Pathogens Double Down

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Science  24 Aug 2012:
Vol. 337, Issue 6097, pp. 891
DOI: 10.1126/science.337.6097.891-a

Bacterial spot that affects tomato and pepper plants is caused by Xanthomonas campestris. X. campestris delivers a protein effector called XopN into plant cells that binds to other proteins, including the 14-3-3 protein in tomatoes, TFT1. 14-3-3 proteins serve variously as clamps, masks, and scaffolds to regulate and organize the functions of a wide variety of target proteins. Taylor et al. studied how the interaction of XopN with TFT1 modulated the plant's pathogen defense response. Silencing of the gene that encodes TFT1 demonstrated that it plays a protective role against bacterial infection and regulates four other pathogentriggered plant genes. TFT1 was able to keep the growth of XopN-deficient bacteria in check, but this effect was abrogated in the absence of TFT1.

XopN binds to TFT1 through its C-terminal domain. XopN also binds to TARK1, a tomato atypical receptor kinase that plays a role in plant defense, through its N-terminal domain, and this binding interaction seems to help the XopN C-terminal domain hold on to TFT1. Through its two-domain binding system, the bacterial XopN effector sequesters the two plant-defense proteins. It is not clear yet just how TFT1 and TARK1 defend the plant normally, but what is clear is that when XopN grabs both of them together, the plant's defense collapses.

PLoS Pathog. 8, e1002768 (2012).

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