D.L. Coplin, D.R. Majerczak, J.-H. Ham, D. Mackey
Pantoea stewartii subsp. stewartii (Pnss) causes Stewart's bacterial wilt and leaf blight, a serious disease of sweet corn and maize in the USA. The pathogenicity of Pnss depends on synthesis of extracellular polysaccharide and a Hrp type III secretion system. Since the regulation and genetics of both cps and hrp genes are very similar in Erwinia amylovora, Stewart's wilt has served as a comparative model system for fire blight. WtsE, a Hrp type III secreted effector protein, is essential for the virulence of Pnss on corn. It belongs to the AvrE-family of effectors, which includes DspE from E. amylovora. WtsE induced cell death in corn, tobacco, Nicotiana benthamiana and Arabidopsis, when it was transiently produced in plant cells following Agro-infiltration or translocated into plant cells from Pnss, Escherichia coli or Pseudomonas syringae pv. phaseolicola. In corn, WtsE-induced cell death was not inhibited by cycloheximide, unlike the HR induced by a known Avr-protein. In contrast, WtsE-induced cell death in tobacco and N. benthamiana appeared to be an HR. It has recently been shown that members of a family of type III effector proteins from animal pathogens mimic activated, small GTPases. This activity depends on both a WXXXE motif, which is conserved in the animal effector proteins and on a sub-cellular localization signal. We have found that all but one member of the AvrE-family of type III effectors contain one or two copies of the WXXXE motif and a predicted endoplasmic reticulum membrane retention signal (ERMRS). Site-directed mutagenesis of either the ERMRS or both copies of the WXXXE motif in WtsE dramatically reduced the ability of Pnss to cause disease in corn and nearly eliminated its ability to cause an HR in non-hosts. We therefore hypothesize that WtsE functions as a G-protein mimic.
Coplin, D.L., Majerczak, D.R., Ham, J.-H. and Mackey, D. (2008). THE WtsE VIRULENCE EFFECTOR FROM PANTOEA STEWARTII, A PLANT SIGNAL MIMIC?. Acta Hortic. 793, 203-212
DOI: 10.17660/ActaHortic.2008.793.28
Stewart's wilt, AvrE, DspE, HR, water-soaking

Acta Horticulturae