Near chromosome level genome assembly of the fruit pest Drosophila suzukii using long read sequencing
Over the past decade, the spotted wing Drosophila, Drosophila suzukii, has invaded Europe and America and has become a major agricultural pest in these areas, thereby prompting intense research activities to better understand its biology. Two draft genome assemblies based on short read sequencing were released in 2013 for this species. Although valuable, these resources contain pervasive assembly errors and are highly fragmented, two features limiting their values. Our purpose here was to improve the assembly of the D. suzukii genome. For this, we generated PacBio long read sequencing data at 160X sequence coverage and assembled a novel, contiguous D. suzukii genome. We obtained a high quality assembly of 270 Mb (with 546 contigs, a N50 of 2.6Mb, a L50 of 15, and a BUSCO score of 95% that we called WT3 2.0. We found that despite 16 rounds of full sib crossings the D. suzukii strain that we sequenced has maintained high levels of polymorphism in some regions of its genome (ca. 19Mb) As a consequence, the quality of the assembly of these regions was reduced. We explored possible origins of this high residual diversity, including the presence of structural variants and a possible heterogeneous admixture pattern of North American and Asian ancestry. Overall, our WT3 2.0 assembly provides a higher quality genomic resource compared to the previous one in terms of general assembly statistics, sequence quality and gene annotation. This new D. suzukii genome assembly is therefore an improved resource for high throughput sequencing approaches, as well as manipulative genetic technologies to study D. suzukii.