Spotting the Difference: Comparing the Genome of Corymbia with its Larger Cousin Eucalyptus grandis

Corymbia is a sister genus to Eucalyptus with C. citriodora (spotted gum) having a prominent role in forestry. In the past few decades it has been valued for timber, essential oil and energy production in the drier subtropical regions of Australia, China, India and Brazil. The Corymbia Genome Consortium is generating a high quality genome sequence anchored to a dense genetic map to underpin evolutionary studies, germplasm management and accelerated breeding by genomic technologies. We have generated initial assemblies and a dense genetic map to facilitate comparative genome studies, particularly with the larger reference Eucalyptus grandis genome. The resources we have developed will facilitate transfer of genomic resources between the taxa, and broaden our understanding of the evolutionary drivers of genome variation within the eucalypt group. The Corymbia genome (reported as 370 Mb) is ~40% smaller relative to E. grandis. We will report progress on our understanding of the basis of this difference in genome size within the eucalypts, where the base chromosome size of 11 is remarkably prevalent. More specifically, we will present statistics of de novo assembly efforts using Illumina short reads, PacBio long reads and hybrid approaches that combine data from the two platforms. We demonstrate that hybrid assembly strategies even with low coverage PacBio data have already enabled us to generate a  draft assembly of considerably improved quality for a complex genome. The Corymbia draft genome assembly will be released as an open-source platform and we are currently seeking additional partners.