An improved chromosome-level genome assembly of perennial ryegrass (Lolium perenneL.)

This work is an update and extension of the previously published article “Ultralong Oxford Nanopore Reads Enable the Development of a Reference-Grade Perennial Ryegrass Genome Assembly”, by Frei et al.. The published genome assembly of the doubled haploid perennial ryegrass (Lolium perenneL.) genotype Kyuss marked a milestone for forage grass research and breeding. However, order and orientation errors may exist in the pseudo-chromosomes of Kyuss, since barley (Hordeum vulgareL.), which diverged 30 million years ago from perennial ryegrass, was used as the reference to scaffold Kyuss. To correct for structural errors possibly present in the published Kyuss assembly, wede novoassembled the genome again and generated 50-fold coverage high-throughput chromosome conformation capture (Hi-C) data to assist pseudo-chromosome construction. The resulting new chromosome-level assembly showed improved quality with high contiguity (contig N50 = 120 Mb), high completeness (total BUSCO score = 99%), high base-level accuracy (QV = 50) and correct pseudo-chromosome structure (validated by Hi-C contact map). This new assembly will serve as a better reference genome forLoliumspp. and greatly benefit the forage and turf grass research community.