Isolation of NBS-LRR RGAs from invasive Wedelia trilobata and the calculation of evolutionary rates to understand bioinvasion from a molecular evolution perspective

• TIR (WTRGA1 and WTRGA2) and non-TIR (WTRGA3) NBS-LRR RGAs were isolated from the invasive Wedelia trilobata plant.
• The average dN/dS of TIR NBS-LRR R-genes/RGAs in invasive plants was significantly greater than that of non-invasive plants.
• These results provide the first preliminary molecular evidence supporting the natural enemy release hypothesis.

Supports for the molecular evolution of host–pathogen interactions on enemy release hypothesis are rare. According to the theory of plant immunity and the coevolution of hosts and pathogens, we hypothesized that the evolutionary rate (dN/dS) of resistance genes (R-genes) in invasive plants would be greater than in non-invasive plants, assuming that based on the enemy release hypothesis, the former would suffer less selection stress from co-evolutionary specialist pathogens. To test our hypothesis, we isolated and analyzed the conserved nucleotide-binding sites (NBS) of resistance gene analogues (RGAs) of an invasive weed, Wedelia trilobata (WTRGA). We then used the information in GenBank to compare the dN/dS of the NBS R-gene/RGAs in invasive and homologous non-invasive plants. Three W. trilobata NBS RGA sequences were obtained, belonging to the Toll/Interleukin-1 receptor (TIR) (WTRGA1 and WTRGA2) and non-TIR subclasses (WTRGA3). Compared with the homologous non-invasive plants, the invasive plants showed a significantly greater dN/dS for TIR NBS R-gene/RGAs (p < 0.0001), supporting our hypothesis. Future research should include an examination of R-genes/RGAs from more invasive plants on a population level to understand diversity and R-gene functions in invasive plant species, as well as to explore how disease resistance allows plants to adapt to changing pathogen stresses.