Pistia stratiotes (water lettuce) is a free-floating macrophyte that is capable of rapid vegetative propagation. The morphological structure of P. stratiotes has caused it to be one of the most notorious weeds causing severe impact on the environment and economy of infested areas. However, genomic studies on invasive aquatic plants are still limited and their molecular mechanism underlying of quick invasion are not well understood.
To fundamentally resolve the mechanism of its rapid invasion, researchers from Wuhan Botanical Garden sequenced and de novo assembled the P. stratiotes genome using short-read sequencing, PacBio sequencing and Hi-C technologies.
Results showed that the assembled genome was 311.87 Mb in size with an N50 value of 1.08 Mb. A total of 299.49 Mb (96.03%) were anchored to the 14 pseudochromosomes. By collinearity analysis, the four-fold synonymous third-codon transversion site (4DTv) and the synonymous substitution rate (Ks) distributions, two whole-genome duplication (WGD) events were identified in P. stratiotes, which were shared with S. polyrhiza and C. esculenta.
In addition, based on evolutionary analysis of gene families, they found gene families of P. stratiotes associated with disease resistance had undergone expansion, which might underly the species’ invasiveness. Also, a total of 85 NBS-LRR genes (disease-resistance gene family) were identified and functionally predicted in P. stratiotes in this study. Further, they revealed that tandem duplication events were likely to contribute to the recent expansion of the NBS-LRR gene family in P. stratiotes. This could be a vital reason for its invasion.
In conclusion, this research provides some new insights into the evolution of the invasive aquatic plant P. stratiotes, and it will constitute a value resource for genetic, ecological, and evolutionary studies in the family Araceae.
Characteristics of P. stratiotes genome (upper), and loss and gain events of NBS-LRR genes in eight species (below) (Image by WBG)
