Transformation of Phytophthora capsici with genes for green and red fluorescent protein for use in visualizing plant-pathogen interactions

One of many uses of fluorescent proteins in plant pathology is their constitutive expression in a pathogen in order to facilitate microscopic visualization of host-pathogen interactions. However, if such transformants are to be useful, it is important that they be similar to wild type isolates in their ability to cause disease. The vegetable pathogen Phytophthora capsici was transformed to stably and constitutively express genes for either a green (pgfp) or red (tdTomato) fluorescent protein. All transformants fluoresced in all life stages, but varied in their intensity and contained one, two, or five copies of pgfp or tdTomato, as determined by Southern analysis. One transformant labeled with green fluorescent protein had reduced growth on artificial medium, produced smaller lesions on detached pepper fruit, and was reduced in virulence on pepper seedlings, compared to the wild type isolate. For these reasons, it is unsuitable for use in studies of host-pathogen interactions. Based on their intense fluorescence and similarity to the wild type isolate in growth and virulence, the other four transformants will be useful in future microscopy studies of interactions between P. capsici and its various hosts.