The Molecular Mechanism Of OsFANCM In Regulating Rice Recombination

Meiosis is a special type of cell division in the process of sexual reproduction in eukaryotes.Homologous recombination is a very critical core event in meiosis.It is paired to form bivalents.Homologous recombination,which establishes chiasmata between pairs of homologs,ensures its proper separation,and generates genetic diversity by exchanging the genetic material between homologous chromosomes.In the process of crop breeding,the excellent allelic variation of genes is integrated into the same genetic background through genetic recombination,to complete the breeding of new varieties.Increasing the frequency of recombination helps to break the genetic burden of undesirable genes,while improving the efficiency of fixing good allelic variation and speeding up the breeding process.The AtFANCM gene has been cloned in Arabidopsis.The mutation of AtFAANCM can significantly increase crossovers(COs)number,but related studies have not been reported in food crops.In the present study,we obtained OsFAANCM gene by homologous alignment.And we got two T-DNA insertion mutants named Osfancm-1 and Osfancm-2 from rice insertion mutant libraries.Compared with the wild type,the mutants had no significant effect on vegetative growth and reproductive growth.Cytological observations revealed that the mutants were not significantly different from the wild type at various stages during meiosis.Meanwhile,the immunostaining signals of meiosis specific proteins(?H2AX,OsCOM1,OsZIP4 and OsHEI1O)were normally formed in the pollen mother cells of Osfancm,indicating that the mutants had normal meiosis.Previous studies have shown that unequal chromosome segregation was observed in Oshei10,due to the decrease of the COs number between homologous chromosomes,finally leading to gametes abortion.However,in the Osfancm/Oshei10 double mutant,12 bivalents arranged neatly on the equatorial plate at metaphase I and the number of COs increased significantly compared with Oshei10.The fertility of the plants was finally restored.Moreover,we found that the mutations of OsFANCM can increase the recombination frequency.Compared with the wild type,the recombination frequency of the three segments of chromosomes were increased by 1.5,2.6 and 1.7 times respectively.In Osfancm,compared to the wild type,the number of OsHEI10 bright foci did not increase,indicating class II COs might increase.Therefore,Osfancm/Oshei10/Osmus81 was constructed.In the triple mutant,12 bivalents were observed on the equatorial plate at metaphase I and chromosome fragments were detected at anaphase I.These results indicate that the increase of recombination frequency in Osfancm is dependent on OsMUS81.It is also suggested that the mutation in OsFANCM is likely result in an increase in the number of class ? COs.Osfancm is the first gene in food crops that has been shown to significantly increase recombination frequency.We hope to improve the frequency of recombination in food crops and improve breeding efficiency to provide better countermeasures through the genetic manipulation of the OsFANCM.