Analysis of type III secretion system gene regulation of Dickeya dadantii 3937.

摘要

The soft rot pathogen Dickeya dadantii 3937 can attack a wide range of plant species. The type III secretion system (T3SS) and the pectinolytic enzymes secreted by the bacterium are required for full virulence. A Cya fusion protein was used to demonstrate that DspE, a putative T3SS effector, was delivered out of the bacterial cell through the T3SS. A global two-component signal transduction system, GacS/GacA, was shown to be involved in T3SS regulation by enhancing rsmB RNA production, which positively regulated HrpL (an alternative sigma factor responsible for T3SS gene expression downstream of T3S regulon) production. GacS/GacA also regulated pectinolytic enzyme production, suggesting that the expression of T3SS and pectinolytic enzymes were correlated. Using a green fluorescent protein (GFP) as a reporter, the expression pattern of pelD (encoding a major pectin-degrading enzyme) and dspE in host plants was investigated. DspE was highly expressed at an early stage after inoculation into host plants compared to PelD, while at a later stage of infection, PelD expression dominated DspE. Finally, HrpL was found to down-regulate pelD expression, suggesting a coregulation of T3SS and pectin catabolic pathways for the benefit of bacterial pathogenecity.;The expression of T3SS of plant bacterial pathogen is highly regulated. Although the plant apoplast environment, low pH, low temperature, and absence of complex nitrogen sources in media have been associated with the induction of T3SS genes of phytobacteria, no specific inducer has yet been identified. Here, two novel plant phenolic compounds, o-coumaric acid (OCA) and t-cinnamic acid (TCA), were identified to induce T3SS genes, while another plant phenolic compound, p-coumaric acid (PCA), was found to repress the expression of T3SS genes. The induction of T3SS expression by OCA and TCA may be partially due to the post-transcriptional regulation of the Gac-Rsm regulatory pathway. PCA repressed the expression of T3SS regulatory genes through the HrpX/Y two component system, a core regulator of the T3SS, rather than through the global regulator GacS/A.