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1. Genetic and environmental influences on the distributions of three chromosomal drive haplotypes in maize

   Brady, MJ; Dawe, RK (July 2025, PLOS genetics)

   Meiotic drive elements are regions of the genome that are transmitted to progeny at frequencies that exceed Mendelian expectations, often to the detriment of the organism. In maize there are three prevalent chromosomal drive elements known as Abnormal chromosome 10 (Ab10), K10L2, and the B chromosome. There has been much speculation about how these drivers might interact with each other and the environment in traditional maize landraces and their teosinte ancestors. Here we used genotype-by-sequencing data to score more than 10,000 maize and teosinte lines for the presence or absence of each driver. Fewer than ~0.5% of modern inbred lines carry chromosomal drivers. In contrast, among individuals from 5331 open-pollinated landraces, 6.32% carried Ab10, 5.16% carried K10L2, and 12.28% carried at least one B chromosome. These frequencies are consistent with those reported in previous studies. Using a GWAS approach we identified unlinked loci that associate with the presence or absence of the selfish genetic elements. Many significant SNPs are positively associated with the drivers, suggesting that there may have been selection for alleles that ameliorate their negative fitness consequences. We then assessed the contributions of population structure, associated loci, and the environment on the distribution of each chromosomal driver. There was no significant relationship between any chromosomal driver and altitude, contrary to conclusions based on smaller studies. Our data suggest that the distribution of the major chromosomal drivers is primarily influenced by neutral processes and the deleterious fitness consequences of the drivers themselves. While each driver has a unique relationship to genetic background and the environment, they are largely unconstrained by either. 

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2. The maize striate leaves2 ( sr2 ) gene encodes a conserved DUF3732 domain and is homologous to the rice yss1 gene

   https://doi.org/10.1002/pld3.567  

   Brady, Meghan J; Cheam, Maya; Gent, Jonathan I; Dawe, R Kelly (February 2024, Plant Direct)

   Abstract Maize striate leaves2(sr2) is a mutant that causes white stripes on leaves that has been used in mapping studies for decades though the underlying gene has not been identified. Thesr2locus has been previously mapped to small regions of normal chromosome 10 (N10) and a rearranged variant called abnormal chromosome 10 (Ab10). A comparison of assembled genomes carrying N10 and Ab10 revealed only five candidatesr2genes. Analysis of a stock carrying thesr2reference allele (sr2‐ref) showed that one of the five genes has a transposon insertion that disrupts its protein sequence and has a severe reduction in mRNA. An independent Mutator transposon insertion in the gene (sr2‐Mu) failed to complement thesr2‐refmutation, and plants homozygous forsr2‐Mushowed white striped leaf margins. Thesr2gene encodes a DUF3732 protein with strong homology to a rice gene with a similar mutant phenotype calledyoung seedling stripe1(yss1). These and other published data suggest thatsr2may have a function in plastid gene expression. 

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3. The Role of Meiotic Drive in Chromosome Number Disparity Between Heterosporous and Homosporous Plants

   https://doi.org/10.1111/mec.17757  

   Kinosian, Sylvia P; Barker, Michael S (April 2025, Molecular Ecology)

   In vascular plants, heterosporous lineages typically have fewer chromosomes than homosporous lineages. The underlying mechanism causing this disparity has been debated for over half a century. Although reproductive mode has been identified as critical to these patterns, the symmetry of meiosis during sporogenesis has been overlooked as a potential cause of the difference in chromosome numbers. In most heterosporous plants, meiosis during megasporogenesis is asymmetric, meaning one of the four meiotic products survives to become the egg. Comparatively, meiosis is symmetric in homosporous megasporogenesis and all meiotic products survive. The symmetry of meiosis is important because asymmetric meiosis enables meiotic drive and associated genomic changes, while symmetric meiosis cannot lead to meiotic drive. Meiotic drive is a deviation from Mendelian inheritance where genetic elements are preferentially inherited by the surviving egg cell, and can profoundly impact chromosome (and genome) size, structure, and number. Here we review how meiotic drive impacts chromosome number evolution in heterosporous plants, how the lack of meiotic drive in homosporous plants impacts their genomes, and explore future approaches to understand the role of meiotic drive on chromosome number across land plants. 

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4. Helicase LSH/Hells regulates kinetochore function, histone H3/Thr3 phosphorylation and centromere transcription during oocyte meiosis

   https://doi.org/10.1038/s41467-020-18009-3  

   Baumann, Claudia; Ma, Wei; Wang, Xiaotian; Kandasamy, Muthugapatti K.; Viveiros, Maria M.; De La Fuente, Rabindranath (December 2020, Nature Communications)

   null (Ed.)

   Abstract Centromeres are epigenetically determined nuclear domains strictly required for chromosome segregation and genome stability. However, the mechanisms regulating centromere and kinetochore chromatin modifications are not known. Here, we demonstrate that LSH is enriched at meiotic kinetochores and its targeted deletion induces centromere instability and abnormal chromosome segregation. Superresolution chromatin analysis resolves LSH at the inner centromere and kinetochores during oocyte meiosis. LSH knockout pachytene oocytes exhibit reduced HDAC2 and DNMT-1. Notably, mutant oocytes show a striking increase in histone H3 phosphorylation at threonine 3 (H3T3ph) and accumulation of major satellite transcripts in both prophase-I and metaphase-I chromosomes. Moreover, knockout oocytes exhibit centromere fusions, ectopic kinetochore formation and abnormal exchange of chromatin fibers between paired bivalents and asynapsed chromosomes. Our results indicate that loss of LSH affects the levels and chromosomal localization of H3T3ph and provide evidence that, by maintaining transcriptionally repressive heterochromatin, LSH may be essential to prevent deleterious meiotic recombination events at repetitive centromeric sequences. 

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5. Investigating Sk-3-based spore killing through DNA deletion in Neurospora crassa

   https://doi.org/10.30707/1734473255.348925  

   Krivograd, Sophie (January 2024, ISU ReD: Research and eData)

   Meiotic drive describes a process in which selfish alleles are recovered in more than half of a progeny generation. It is a type of gene drive and it has been discovered in strains of Neurospora, a filamentous fungus, through its spore killing mechanism. One of the most studied meiotic drive elements within N. crassa is Spore killer-3 (Sk-3). Previous studies have indicated that there is a genomic region within Sk-3 that encodes resistance to spore killing and another that encodes an element that is required for spore killing. Sk-3’s resistance gene, rsk, has been identified. However, the exact region that mediates Sk-3’s spore killing mechanism is currently unknown. In a previous study, it was found that a mutation called rfk-2UV disrupts spore killing by Sk-3. To better understand the region of Chromosome III in which rfk-2UV is located (its exact location is unknown), I constructed a deletion vector to replace a DNA interval (v374) with a hygromycin resistance gene marker (hph). Transformants were crossed to produce offspring, and offspring were tested to determine if they possess the ability to kill ascospores. These findings will contribute to future efforts to determine the molecular nature of rfk-2UV and why this mutation disrupts the ability of Sk-3 to kill spores. 

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