Single Gametophyte Sequencing Dissects Sex Difference Of Meiotic Crossover In Maize

Meiotic crossover(CO)plays a key role in producing gametophytes and generating genetic variation,which is the drive force of evolution and the base of genetic improvement.The patterns of CO production differ inter-and intra-species,as well as between sexes.However,sex-specific patterns of CO production were rarely profiled in plants.With the development of single cell sequencing technology,the CO patterns can be profiled in single gametophytes,providing the opportunity to study sex-specific CO patterns at single cell level.In this study,we constructed the first female recombination map at single cell level in plants,and compared with the male recombination map under same background,then analyzed the sex differences in CO frequency,distribution and interference.This research provides insights toward understanding the molecular mechanism of CO production between sexes and revealed that paternal selection can help to improve breeding efficiency.The major results are:1.We developed a method to isolate antipodal cells from single embryo sac for genomes sequencing in maize.Under ~1.2× sequencing depth,~40% genome coverage was obtained.Based on the 2,033,416 high-quality SNPs(Single Nucleotide Polymorphisms)in single female gametophyte population,a high-resolution female recombination map was constructed.Comparing with male,the female meiosis generates less COs,which consists with Arabidopsis,but not human and mouse,revealing that the sex difference in meiosis is species-specific.The female and male CO number are both positively correlated with longitudinal chromosome axis in male meiosis,indicating the sex-specific CO frequency is determined by synaptonemal complex(SC)length.2.COs from both sexes tend to occur in peri-telomere and are suppressed in peri-centromere.It was observed that the COs concentrate in translation start sites and translation terminal sites of genes for both sexes.In female and male,71 and 112 hot regions contained 755 and 1190 COs,respectively,which suggests that the dramatic difference in CO frequency between sexes was positively correlated by the differing number of hot regions.3.Based on Beam-Film(BF)model and gamma model,we found that the higher CO interference strength and lower class II CO amounts in female than in male,which is also supported by data from another genetic background.CO maturation inefficiency(CMI)is detected in some genetic backgrounds,suggesting that CMI in maize is determined by genetic elements but not sex,therefore maize may be an ideal model for dissecting CMI.In summary,the more designated class I and II COs are identified in male than in female based on BF model,accounting for the sex-specific CO frequency in maize.