Characterization of the Fenthion response in tomato and the identification of genes that encode Fen-interacting proteins
Abstract
The Fen gene encodes a serine-threonine kinase and confers sensitivity of tomato to the fenthion family of organophosphorous insecticides. Fen belongs to a gene family that includes Pto, a gene encoding another serine-threonine kinase. Tomatoes expressing the Pto gene are resistant to Pseudomonas syringae pv. tomato strains expressing the avirulence gene avrPto. Pto plays a part in recognition of AvrPto and is likely responsible for the activation of downstream signal transduction pathway components. Another tomato gene, Prf, is required for fenthion sensitivity and Pto-mediated resistance. Sequence similarity between Fen and Pto and their dependence on Prf, led to the hypothesis that they activate similar responses. I have shown that several aspects of fenthion sensitivity are similar to the resistance response mediated by Pto. Sensitivity results in macroscopic cell death similar in timing and appearance to the hypersensitive cell death observed during incompatible pathogen interactions. Fenthion sensitivity also results in the induction of defense gene expression, and the elicitation of systemic acquired resistance. This indicates that the Fen- and Pto-mediated signal transduction pathways share components of a common signal transduction pathway and have independent components that work in parallel to activate the same defense responses. To characterize the Fen-mediated signal transduction pathway further I have used the yeast two-hybrid system to search for proteins that interact directly with Fen. Using this system, I have isolated five classes of genes that encode Fen-interacting (Fni) proteins. Members of these classes do not interact with Pto or any other known Pto-pathway components in the two-hybrid system but sequence analysis suggests they might have a role in signal transduction or defense responses. One of the genes isolated, Fni2, encodes a protein that is phosphorylated by both Fen and Pto. Fni2 also shows an interaction with both Fen and Pto using an in vitro binding assay. Transient co-expression of an antisense construct of Fni2 with avrPto in tobacco expressing Pto resulted in a delay and weakening of the hypersensitive response. Although the deduced amino acid sequence of Fni2 revealed no insights into its function, the striking conservation of the protein among eukaryotes suggests a conserved function.
Degree
Ph.D.
Advisors
Martin, Purdue University.
Subject Area
Plant pathology|Genetics|Botany
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