Understanding the architecture and biology of the type II protein secretion system in plant-pathogenic Xanthomonas bacteria

Abstract

Virulence of Gram-negative plant-pathogenic Xanthomonas bacteria depends on protein secretion systems, such as the type II and type III secretion (T2S/T3S) systems. Focus of this study is the architecture of the Xps-T2S system and its role in infection. Structural modelling, fluorescence microscopy, in vitro and in vivo protein interaction studies revealed three independently assembling subcomplexes of the T2S system: the XpsD secretin channel, an inner membrane XpsCLM assembly platform complex and an XpsF-XpsIJK complex which connects the pseudopilus with an assembly platform component. These preformed XpsCLM and XpsF-IJK subcomplexes presumably bind to the XpsD secretin channel and form a scaffold for the oligomerization of the hexameric ATPase XpsE in the cytoplasm. Novel T2S substrates were identified in planta including proteases and cell wall degrading enzymes and growth experiments shed light on the role of T2S in nutrient acquisition of Xanthomonas during infection.