Evaluating the role of the Ralstonia solanacearum GspC protein in type II secretion substrate specificity.
H. TSENG (1), T. P. Denny (1) (1) University of Georgia, Athens, GA, USA.
Phytopathology 99:S130.

Abstract: The type II secretion (T2S) system in Ralstonia solanacearum secrets multiple plant cell wall-degrading enzymes and other proteins important for pathogenesis. GspC is an essential component of the T2S system, and is one of two proteins thought to help determine substrate specificity. The N-terminal half of GspC is conserved, but the C-terminal half usually has one of three protein-protein interaction domains. However, in R. solanacearum GspC lacks a predicted C-terminal protein-protein interaction domain, and this may contribute to its secreting more proteins than other bacteria. To investigate the role of GspC in the T2S system, we deleted gspC in R. solanacearum and tested various plasmid-borne genes for their ability to restore secretion of polygalacturonase and endoglucanase enzymes. The wild type and a C-terminally truncated form of R. solanacearum GspC, and wild-type Cupriavidus metallidurans GspC restored secretion of both enzymes almost to wild type levels. However, wild-type Burkholderia thailandensis GspC, which naturally lacks a C-terminal domain, partially restored secretion of polygalacturonase but did not restore secretion of endoglucanase. These results suggest that general recognition of secreted proteins by the R. solanacearum T2S system lies in both the secreted protein and GspC recognition. These insights could have broad ramifications, because the T2S system is a critical function for many plant and animal pathogens.