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Published online: 29 August 2007 | doi:10.1038/nchina.2007.175

Plant pathogens: Two loops, one defence

Wei Zeng

Introduction

© (2007) Nature

P. syringae is a pathogen that can infect a large range of plants. It attacks tomato plants by injecting effector proteins, known as AvrPto, into plant cells. Tomato plants that have evolved with certain resistance proteins can fight off these effector proteins by triggering cell death, and thereby limiting pathogen growth. Scientists used to think that AvrPto triggers this immune system response by increasing Pto activity, the protein kinase of these resistance proteins. Jijie Chai at the National Institute of Biological Sciences in Beijing and co-workers¹ have now shown that AvrPto actually inhibits Pto kinase activity.

The researchers first determined the crystal structure of the AvrPto–Pto complex, which comprises two loops, one on top of the other that AvrPto binds to (pictured). The interface of the first loop is mainly hydrophobic whereas the interface of the second loop has both hydrogen bonds and a hydrophobic interaction. An active conformation of the second loop is needed for AvrPto to form stable bonds with Pto.

The researchers next showed that AvrPto–Pto binding inhibits Pto activity by interacting with Pto's two structural loops. However, the inhibition is not the signal to activate resistance proteins. The researchers think that the two loops of Pto lock the resistance proteins into an inactive mode. The AvrPto–Pto binding leads to conformational changes in Pto, which unlock and activate the proteins.

The authors of this work are from:
National Institute of Biological Sciences, Beijing, China; Institute of Biophysics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China; Cornell High-Energy Synchrotron Source, Cornell University, Ithaca, New York, USA; Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, China.

Reference

1. Xing, W. et al. The structural basis for activation of plant immunity by bacterial effector protein AvrPto. Nature doi: 10.1038/nature06109 (2007).  | Article |