This is a research planning grant for women. To be able to understand functions in pathogens and plants so that plant diseases can be controlled and cellular mechanisms for signal recognition between organisms can be deciphered, we will investigate enhancement of bacterial virulence functions by oligosaccharides. This enhancement will serve as a model system supporting further pursuit of virulence functions in fungi. Previous work has shown that plant cell walls contain a polygalacturonase inhibitor protein (PGIP) that recognizes and inhibits fungal polygalacturonases (PG) and that the association of PG and PGIP results in reduced breakdown of pectin so that oligosaccharides three to twenty units long are formed. These oligosaccharides have been shown to be inducers of defense responses in the plant cells and in Agrobacteria similar oligosaccharides have been suggested to be potent enhancers of virulence induction by plant phenolics. This research assesses the inhibition of bacterial PGs by pear and tomato PGIPs and determines the susceptibility to Agrobacteria infection of transgenic tomato plants expressing elevated amounts of PGIP. Furthermore, oligosaccharides optional for the enhancement of bacterialvirulence gene expression will be identified. The results from the studies outlined in this grant will provide the basis for the search in fungi for homologues to bacterial genes responsible for the regulation of virulence induction and enhancement. To be able to understand the signals that are exchanged between a microbial pathogen and a plant cell during infection, we will analyze the effect that sugar polymers have on the functions in a bacteria that allow it to infect the plant cells. These sugar polymers are known to be formed when a protein in the wall of the plant cell, PGIP, encounters an enzyme, PG, that fungi deploy in order to reach the interior of the plant cell being infected. The sugar polymers are known to trigger responses in plant cells that can slow the infection process, but they also have been suggested to enhance the infection functions in bacterial plant pathogens. Since little is known about the control of functions that fungal plant pathogenes need in order to infect plants, we will first describe the effects of the sugar polymers in the infection process by bacterial pathogens and then look for similar functions in the more complex fungal infections. We need to understand functions in both types of pathogens and in the plants in order to exercise control over plant diseases caused by these pathogens and in order to decipher basic mechanisms of communication between organisms.
