Iwakami, S. | bioRxiv Science

bioRxiv2021

Gene expression shapes the patterns of parallel evolution of herbicide resistance in the agricultural weed Monochoria vaginalis

The evolution of herbicide resistance in weeds is an example of parallel evolution, through which genes encoding herbicide target proteins are repeatedly represented as evolutionary targets. The number of herbicide target-site genes differs among species, and little is known regarding the effects of duplicate gene copies on the evolution of herbicide resistance. We investigated the evolution of herbicide resistance in Monochoria vaginalis, which carries five copies of sulfonylurea target-site acetolactate synthase (ALS) genes. Suspected resistant populations collected across Japan were investigated for herbicide sensitivity and ALS gene sequences, followed by functional characterisation and ALS gene expression analysis. We identified over 60 resistant populations, all of which carried resistance-conferring amino acid substitutions exclusively in MvALS1 or MvALS3. All MvALS4 alleles carried a loss-of-function mutation. Although the enzymatic properties of ALS encoded by these genes were not markedly different, the expression of MvALS1 and MvALS3 was prominently higher among all ALS genes. The higher expression of MvALS1 and MvALS3 is the driving force of the biased representation of genes during the evolution of herbicide resistance in M. vaginalis. Our findings highlight that gene expression is a key factor in creating evolutionary hotspots.

plant biology↗

bioRxiv2020

Drastic shift in flowering phenology, an instant reproductive isolation mechanism, explains the population structure of Imperata cylindrica in Japan

Reproductive isolation plays an important role in population differentiation and speciation, thus enhancing biodiversity in wild plants. Hybridisation sometimes involves rapid reproductive isolation between parents and their hybrids through the novel traits of hybrids derived from a new combination of genomes. Here, we report how a hybrids new phenotype contributes to rapid reproductive isolation between two ecotypes of Imperata cylindrica. The two ecotypes differ in their flowering phenology and habitats. An analysis with genetic markers revealed that hybrid populations consisted of only F1 individuals. Both parental ecotypes flowered in spring, but F1s flowered in fall. This drastic shift in flowering phenology prevented backcrossing parental ecotypes to F1. F1s flowered in fall and dispersed seeds in winter. The germination percentage of seeds set on F1 was extremely low in their habitats, and seedlings did not survive due to the low temperatures in winter, resulting in the absence of a F2 generation. In conclusion, flowering phenology mismatch promotes reproductive isolation between parents and F1, resulting in a hybrid population consisting of only F1s.

evolutionary biology↗