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Salicylic Acid and NIM1/NPR1-Independent Gene Induction by Incompatible Peronospora parasitica in Arabidopsis

October 2001 , Volume 14 , Number  10
Pages  1,235 - 1,246

Gregory J. Rairdan , Nicole M. Donofrio , and Terrence P. Delaney

Cornell University, Department of Plant Pathology, 360 Plant Science Building, Ithaca, NY 14853, U.S.A.

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Accepted 27 June 2001.

To identify pathogen-induced genes distinct from those involved in systemic acquired resistance, we used cDNA-amplified fragment length polymorphism to examine RNA levels in Arabidopsis thaliana wild type, nim1-1, and salicylate hydroxylase-expressing plants after inoculation with an incompatible isolate of the downy mildew pathogen Peronospora parasitica. Fifteen genes are described, which define three response profiles on the basis of whether their induction requires salicylic acid (SA) accumulation and NIM1/NPR1 activity, SA alone, or neither. Sequence analysis shows that the genes include a calcium binding protein related to TCH3, a protein containing ankyrin repeats and potential transmembrane domains, three glutathione S-transferase gene family members, and a number of small, putatively secreted proteins. We further characterized this set of genes by assessing their expression patterns in each of the three plant lines after inoculation with a compatible P. parasitica isolate and after treatment with the SA analog 2,6-dichloroisonicotinic acid. Some of the genes within subclasses showed different requirements for SA accumulation and NIM1/NPR1 activity, depending upon which elicitor was used, indicating that those genes were not coordinately regulated and that the regulatory pathways are more complex than simple linear models would indicate.

Additional keywords: calmodulin, CXc750, ECS1, gene expression profiling, NahG plants, ORFX.

© 2001 The American Phytopathological Society