Fungal avirulence genes: structure and possible functions

Area of Science:

• Plant pathology
• Molecular genetics
• Fungal genetics

Background:

• Avirulence (Avr) genes in fungi dictate host specificity in gene-for-gene plant-pathogen interactions.
• These genes prevent disease on plants with corresponding resistance (R) genes, triggering plant defense responses.
• Avr gene products, or elicitors, interact with plant receptors, often leading to a hypersensitive response.

Purpose of the Study:

• To review the cloning and molecular analysis of fungal Avr genes.
• To discuss the known and potential functions of Avr gene products.
• To explore the application of Avr and R genes in engineering plant resistance.

Main Methods:

• Avr genes have been isolated using techniques such as reverse genetics and positional cloning.
• Molecular analyses of nonfunctional Avr alleles reveal mutations or deletions in coding or promoter regions.
• Bioinformatic predictions and experimental studies characterize Avr gene products, often as extracellular proteins.

Main Results:

• Several cultivar-specific (e.g., Avr4, Avr9, Ecp2, nip1, Avr2-YAMO) and species-specific (e.g., PWL1, PWL2, inf1) fungal Avr genes have been successfully cloned.
• Ongoing efforts aim to isolate additional Avr genes from various fungal species.
• Some Avr gene products, like those from nip1 and Ecp2, function as essential pathogenicity factors.

Conclusions:

• Fungal Avr genes are crucial for understanding plant disease resistance.
• Elucidating Avr gene mechanisms and their interaction with R genes is key for developing durable crop protection.
• Exploiting Avr-R gene systems offers promising avenues for engineered resistance against fungal pathogens.