Reactive Oxygen, NDR1 and NPR1 in Arabidopsis Disease Resistance Signaling

Chu Zhang and Allan D. Shapiro
The University of Delaware
Department of Plant and Soil Sciences
Newark, DE 19716
zhangchu@udel.edu
(302) 831-0854

 Mutants in the NDR1 gene are compromised in resistance to multiple
strains of Pseudomonas syringae and Peronospora  parasitica. ndr1
mutants are also affected in specific processes correlated with disease
resistance in a pathogen strain-specific manner. Previous work has
suggested that NDR1   acts downstream of the oxidative burst and upstream
of induced salicylic acid (SA) biosynthesis.  This model would predict
that levels of reactive oxygen production seen early in the response to
avirulent pathogen should not be affected by the ndr1 mutation. A burst
of hydrogen peroxide production was seen between 2 and 5 hours
post-inoculation with P. syringae pv. tomato DC3000 carrying avrB or
avrRpt2.  No significant differences were noted between ndr1-1 and the
Columbia parental. We have made an ndr1-1/npr1-2 double mutant.  The npr1
mutation was not found to have any affects on the hypersensitive response
(HR) either in the single or the double mutant.  As such we conclude that
the signaling pathway downstream of npr1 and any feedback affected by the
npr1 mutation do not contribute to the HR.  Analysis of PR-1, PR-2 and
PR-5 induction in single and double mutants in response to both virulent
and avirulent P. syringae  showed that cell death and SA make independent
contribution to PR gene induction.