Honour McCann

From

Honour McCann

Supervisor: David Guttman, Department of Ecology and Evolutionary Biology and Department of Cell and Systems Biology

WiP Seminar, 20 January 2009

Identification of novel innate immunity elicitors using molecular signatures of natural selection

The innate immune system protects eukaryotes against invading microbes upon perception of microbial motifs called pathogen-associated molecular patterns (PAMPs). Despite their central role in innate immunity, and their potential as antimicrobial agents, few PAMPs have been identified, and no systematic method has been developed for their discovery.

We show that competing signatures of negative selection to preserve core functions, and positive selection to avoid host recognition can be used to identify novel PAMPs. A selection analysis confirmed that all 1322 core genes identified from six phytopathogenic bacteria exhibited strong negative selection at the whole-gene level, while 56 genes also showed localized regions of positive selection. We show that these candidate PAMPs differ from the core genome with respect to the number and clustering of positively-selected sites. Finally, we functionally confirmed the candidates' ability to induce innate immunity in Arabidopsis thaliana via callose deposition and virulence suppression assays.

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