Ian is Professor of Genetics and Epigenetics at the University of Cambridge, where he leads a group in the Department of Plant Sciences. The Henderson group investigate plant genomes, recombination, and meiosis using the model plant Arabidopsis thaliana and crop species including tomato and wheat. The group has recently been heavily using nanopore sequencing to assemble highly repetitive parts of the Arabidopsis genome, including the centromeres, and studying their genetic and epigenetic regulation.

Centromeres attach chromosomes to spindle microtubules during cell division and, despite this conserved role, show paradoxically rapid evolution and are typified by complex repeats. We have used nanopore sequencing to generate complete assemblies of the centromeres of the model plant Arabidopsis thaliana. The centromeres consist of megabase-scale tandemly repeated satellite arrays, which support loading of the centromere-specific histone variant CENH3. Nanopore sequencing has also allowed us to generate high-resolution maps of DNA methylation within the centromeres for the first time. Our assembly has revealed that satellite variants exist that are private to each chromosome and that CENH3 preferentially occupies satellites that show least divergence and occur in higher-order repeats. The centromeres are also invaded by ATHILA retrotransposons, which disrupt genetic and epigenetic organization. We propose that Arabidopsis centromeres are evolving via cycles of satellite homogenization and retrotransposon-driven diversification.