The chromosome-level genome of a free-floating aquatic weed Pistia stratiotes provides insights into its rapid invasion.

Pistia stratiotes (Araceae), commonly referred to as water lettuce, is one of the most notorious weeds that cause severe damage to the economy and natural ecosystems of infested areas. In order to explore the mechanism of its rapid invasion, here, we assembled a high-quality chromosome-level genome for P. stratiotes based on the Illumina sequencing, PacBio sequencing, and Hi-C scaffolding technology. The assembled genome is 311.87 Mb in size with a contig N50 of 1.08 Mb. The contigs were further anchored on 14 pseudochromosomes with a scaffold N50 of 21.21 Mb. A total of 20,356 protein-coding genes were predicted, of which 79.35% were functionally annotated here. Evolutionary analysis showed that P. stratiotes and Colocasia esculenta were clustered together as sister lineages that diverged approximately 61 Ma. The synteny analyses indicated that two whole-genome duplication (WGD) events occurred within a short period in P. stratiotes. Moreover, comparative genome analysis indicated that the expansion of gene families corresponding to disease resistance might contribute to rapid invasion in P. stratiotes. Also, we analysed the disease-resistance gene family (NBS-LRR) involved in plant defence. A genome-wide search in P. stratiotes genome identified 85 NBS-LRR genes in this study. In conclusion, this study provides some new insights into the evolution of the invasive aquatic plant P. stratiotes. Our reference genome will also provide valuable resources for future invasion genomic research programmes.