An annotated draft genome of Lythrum salicaria (Purple loosestrife) to study rapid evolution and invasion genetics.

Background/Question/Methods

Invasive species spread rapidly displace native species, posing a threat to native ecosystems. The field of invasion genetics examines the genetic causes and consequences of biological invasions and how gene expression and plasticity evolve as invasive species adapt to new environments. Here, we present the de novo assembly and annotation of a genome for the perennial plant Lythrum salicaria (Lythraceae), which is widespread in Eurasia and invasive across North America. There is good evidence that L. salicaria has rapidly evolved differences in flowering time to adapt to differences in season length, facilitating its spread. We sequenced and assembled a genotype (IL-3-3-1) collected from Israel and confirmed as a diploid using flow cytometry. To annotate the genome and identify genes associated with flowering time variation, we sequenced mRNA from floral tissue (meristem + flowers + fruits + stems) from five early and five late flowering plants. These individuals were grown from seeds collected in the field (41.975/-75.196) and maintained in a large common garden field experiment located at Queen’s University Biological Station (QUBS).

Results/Conclusions

The draft genome assembly contains 648 sequences ranging from 1005bp to 160Mbp. We did two transcriptome assemblies, a de novo assembly (355878 transcripts) and one using the genome as a reference (79682 transcripts). From a differential expression (DE) analysis we found that 2466 transcripts are differentially expressed (padj < 0.05) between early and late flowering plants, some of those transcripts align to genes that control flowering in model species like Arabidopsis thaliana. We are using the transcriptome results to annotate the draft genome. Our draft assembly will enable molecular and functional genomic studies of L. salicaria to examine genetic mechanisms of invasion and rapid adaptation in novel environments.