Disease resistance to fungal diseases

Background on Resistance (R) genes and avirulence (Avr) genes ([http://www.annualreviews.org/doi/full/10.1146/annurev.arplant.48.1.575 Hammond-Kosack & Jones 1997)

-R genes are found in the plant, while corresponding Avr gene is in the pathogen -presumed roles of R genes:

1. help plants detect pathogenic Avr gene products
2. initiate signal transduction pathways that will help defend against the pathogen
3. "have the capacity to evolve new R gene specificities rapidly"

-if the R gene or corresponding pathogenic Avr gene are not present or altered, then plant is infected with the disease

The R protein recognizes the Avr gene product (ligand), activating a signal transduction cascade that initiates the defense against the pathogen. Thus, the R gene is turned on in healthy plants. R proteins must be able to evolve quickly in order to target new pathogens specifically. The evolution of the Avr genes directly impacts the evolution of the related R gene (coevolution).