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Microbial avirulence determinants: guided missiles or antigenic flak?

Paraskevi Skamnioti¹, Christopher J Ridout

¹Department of Disease and Stress Biology, John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK.

Molecular Plant Pathology

|June 23, 2010

Summary

Avirulence (avr) determinants are microbial molecules that trigger plant defenses. While some aid pathogen virulence, many don't, raising questions about their essential function and evolutionary persistence.

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Area of Science:

Plant pathology
Microbial genetics
Evolutionary biology

Background:

Avirulence (avr) determinants are microbial factors eliciting plant defense responses via gene-for-gene interactions.
Recognition of avr determinants by plant resistance genes is well-studied, but their evolutionary purpose remains debated.
Many bacterial avr determinants function as effectors contributing to virulence, but this is not universally observed.

Purpose of the Study:

To review the literature on avirulence determinants and investigate their potential functions.
To address the paradox of why microbes retain genes that signal their presence to hosts.
To explore explanations for the observed lack of virulence defects in many avr gene mutants.

Main Methods:

Literature review of accumulating research on avirulence determinants.
Analysis of existing data on the functional roles of avr genes in various pathogens.
Synthesis of arguments regarding the evolutionary maintenance of avr genes.

Main Results:

While some avr determinants are effectors essential for virulence, many are not.
Functional redundancy is proposed to explain the lack of virulence defects in avr mutants.
The persistence of non-essential avr genes presents an evolutionary paradox.

Conclusions:

The precise function of many avr determinants remains elusive.
The evolutionary advantage or necessity for retaining avr genes requires further investigation.
Understanding avr determinant function is crucial given the increasing identification of these genes.