Constitutive salicylic acid‐dependent signaling in cpr1 and cpr6 mutants requires PAD4

Abstract

SummarySalicylic acid (SA)-dependent signaling controls activation of a set of plant defense mechanisms that are important for resistance to a variety of microbial pathogens. Many Arabidopsis mutants that display altered SA-dependent signaling have been isolated. We used double mutant analysis to determine the relative positions of the pad4, cpr1, cpr5, cpr6, dnd1 and dnd2 mutations in the signal transduction network leading to SA-dependent activation of defense gene expression and disease resistance. The pad4 mutation causes failure of SA accumulation in response to infection by certain pathogens, while the other mutations cause constitutively high levels of SA, defense gene expression and resistance. The cpr1 pad4, cpr5 pad4, cpr6 pad4, dnd1 pad4 and dnd2 pad4 double mutants were constructed and assayed for stature, presence of spontaneous lesions, resistance to Pseudomonas syringae and Peronospora parasitica, SA levels, expression of PAD4, PR-1 and PDF1.2, and accumulation of camalexin. We found that the effects of the cpr1 and cpr6 mutations on SA-dependent gene expression are completely dependent on PAD4 function. In contrast, SA accumulation in the lesion-mimic mutant cpr5 is partially PAD4-independent, while in dnd1 and dnd2 mutants it is completely PAD4-independent. A model describing a possible arrangement of activities in the signal transduction network is presented.

Leaf Senescence Signaling: The Ca2+-Conducting Arabidopsis Cyclic Nucleotide Gated Channel2 Acts through Nitric Oxide to Repress Senescence Programming

“…Previous studies have reported that spontaneous necrotic lesions can appear in dnd1 leaves (Clough et al, 2000;Jirage et al, 2001). Here, our observation further expands our understanding of the dnd1 mutant phenotype.…”

“…In addition to involvement in pathogenmediated Ca 2+ signaling, CNGC2 has been suggested to participate in the process of leaf development/ senescence (Kö hler et al, 2001). dnd1 mutant plants have high levels of SA and expression of PR1 (Yu et al, 1998), and spontaneous necrotic lesions appear conditionally in dnd1 leaves (Clough et al, 2000;Jirage et al, 2001). Endogenous H 2 O 2 levels in dnd1 mutants are increased from wild-type levels (Mateo et al, 2006).…”

Constitutive disease resistance requires EDS1 in the Arabidopsis mutants cpr1 and cpr6 and is partially EDS1‐dependent in cpr5

“…Signi®cantly, pad4 suppressed cpr1-and cpr6-induced resistance to P.s. maculicola ES4326 and P. parasitica Noco2, and SAdependent PR gene expression (Jirage et al, 2001). Also, pad4 partially suppressed cpr5-induced pathogen resistance, but had no signi®cant effect on SA accumulation or PR gene induction.…”

“…In contrast, eds1 only partially suppresses resistance in cpr5, leading us to conclude that cpr5 expresses both EDS1-dependent and EDS1-independent components of plant resistance. Jirage et al (2001) show in an accompanying paper that the cpr1-, cpr5-and cpr6-conditioned phenotypes have similar requirements for the SA regulatory gene PAD4 as for EDS1. We conclude that EDS1 and PAD4 have similar positions in the cpr-induced signaling cascades.…”

“…In a parallel study, Jirage et al (2001) performed genetic epistasis analysis between the SA regulatory mutant pad4 and cpr1, cpr5 and cpr6. PAD4 was found to be required for the same cpr-induced resistance phenotypes as eds1, suggesting that EDS1 and PAD4 function at a similar position in the cpr-driven signaling network.…”