Just add water: A simple floral bud injection method for stable Agrobacterium-mediated transformation in two ecotypes of Mimulus guttatus

Stable transformation is the biggest challenge for studying gene function in plants. In most plant species, stable transformation requires the development of arduous tissue culture and regeneration methods that often fail and can cause undesirable genetic changes. Floral transformation methods bypass these challenges by infiltrating Agrobacterium directly into the ovules of developing flowers. However, this method has had limited success outside of a handful of plant species and genotypes within those species. Here, we demonstrate that the floral infiltration method is effective for some, but not all genotypes of the yellow monkeyflower, Mimulus guttatus, a model system for studies of ecology and evolution. To conduct transformation in genotypes where infiltration failed, we developed a novel floral injection method. Beyond expanding the number of genotypes that can be transformed, the floral injection method has other advantages, such as allowing plants to be infiltrated multiple times and a reduction in floral abscission and male sterility. Through a combination of floral infiltration and injection methods, we were able to transform both coastal perennial and inland annual genotypes of M. guttatus, which sets the stage for understanding the molecular genetic underpinnings of local adaptation to the divergent habitats occupied by these distinctive ecotypes. Overall, the development of these efficient transformation methods will open up a wide range of new research avenues in the M. guttatus species complex.