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inly regulatory components, are lack ing. The gene content and order is highly conserved between E. pyrifoliae and E. tasmaniensis. A similar island was not found in E. billingiae. However, it remains unclear, if this T3SS is operative because UNC2250 of the incom pleteness in comparison to the SPI 1 and the replaced genes. Recent results from pathogenicity tests on imma ture pears with SPI 1 like mutants of E. amylovora indi cate that it is not essential UNC2250 for pathogenicity, Even for Salmonella typhimurium it was shown, that only the ini tial infection stages are affected in mutants while they remain pathogenic when applied by different routes, Only few CDS for putative effector proteins could be identified in the erwinias. Most of those proteins are thought to affect or to be secreted by the T3SS.

The sug gested effector SrfC of Pectobacterium carotovorum subsp. atrosepticum is also thought to be exported by T3SS, E. billingiae carries GSK525762 the srfABC gene cluster like the other three erwinias, but is lacking the instru mentation for a T3SS. The function Neuroblastoma of SrfC remains unclear, in consequence. Both pathogenic erwinias possess coding sequences for the SopA protein, which has been characterized as an effector like protein in Salmonella influencing the inflammatory response of mammalian hosts, This protein is translocated via the Salmonella T3SS on the SPI 1 into eukaryotic cells and seems to be necessary for full virulence, Since a similar T3SS has been identi fied in the pathogenic erwinias, one could assume that the SopA effector has a particular role in pathogenicity of those bacteria in plants.

It could influence proteins in the plant cell to alter defence response to bacterial GSK525762 invasion. Another putatively SPI 1 dependent system found in the four Erwinia species is composed of the small operon srfABC, which seems to be regulated by SPI 1 activation, Repression is accomplished by RcsB and PhoP, whose coding sequences could be identified in the erwin ias. For several effectors the SPI 1 related T3SS UNC2250 may has a special function, which is different to the hrp hrc T3SS but probably not essential for virulence because it is also present in the non pathogenic species E. tasmaniensis. This would be in accordance to rececently published results on SPI 1 mutants of E.

amylovora, The gene virK, which is secreted by the second Salmo nella T3SS found on the pathogenicity island GSK525762 2 and regulated by the phoPQ genes, is a pathogenicity fac tor of Salmonella sp, A coding sequence for VirK was identified in E. tasmaniensis and E. billingiae but not in the pathogenic erwinias. A possible reason could be the missing secretion system for this protein, which led to the loss of the gene in the process of specialization. The T3SS share a wide homology that could support secretion by the other systems found in the Erwinia species, A simple protein export machinery is built by the Type V secretion system, which is found in various bacte ria, The main domains, a leader sequence and an extracellular effector domain, and an outer membrane export channel, are sometimes encoded on one sequence and constitute one protein. Because of the self assembly and export they were termed autotransporters.

Another strategy, dubbed two partner secretion, is characterized by separate expression of leader effector protein and the leader channel protein. Most effector proteins are involved in adherence, invasion UNC2250 and degradation, The non pathogenic E. billingiae is the only species where we identified genes for corresponding autotrans porters, They show similarities to the AidA domain family, GSK525762 which is mainly present in enteropathogenic bacteria, and pertactin, an autotrans porter found in Bordetella sp, respectively. The primary role of the afore mentioned proteins is adherence to tar get structures. It may be possible that they substitute the function of missing fimbrial parts found in the other Erwinia species, a difference to strains Ep1 96 and Et1 99. An emerging class of secretion