Mechanism Of RAD51 And ASAP1 In Plant Meiosis

Meiosis is very important for sexual reproduction and genetic diversity in eukaryotes.Evolutionarily conserved genes RAD51 and DMC1 have important role in homologous recombination during meiosis.Previous studies found that though both RAD51 and DMC1 have recombinase activity,the recombinase activity of RDA51 is not necessary during meiosis.RAD51 may plays a supporting role.But how RAD51 plays a supporting role in meiosis is still unknown.SMC5/6 complex is highly conserved in eukaryotes,mainly involved in DNA damage repair.Recent studies found that ASAP1 is a missing subunit of SMC5/6 complex in Arabidopsis.We found that mutant ASAP1 can suppress the sterility phenotype of rad51.The fertility of asapl rad51 double mutant is approximately 48%of the wild type.Further research found that asapl rad51 dmcl triple mutant is completely sterile,indicating that DMC1 genetic epistasis of RAD51 and ASAP1.In rad51 mutant,since DNA double strand breaks(DSB)can not be repaired during meiosis,chromosome highly fragmented.Consistent with the fertility phenotype,we found that the degree of the chromosome fragmentation in asapl rad51 double mutant declined significantly,while the rad51 asapl dmcl triple mutant is the same as the rad51 single mutant.We also found that DMC1 and RAD51 can interact with the ASAP1.Based on these results,we believe that the role of RAD51 is inhibiting ASAP1 to disarm ASAP1's inhibition on DMC1.In rad51 single mutants,since ASAP1 can not be suppressed,thereby DMC1 is inhibited by ASAP1,DSB can not be repaired during meiosis.In asapl rad51 double mutants,the inhibition of ASAP 1 on DMC1 is released,DMC1 can exercise the function of DSB repair,so the plant is fertile.The asapl rad51 dmcl triple mutant,due to lack of DMC1,DSB can not be repaired,so the plant is infertile.Our new study reveals the function of RAD51 in meiosis and discovered a new mechanism in plant meiosis.