Plant resistance genes: their structure, function and evolution

Plants have developed efficient mechanisms to avoid infection or to mount r esponses that render them resistant upon attack by a pathogen. One of the b est-studied defence mechanisms is based on gene-for-gene resistance through which plants, harbouring specific resistance (R) genes, specifically recog nise pathogens carrying matching avirulence (Avr) genes. Here a review of t he R genes that have been cloned is given. Although in most cases it is not clear how R gene encoded proteins initiate pathways leading to disease res istance, we will show that there are clear parallels with disease preventio n in animal systems. Furthermore, some evolutionary mechanisms acting on R genes to create novel recognitional specificities will be discussed.