Dwivedi, M.; Vijay, N.

Review of Christenhusz et al., Wellcome Open Research. A high-quality genome sequence of the Annual Mercury, Mercurialis annua is generated as part of the Darwin Tree of Life Project. The Annual Mercury plant is a good study system for evolutionary transitions between sexual systems, mechanisms of sex determination in plants and changes in ploidy level. The XX female sequenced in this study provides a chromosome-level assembly with reasonable contiguity and high gene completeness. We compare the gene completeness of the assembly presented with those of closely related species, including another published assembly of the Annual Mercury generated using a polyploid individual. Annotation and comparative analysis of the organelle genomes suggest complete circular assemblies. However, we note that the NCBI submissions are tagged as linear. The repeat content identified on the autosomes and X chromosome appears comparable, suggesting the sex chromosomes are relatively recent. An alternative possibility is that our preliminary analysis failed to identify repeats unique to the X chromosome or that these repeat regions have not been assembled in the genome. The harder-to-assemble centromere and telomere regions are not annotated in the genome and are potentially incomplete or missing. We identify putative centromere regions with elevated GC content, but they must be validated. The demographic histories reconstructed for the autosomes and X suggest distinct trajectories irrespective of the scaling parameters. Compared to the autosomes, the older histories recorded on the X are a promising avenue for further work to study the origin of the sex chromosome. Our preliminary assessment of the genome sequence suggests the genome is of sufficiently good quality for use as a reference for diverse analysis aimed at answering important eco-evolutionary questions of interest that can be answered using this system.