A grant has been awarded to Drs. Amy Charkowski, Nicole Perna, and Ching-Hong Yang at the University of Wisconsin and Jeffery Dangl and Sarah Grant at the University of North Carolina to examine the expression, genetic diversity and evolution of the suites of virulence genes present in different strains of an important plant pathogenic bacterium. This bacterium, Erwinia carotovora, causes devastating "wilt" or "soft rot" diseases of important crops, including potato and its wild relatives. The wild host plants come from diverse environments around the world, particularly in the Andes region of South America, which is the ancestral home of potato.
This project will foster collaborations among a multidisciplinary group of scientists from five institutions in three countries. It will result in the training of student and postdoctoral researchers in each laboratory. It will also increase the capabilities of the laboratory facilities at one of the largest field research stations in Wisconsin, thus allowing modern molecular biology experiments to be performed on field samples near the research sites.
Even though E. carotovora is strictly a plant pathogen, it shares many virulence genes with important animal pathogens that cause diseases ranging from gastrointestinal illness to the plague. The results from this work will therefore provide information applicable to many diseases. This project will focus on a crucial common virulence system. This virulence system uses a "molecular syringe" to deliver bacterial proteins called effectors directly into animal or plant host cells. Once inside, the effector proteins manipulate the host cells to suppress disease defenses and promote bacterial growth. Nearly all studies of this key protein delivery system have been limited to laboratory settings. This project will bring studies from the laboratory to the field in order to understand the effects of the natural environment on the expression and function of these crucial virulence genes in a variety of plant hosts.
Genes encoding effector proteins vary tremendously, even within the same species. Thus the first goal of this project will be to identify as many of the E. carotovora effector proteins as possible using a new high throughput system. The investigators will then determine which of these effectors are produced in bacteria found on diseased plants in a variety of natural locations that differ in their ecology. Preliminary results indicate that field plants are typically infected with multiple strains of E. carotovora. In contrast, laboratory studies typically involve infecting a each plant with only one strain. By identifying the effectors present in each individual strain from naturally-infected plants, it will be possible to determine whether the effectors work in combination to promote growth of multiple strains.
To quantify the contribution that the effector genes make to bacterial growth and survival in the natural environment, E. carotovora mutants will be examined on diverse plants under natural conditions. Finally, wild plant species will be examined to determine if they have disease resistance genes that recognize specific E. carotovora effector proteins, and protect the plants from disease. The combined results from these experiments will be among the first tests of the presence, expression, effects and diversity of bacterial virulence genes under natural conditions. The gene sequence and expression data from these experiments will be deposited in ASAP (https://asap.ahabs.wisc.edu/annotation/php/ASAP1.htm), a publicly-available searchable web-based database.
