KOSEN 한인과학기술자네트워크

Meiosis is a specialized cell division and is fundamental to gametogenesis of sexually reproducing organisms. During meiosis, meiotic recombination ensures genome integrity and increases genetic diversity in population. Meiotic recombination is initiated by programmed DNA double-strand breaks (DSBs) formation. The repair of DSBs leads to reciprocal crossovers or non-crossovers (gene conversions) via different DNA repair pathways. DSBs outnumber crossovers, thus only a few of DSBs are eventually repaired to crossovers. Anti-recombination factors restrict crossover number while crossover interference causes even spaced crossover pattern by preventing coincidence of crossovers in the same pair of chromosomes. Intriguingly the DSBs and crossovers are non-uniform along chromosomes, typically occurring at narrow regions, called recombination hotspots. Plant meiotic recombination hotspots occur at gene promoters and terminators in euchromatin while heterochromatin is suppressed, indicating that chromatin structure influences recombination distribution (Choi et al., 2013 Nature genetics). Notably, meiotic recombination process also requires dynamic assembly and disassembly of meiotic protein complexes in time and space. 

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We aim to understand mechanistically how plant meiotic recombination is controlled by the interplay between meiotic proteins, chromatin and higher order of chromosome structure. To achieve this, we apply advanced methods of recombination measurements at different scales from single base-pair to genome (SPO11-oligonucleotide seq, pollen typing, fluorescent reporter systems, genotyping-by-sequencing). Two key approaches are a genome-wide mapping of SPO11-oligonucleotides to determine meiotic DSBs sites in plants, and a forward genetic screen of crossover rate mutants via high-throughput fluorescent seed-scoring and tetrad analysis in Arabidopsis. We developed DeepTetrad, a deep learning-based image recognition package for pollen tetrad analysis that enables high-throughput measurements of crossover frequency and interference in individual plants

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More importantly, our studies on meiotic recombination can help accelerate plant breeding for crop improvement by recombining or mapping useful genetic variations that occur spontaneously or by a result of mutagen in wild type plant accessions at particular areas and diverse domesticated varieties. New combinations of DNA variations contributing to crop productivity, disease resistance, fruit and grain quality can be generated by increasing crossover frequency between tightly linked alleles which had been hardly recombined along a chromosome. As soon as the useful DNA variations are identified by genetic mapping via increasing crossovers, a CRISPR/Cas9 system can be also applied to edit plant genomes of current varieties.