View source for Avirulence Genes

Avirulence (Avr) genes  interact in a [[gene-for-gene interaction| gene-for-gene]] relation with [[Resistance genes |resistance genes]]. 
Viral Avr genes encode for coat proteins, replicase or movement proteins.
(Hammond-Kosack KE, Jones JD. PLANT DISEASE RESISTANCE GENES. Annu Rev Plant Physiol Plant Mol Biol. 1997 Jun;48:575-607 [http://www.ncbi.nlm.nih.gov/pubmed/15012275 PMID:15012275]).  

Recognized [[Effector |effectors]] are termed Avr proteins. (Jones JD, Dangl JL. The plant immune system. Nature. 2006 Nov 16;444(7117):323-9. [http://www.ncbi.nlm.nih.gov/pubmed/17108957 PMID: 17108957])


The term "avirulence genes" has been coined by H.H. Flor, as a result of the observation of the response of  [[Resistance genes| R-genes]] to direct o indirect products of pathogen genes, so named "avirulence genes".
Avr genes act in a dominant fashion and the response of the host occurs through the interaction with [[Resistance genes| R-genes]]. Avr genes can codify for a ligand recognised by a plant cell receptor which, in turn, can induce the defense response.
 [[File:Avr genes.jpg|thumb|800px|Interactions between pathogen Avr proteins and plant R proteins.]]
In this model, virulence is recessive and might arise from a loss of function mutation in the Avr gene or from a gain of function mutation in plant genome.
Most plant genomes contain different [[Resistance genes |resistance genes]], which confer them resistance to the attack of variable pathogens. The evolution of [[Resistance genes |R-genes]] is presmuably due to plant genome rearrangements.
(Richter TE, Ronald PC. The evolution of disease resistance genes.Plant Mol Biol. 2000 Jan;42(1):195-204. [http://www.ncbi.nlm.nih.gov/pubmed?term=PMID%3A%2010688137 PMID: 10688137]).


Since the discovery of Avr genes, molecular genetics reseaches have provided data about Avr genes that promote virulence in specific hosts not expressing the correspondeing [[Resistance genes| R-gene]]  (Figure, a).
Evolutionary developments can lead to the production of a resistance protein that recognizes directly or indirectly the Avr gene product and promotes a defense response (Figure, b and c).
(McDowell JM, Woffenden BJ.Plant disease resistance genes: recent insights and potential applications.Trends Biotechnol. 2003 Apr;21(4):178-83. [http://www.ncbi.nlm.nih.gov/pubmed?term=12679066 PMID:12679066]).

[[Category:Biology]]