| In order to survive in an ever changing and constantly challenging environment, plants must be able to tightly control gene expression. Strict regulation is essential for plant fitness because stress responses take energy and resources away from growth and development. Pathogen attack is one challenge in which plants initiate massive gene expression changes. Using genomic and genetic methods, I found novel transcriptional regulators that play important roles in the interaction between the bacterial pathogen Pseudomonas syringae and the model plant Arabidopsis thaliana.;The development of microarray technology has made it possible to look at transcript levels on a genome-wide scale. Using this tool, I analyzed the expression profile of nearly all Arabidopsis genes at several time points following infection with P. syringae. Interestingly, a set of genes that are involved in the production of the defense signaling molecule salicylic acid showed a similar expression pattern. I found a novel cis-regulatory element that is enriched among the promoters of this set of genes. By creating a series of transgenic promoter::GUS plants to monitor expression levels, I showed that this cis-element plays a role in controlling gene expression during disease resistance.;I also discovered three transcription factors that control the expression of a subset of genes following infection with P. syringae. These highly similar members of the NAC transcription factor family, ANAC019, ANAC055, and ANAC072, are induced by infection with P. syringae. This induced expression is dependent on the plant hormone abscisic acid and the bacterial-produced toxin coronatine, both of which have been shown to promote susceptibility to infection. I created an anac019 anac055 anac072 triple mutant and found that it was more resistant to infection with P. syringae. Using this triple mutant, I showed that the induction of several downstream targets of coronatine is dependent on these transcription factors.;In summary, I found a novel cis-regulatory element and three transcription factors that play important roles in the transcriptional regulation of plant disease resistance. |
