletion resulting in frameshift mutation.Especially,the truncated protein of Osmrell-2 and Osmrell-3 differ in 29 amino acids.We hypothesized that the sequence of 29 amino acids is mitotic control site in OsMRE11.In conclusion,we observed different allelic gene mutation pheaotype and analysis of protein structure,proved that OsMRE11 modulate meiosis base on auxocyte participates in homologous recombination process.This regulation function depends on the general OsMRE11 protein function without site discrepancy.While the important role of OsMRE11 in the mitosis may involved in amino acid site difference.The precise mechanism of OsMRE11 needs to be further explored.