OsMLH1 interacts with OsMLH3 to regulate synapsis and interference-sensitive crossover formation during meiosis in rice

Meiotic recombination is essential for reciprocal exchange of genetic information between homologous chromosomes and their subsequent proper segregation in sexually reproducing organisms. MLH1 and MLH3 belong to meiosis-specific members of the MutL-homolog family, which are required for normal level of crossovers (COs) in some eukaryotes. However, their functions in plants need to be further elucidated. Here, we report the identification of OsMLH1 and reveal its functions during meiosis in rice. Using CRISPR-Cas9 approach, two independent mutants, Osmlh1-1 and Osmlh1-2, are generated and exhibited significantly reduced male fertility. In Osmlh1-1, the clearance of PAIR2 is delayed and partial ZEP1 proteins are not loaded into the chromosomes, which might be due to the deficient in resolution of interlocks at late zygotene. Thus, OsMLH1 is required for the assembly of synapsis complex. In Osmlh1-1, CO number is dropped by similar to 53% and the distribution of residual COs is consistent with predicted Poisson distribution, indicating that OsMLH1 is essential for the formation of interference-sensitive COs (class I COs). OsMLH1 interacts with OsMLH3 through their C-terminal domains. Mutation in OsMLH3 also affects the pollen fertility. Thus, our experiments reveal that the conserved heterodimer MutL gamma (OsMLH1-OsMLH3) is essential for the formation of class I COs in rice. Copyright (C) 2021, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, and Genetics Society of China. Published by Elsevier Limited and Science Press. All rights reserved.

Automated summary

Meiotic recombination is essential for genetic exchange in sexually reproducing organisms. OsMLH1 is crucial for male fertility and crossover formation in rice, interacting with OsMLH3. The assembly of synapsis complex relies on OsMLH1.