On February 15th, the team of Professor Yan Jianbing from HZAU published a paper entitled “Single Gametophyte Sequencing Reveals that Crossover Events Differ between Sexes in Maize” on Nature Communications, revealing the similarities and differences of recombination frequencies between male and female gametes in maize. This study developed a method to isolate single female gametophyte for further genomes sequencing in maize. Combining the previously published microspore genome data of the same genetic material, the Beam Film model was used to deeply analyze differences in CO(Crossover) formation between sexes, and the phenomenon of CO Maturation Inefficiency (CMI) was detected. The study found that in the same genetic background, male gametes (19.3 per microspores) undergo more crossover than female gametes (12.4 per embryo sac).
Crossover or CO is an important step to ensure the equal separation of homologous chromosomes in meiosis. It also provides a large number of genetic variations for sexual reproduction organisms, which are the basis of species evolution. There are differences in the frequency of CO occurrence, distribution and interference on chromosomes in inter- and intra-species. Moreover, there may be differences in CO formation between different sexes of the same species. Previously, based on mammalian or human studies, because of the large differences in genetic background, this sex difference cannot exclude the influence of genetic background. In the study of plants (Arabidopsis thaliana), due to the limitations of technical conditions, the differences between male and female are not deeply analyzed.
The author further used mathematical models to reveal why crossover events differ between sexes in maize. The data of meiotic crossover between sexes were simulated by using Beam Film model and Gamma model. The results showed that in the process of meiotic crossover, female had stronger CO interference and less non-interference type (type II) CO than male. In 2018, a research team of Cornell University concluded that there is not many differences in the formation of CO in the meiosis of maize, but after the data was simulated by the Beam Film model, it was found that female had stronger CO interference and less non-interfering CO, which explained why female CO is less than male CO under the same genetic background and environmental conditions.
In addition, through the Beam Film model, it was further found that there were CMI in both male and female meiosis in the genetic background of maize KYS and B73 x Mo17, but not in the genetic background of SK x Zheng58. In recent years, CMI has been proved to be an important event in the process of meiotic recombination. CMI may cause human Down’s syndrome and abortion of young male mice. It is very difficult to study the genetic basis and molecular mechanism of CMI in mammals. The results of this study suggested that maize may be an ideal model material for studying CMI, which will lay the foundation for us to understand the molecular mechanism of recombination. This study has also greatly changed our understanding of the occurrence of meiotic crossover, and has an important impact on cross-breeding of crops, which means that the frequency of recombination events generated by the same hybrid combination is different.
The research was funded by the National Natural Science Foundation of China, the National Key Laboratory of Crop Genetic Improvement, and the Huazhong Agricultural University Scientific & Technological Self-Innovation Foundation. Master-degree candidate Luo Cheng and post doctorate Li Xiang are the co-first authors of the article; and Dr. Li Xiang and Professor Yan Jianbing are co-corresponding authors. Luo Cheng is a graduate student of the College of Life Science and Technology since 2017; Dr. Li Xiang is in the list of the 2017 National Postdoctoral Innovation Talent Support Program. For the first time, Li Xiang achieved single-cell sequencing in plants and completed a series of studies on single-cell sequencing of plants. He analyzed three scientific issues—the rule of crossover(Li et al, Nature Communications, 2015; Luo et Al, Nature Communications, 2019), reprogramming of chromosomes during sexual reproduction (Liet al, Molecular Plant, 2019), and mechanisms of maize haploid induction (Li et al, Nature Communications, 2017; Liu et al, Molecular Plant, 2017).
