Molecular dialog between two ingenious opponents-plants and pathogenic bacteria
published: Feb. 24, 2014, recorded: February 2014, views: 2307
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Pseudomonas syringae pv. phaseolicola is the causative agent of halo blight in Phaseolus vulgaris L., the common bean. Similar to other pathogenic Gram-negative bacteria, P. syringae delivers type III virulence factors into host cells. These factors are subject to the competing forces of improved pathogenesis and avoidance of recognition by the host. This concept is particularly well illustrated by HopQ1 (for Hrp outer protein Q), which functions to promote disease development in the bean and tomato. However, HopQ1 is sensed by Nicotiana spp., which has evolved systems to respond to its presence. The mechanistic explanation for this phenomenon has not yet been provided. We found that HopQ1, after specific phosphorylation, associates with host 14-3-3 proteins, a highly-conserved family of proteins that function as regulators of their partner proteins. We confirmed the physical interaction between HopQ1 and 14‐3‐3a using FRET‐FLIM techniques. A mutation that prevented binding between 14-3-3 and HopQ1 proteins affected the cellular distribution and stability of the effector and slightly compromised bacterial growth in the bean. Interestingly, tobacco plant recognition of HopQ1 was not altered by that mutation, which suggests the presence of separate virulence and avirulence determinants. We are currently analyzing structures of monomeric and oligomeric forms of HopQ1 and the complex of HopQ1 with 14-3-3a, using MALS (multiangle light scattering analysis) combined with size exclusion chromatography and SAXS (small angle X-ray scattering) techniques supported by molecular modeling. Results so far will be presented.
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