Thursday, April 12, 2007

Great news in plant pathology!

This study shows for the first time that a resistance gene product from the plant (in this case the N gene from tobacco) and an elicitor from the plant pathogen (p50 from Tobacco Mosaic Virus [TMV]) physically interact during the plant defense response. This evidence has been illusive so far.

A Novel Role for the TIR Domain in Association with Pathogen-Derived Elicitors Burch-Smith TM, Schiff M, Caplan JL, Tsao J, Czymmek K, et al. PLoS Biology Vol. 5, No. 3, e68 doi:10.1371/journal.pbio.0050068

(Thanks to the Evilutionary Biologist whose link to PLoS I followed to discover this paper).

The N gene from tobacco and other related solanaceous plants confers resistance to the plant host against the plant pathogenic virus TMV (Tobacco Mosaic Virus). An elicitor is a protein that comes from the pathogen, and enters to host cell. Numerous papers have given indirect evidence of elicitors being recognized inside the host cell by plant proteins (often the actual resistance gene products), and setting off signal transduction cascades that result in a resistance response. In plants a resistance response is most often associated by rapid cell death of the host tissue in a localized (small) area. This is called the hypersensitive response, and the theory is that this cell death is a form of apoptosis (programmed cell death) to prevent to plant pathogen from spreading to surrounding tissues.

In many plant host-plant pathogen systems, interaction of a resistance gene product with an elicitor molecule could be shown in the lab (in vitro), but it was never shown in a life plant (in vivo) before. Until now.

One of the TMV elicitors is the p50 protein. The p50 proteins appears to interact physically with the protein encoded by the tobacco resistance gene N. They do so both in the cytoplasm and the nucleus of the host.

The N gene was always suspected of being involved in protein-protein interactions, because of the presence of the LRR domain. The LRR (Leucine Rich Repeat) domain, is found in a many proteins, in many different organisms, and is usually responsible for interacting with other proteins. This paper however, shows that the TIR (Toll-interleukin 1 receptor homology domain ; another part of the N protein) is crucial for the interaction with p50. This domain is named after a receptor molecule found in animals that is involved in innate immunity, a rapid response against pathogen invasion.

In future posts I will explain the background of the research and the basics of plant pathology some more.

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