Poster: Plant Pathogen/Symbiont Interactions

Abs # 741: Knockout of the Arabidopsis NPR1-related gene, NPR4, compromises defense responses

Presenter:	Liu, Guosheng , guosheng.liu@nrc-cnrc.gc.ca
Authors	Liu, Guosheng  (A)   Alonso, Jose M. (B) (C)  Ecker, Joseph R. (C)   Fobert, Pierre  (A)
Affiliations:	(A): National Research Council of Canada / Plant Biotechnology Institute (B): Department of Genetics, North Carolina State University (C): The Salk Institute

Sequencing of the Arabidopsis genome revealed that there are six members to the NPR1/NIM1 gene family. Given the pivotal role played by NPR1/NIM1 in controlling systemic acquired disease resistance, functional characterization of each member of this family appeared to be justified. In this study, reverse genetics were utilized to analyze the role of one NPR1/NIM1-like gene, which we called NPR4, that encodes a protein with 36% identity to NPR1. T-DNA knockout of NPR4 has no obvious developmental phenotypes, but plants are more susceptible to both virulent and avirulent strains of the bacterial pathogen Pseudomonas syringe pv tomato DC3000 (Pst) as well as to the fungal pathogen Erysiphe cichoracearum. The enhanced disease susceptibility phenotype of the npr4 mutant could be complemented by expression of a wild-type NPR4 transgene, and was consistently observed to be milder than that of the npr1-3 mutant. Whereas npr1 mutants fail to accumulate transcripts of pathogenesis-related genes such as PR1, PR2, and PR5 following treatment with salicylic acid (SA), expression of these genes is only marginally reduced in the npr4 mutant. In wild-type plants, NPR4 is expressed predominantly in young leaves. It is rapidly induced by pathogen challenge and SA treatment, and is repressed by the jasmonic acid (JA) signaling pathway, suggesting that NPR4 could be implicated in the cross-talk between the SA and JA pathways.