In collaboration with Agilent Technologies and the University of Geneva, we have designed custom microarrays that can take 'genetic snapshots' of Pectobacterium atrosepticum (Pba), Dickeya dadantii (Dda), and potato (Ravirala et al., 2007), at precise moments in the disease process. We also have access to Affymetrix microarrays for Phytophthora infestans. These arrays allow us to monitor the gene expression levels in the organisms that cause plant disease, and the responses made by the host plant.

Microarrays measure the levels of expression of individual genes in each organism. By studying the ways in which these change over time, we can construct a picture of how the genetic circuits of the pathogen and plant respond to each other during the disease process.

For the direct, high-throughput investigation of bacterial and oomycete genomes we have developed a transposon mutation grid approach. The mutation grid technology developed at SCRI gives us the ability to measure the effects on disease of removing one gene at a time from the invading pathogen. Careful analysis of these 'knockouts' using microarray and other technologies allows us to piece together the pathogenic mechanisms of pathogens, and discover the important genetic components that lead to disease on the host plant.

References

• Ravirala, R.S., Barabote, R.D., Wheeler, C.M., Reverchon, S., Tatum, O., Malouf, C., Toth, I.K., Lui, H. and Michael, J.D. San Francisco. 2006. Efflux pump gene expression in E. chrysanthemi is induced by exposure to phenolic acids. Molecular Plant-Microbe Interactions 20, 313-320.
• Venkatesh B., Babujee L., Liu H., Hedley P., Fujikawa T., Birch P., Toth I.K. and Tsuyumu S. 2006. Erwinia chrysanthemi 3937 PhoQ sensor kinase regulates several virulence determinants. The Journal of Bacteriology 188, 3088-3098.