Untangle the knot: Soybean MLH1 in meiotic recombination

Climate change and global food demand require sustainable efforts to improve crop productivity and yields.The classical plant breeding approach harnesses the advantages of meiotic recombination or crossing over (CO) for crop development and trait improvement.During meiotic recombination, homologous chromosomes exchange genetic segments through pairing, synapsis, and recombination, thereby to generate genetic diversity.Several CO protein complexes and families like ZMM complex (Zipper 1-4, Mut S homolog 4-5, and meiotic recombination 3), MutLγ protein family (MLH1 and MLH3), and others ensure the error-free meiosis and uniform chromosome distribution in daughter cells without genetic anomalies (Wang and Copenhaver, 2018) (Figure 1A).Genetic COs are tightly regulated by two pathways.The first is class I interference-sensitive, which is controlled by the ZMM and MutLγ protein family and regulates 85 %-90 % of COs (Jackson et al., 2006).The remaining COs are governed by a class II interference-insensitive pathway, which is directed by MUS81 and FANCD2 (Kurzbauer et al., 2018).Because genetic recombination is key to diversity in nature, how proteins regulate COs is an active question in yeast, humans, and plants and understanding it can be particularly beneficial for enhancing breeding of crop plants ( Keeney et al., 1997;Wang and Copenhaver, 2018).In this issue of Plant Physiology, Wu et al. ( 2024) targeted soybean, an economically valuable crop that is highly desirable for oil and protein content, and investigated the role of GmMLH1, a homologue of MutLy-protein family, during meiotic recombination (Wu et al., 2024).Expanding on their previous work on EMS mutagenized soybean cultivar Williams 82, the authors identified a mutant line with fertility defects in both male and female gametes, which they named Gmfms1 (Glycine max female and male sterility 1) (Feng et al., 2019).With experimental validation that Gmfms1 has abnormal gamete phenotypes, the authors sought out the responsible causative gene.They crossed the Gmfms1 mutant with an elite Chinese soybean cultivar, Hedou 12 and observed a 3:1 segregation ratio in F 2 generation.The finding confirmed that a single recessive gene is responsible for the mutant phenotype in Gmfms1.To identify the responsible gene, Wu et al., (2024) selected the F 2 plants with less than two seeds/plant and performed bulked segregant analysis sequencing (BSA-seq).The sequenced mutants were mapped and compared against the wild type, which helped to identify a single nucleotide mutation in Glyma.04G254900.Moreover, Glyma.04G25490 was found to be similar to Arabidopsis MLH1(AtMLH1), and hence labeled as GmMLH1 in the present study.To determine whether GmMLH1 has a universal role across soybean cultivars, the authors knocked