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Department of Plant Sciences

Sex and disease - recombination hotspots in plant immunity genes

The Henderson group has published a new paper looking at the relationship between genetic recombination and genes important for immunity in the model plant Arabidopsis thaliana. The majority of plants, animals and fungi reproduce sexually, which has a profound effect on patterns of genetic diversity. For sexual reproduction to occur a specialized cell division called meiosis generates gametes (sex cells) with recombined DNA. During meiosis homologous chromosomes undergo reciprocal exchange of genetic material called crossover, which mixes parental sequences. Crossover frequency is highly variable along chromosomes and is typically concentrated in narrow regions called hotspots. Sexual reproduction is proposed to provide a major advantage during host-pathogen coevolution. This theory predicts that crossover hotspots will be associated with genes that play important roles in the immune system, where diversity may be beneficial. To investigate this idea, work in the paper mapped patterns of crossover frequency in relation to genes that plants use to recognize pathogens. It was observed that a subset of Arabidopsis thaliana resistance genes overlap with strong crossover hotspots. However, it was also observed that resistance genes could be coldspots, which correlated with chromosomal rearrangements between varietal lines (ecotypes). Using Arabidopsis ecotypes it is also shown that natural genetic variation has a strong modifying effect on resistance gene cluster recombination rates. Together this work shows complex variation in resistance gene crossover patterns, which may relate to heterogeneity in coevolutionary pressures experienced at different loci, in addition to the effects of structural genetic diversity.