| Pectobacterium species are enterobacterial plant pathogens that cause soft rot disease in diverse plant species. The type III secretion system (T3SS) of Pectobacterium carotovorum subsp. carotovorum (P. carotovorum) appears to secrete only one effector protein, DspE. HrpL, the alternative sigma factor responsible for regulating the T3SS operon, and DspE are required for P. carotovorum pathogenesis on host leaf tissue. In this work, we present data that support the hypothesis that the role of DspE is to initiate pathogenesis by causing host cell death via autophagy. To initiate autophagy, DspE requires its full length and WxxxE-like motifs, which are important for effector proteins in diverse bacterial pathogens of plants and animals. Further, analysis of P. carotovorum gene expression in planta indicated that HrpL and DspE expression activates expression of a large number of genes outside of the T3SS operon, suggesting that host cell death caused by DspE subsequently activates expression of a large number of genes involved in soft-rot pathogenesis. Deletion of dspE eliminates the ability P. carotovorum to cause symptoms on leaves, however, when leaf tissue was constantly misted with water after inoculation, the dspE mutant strain was able to initiate disease, suggesting that acquisition of dspE and the T3SS enables P. carotovorum to initiate disease at lower ambient humidity. |
