What recognizes what in plant disease resistance?

In a new study published online this week in the open-access journal PLoS Biology, Tessa Burch-Smith, Savithramma Dinesh-Kumar, and colleagues show how one aspect of the plant immune system is defined by the gene-for-gene hypothesis: a plant Resistance (R) gene encodes a protein that specifically recognizes and protects against one pathogen or strain of a pathogen carrying a corresponding Avirulence (Avr) gene.

In tobacco and its relatives, the N resistance protein confers resistance to infection by the Tobacco mosaic virus (TMV). The authors used N, and the TMV Avirulence gene, p50, to investigate the mechanism of gene-for-gene resistance. Contrary to current models, which propose that recognition of resistance genes occurs solely through their leucine-rich repeat domain, the authors show that association is mediated by a completely different region on N's Toll-interleukin-1 receptor homology domain, which is structurally similar to animal innate immunity molecules. These findings provide novel insights into how R proteins recognize pathogen Avr proteins and should help in long-term efforts to enhance crop yield.