Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/24/2002
Publication Date: N/A
Technical Abstract: Plant and animal pathogenic bacteria have evolved a specialized protein secretion system called type III to directly inject proteins into their host cells. The Type III secretion system (TTSS) plays an important role in plant-microbe interactions since mutation in TTSS causes a loss of bacterial pathogenicity. The TTSSs of both animal and plant pathogenic bacteria occur as large clusters comprising several genes that encode the secretion apparatus as well as proteins that are secreted. The structural components of the secretion apparatus are highly conserved among bacterial pathogens. Recent studies have identified TTSSs in symbiotic bacteria including Sinorhizobium fredii USDA257, Rhizobium sp NGR234, Mesorhizobium loti MAF303099, and Bradyrhizobium japonicum USDA110. The TTSSs in symbiotic bacteria also occur in cluster of about 25 to 39 kb and contain several open-reading frames, some of which are highly homologous to ysc genes of Yersinia and hrc genes of plant bacterial pathogens. A few proteins located in the TTSSs of symbiotic bacteria such as NolX, NolB, and y4xL are secreted into the rhizosphere upon flavonoid induction. Type III secreted proteins appear to play an important role in regulating nodulation in a host-dependent manner. The secretion of some of the extracellular proteins appears to be facilitated by novel filamentous appendages that are produced by S. fredii USDA257 upon induction by flavonoids. Even though there has been no direct evidence for the type III secreted proteins being injected into the host cells, the association of NolX and few other secreted proteins on the filamentous appendages suggest that they may function as conduit for delivery of these proteins into the host cell.