Article Figures & Data
Figures
- Figure 1.
Camalexin Levels in Wild-Type and pad4 Plants after Various Treatments.
Each data point represents the mean and standard deviation of six replicate samples.
(A) Infection with P. s. maculicola ES4326 or P. s. maculicola ES4326 carrying avrRpt2. wt-Psm, wild-type plants infected with P. s. maculicola ES4326; pad4-Psm, pad4 plants infected with P. s. maculicola ES4326; wt-avr, wild-type plants infected with P. s. maculicola ES4326 carrying avrRpt2; pad4-avr, pad4 plants infected with P. s. maculicola ES4326 carrying avrRpt2.
(B) Infection with X. c. campestris (Xcc) BP109.
(C) Spraying with 5 mM silver nitrate.
- Figure 2.
Defense Gene Expression in Leaves Infected with P. s. maculicola ES4326 or P. s. maculicola ES4326 Carrying avrRpt2.
Leaves were excised at 0, 12, 24, 36, or 48 hr after infection. Mg indicates leaves mock inoculated with 10 mM MgSO4 sampled at 36 hr. rRNA indicates hybridization with an 18S rRNA probe used to evaluate equal loading.
(A) Infection with P. s. maculicola ES4326.
(B) Infection with P. s. maculicola ES4326 carrying avrRpt2.
- Figure 3.
Exogenous SA Induces PR-1 Expression and Enhanced Resistance to P. s. maculicola ES4326 in Wild-Type and pad4 Plants.
Plants were sprayed with 5 mM SA in 0.02% [v/v] Silwet L-77 or with 0.02% Silwet alone until uniformly wet.
(A) PR-1 expression in response to SA. Samples were taken daily after spraying. The c indicates control; plants were sprayed with 0.02% Silwet alone and sampled at 3 days after spraying.
(B) Effect of spraying plants with SA on P. s. maculicola ES4326 growth. One day after treatment, plants were infected with P. s. maculicola ES4326 at a dose of 103 cfu/cm2. Bacterial titer was determined 3 days after infection. Each bar represents the mean and standard deviation of eight replicates. Similar results were obtained in three other independent experiments. −SA, plants not treated with SA before infection; +SA, plants treated with SA before infection; wt, wild type.
- Figure 4.
Camalexin Accumulation in Wild-Type and nahG Plants Infected with Pathogens.
Wild-type (wt) Ler and Ler nahG transgenic plants were infected with either P. s. maculicola (Psm) ES4326 or P. s. maculicola ES4326 carrying avrRpt2 at a dose of 105 cfu/cm2. Camalexin in the infected leaves was determined at the times that camalexin levels are high in wild-type plants: 24 hr after infection for P. s. maculicola ES4326 carrying avrRpt2 and 32 hr after infection for P. s. maculicola ES4326. Each bar represents the mean and standard deviation of eight replicate samples.
- Figure 5.
SA and SAG Levels in Infected Wild-Type and pad4 Plants.
Wild-type (wt) and pad4 plants were infected with P. s. maculicola ES4326 (Psm), P. s. maculicola ES4326 carrying avrRpt2 (Psm avr), or mock infected with 10 mM MgSO4 (mock). Each column represents the mean of three replicate samples. Error bars representing the standard deviation are shown where they are large enough to be visible. SA and SAG were assayed on the same samples. The experiments with P. s. maculicola ES4326 and with P. s. maculicola ES4326 carrying avrRpt2 were conducted at different times; therefore, results should not be compared directly.
(A) SA levels in plants infected with P. s. maculicola ES4326.
(B) SA levels in plants infected with P. s. maculicola ES4326 carrying avrRpt2.
(C) SAG levels in plants infected with P. s. maculicola ES4326.
(D) SAG levels in plants infected with P. s. maculicola ES4326 carrying avrRpt2.
- Figure 6.
SA Application before P. s. maculicola ES4326 Infection Restores Camalexin Accumulation and PR-1 Expression in pad4 Plants.
Wild-type (wt) and pad4 plants were treated either with 5 mM SA in 0.02% [v/v] Silwet L-77 or with 0.02% Silwet alone 1 day before infection with P. s. maculicola ES4326.
(A) Effect of exogenous SA on camalexin levels in P. s. maculicola ES4326–infected plants. Infected leaves were sampled 2 days after infection. Each data point represents the mean and standard deviation of six replicates.
(B) Effect of exogenous SA on PR-1 expression in P. s. maculicola ES4326–infected plants. Leaves infected with P. s. maculicola ES4326 were sampled from mock-treated wild-type and pad4 plants (lanes 3 and 7) and SA-treated plants (lanes 4 and 8) 2 days after infection. For comparison, mock-treated plants were sampled 1 and 2 days after treatment (lanes 1 and 9, respectively, for the wild type; lanes 5 and 11, respectively, for pad4), as were SA-treated plants (lanes 2 and 10, respectively, for the wild type; lanes 6 and 12, respectively, for pad4). Similar results were obtained in another independent experiment. (+) and (−) in the row labeled SA indicate the presence or absence of SA treatment, repectively. (+) and (−) in the row labeled Psm indicate the presence or absence of P. s. maculicola ES4326 infection, respectively. Because of the strong PR-1 signal in leaves infected with P. s. maculicola ES4326, the exposure for this blot was shorter than was the exposure for the blot shown in Figure 3A; consequently, the expression of PR-1 48 hr after SA treatment appears lower than it does in Figure 3A.
- Figure 7.
Model for the Role of PAD4 in Signal Transduction.
When plants are infected with P. s. maculicola (Psm) ES4326, PAD4 function is needed for SA accumulation and activation of defense responses that require SA, such as camalexin synthesis and PR-1 expression. When plants are infected with P. s. maculicola ES4326 carrying avrRpt2, SA accumulation occurs by a PAD4-independent mechanism.
