Systemic Acquired Resistance

740

595

Induced resistance protects plants against a wide spectrum of diseases; however, it can also entail costs due to the allocation of resources or toxicity of defensive products. The cellular defense responses involved in induced resistance are either activated directly or primed for augmented expression upon pathogen attack. Priming for defense may combine the advantages of enhanced disease protection and low costs. In this study, we have compared the costs and benefits of priming to those of induced direct defense in Arabidopsis. In the absence of pathogen infection, chemical priming by low doses of ␤-aminobutyric acid caused minor reductions in relative growth rate and had no effect on seed production, whereas induction of direct defense by high doses of ␤-aminobutyric acid or benzothiadiazole strongly affected both fitness parameters. These costs were defense-related, because the salicylic acid-insensitive defense mutant npr1-1 remained unaffected by these treatments. Furthermore, the constitutive priming mutant edr1-1 displayed only slightly lower levels of fitness than wild-type plants and performed considerably better than the constitutively activated defense mutant cpr1-1. Hence, priming involves less fitness costs than induced direct defense. Upon infection by Pseudomonas syringae or Hyaloperonospora parasitica, priming conferred levels of disease protection that almost equaled the protection in benzothiadiazole-treated wild-type plants and cpr1 plants. Under these conditions, primed plants displayed significantly higher levels of fitness than noninduced plants and plants expressing chemically or cpr1-induced direct defense. Collectively, our results indicate that the benefits of priming-mediated resistance outweigh the costs in environments in which disease occurs.induced resistance ͉ innate immunity ͉ plant defense

mentioning

confidence: 99%

Costs and benefits of priming for defense in Arabidopsis

Hulten

Pelser

Loon

et al. 2006

740

595

“…A classic example is systemic acquired resistance (SAR) that is activated after infection by a necrotizing pathogen. SAR has been demonstrated in many plant species and confers resistance against a broad spectrum of plant pathogens in distant, uninfected plant parts (25). Selected nonpathogenic, rhizosphere-colonizing Pseudomonas bacteria trigger a phenotypically similar form of resistance, called rhizobacteria-mediated induced systemic resistance (ISR) (26).…”

mentioning

confidence: 99%

Enhancement of induced disease resistance by simultaneous activation of salicylate- and jasmonate-dependent defense pathways in Arabidopsis thaliana

Wees

Swart²,

Pelt³

et al. 2000

529

296

The plant-signaling molecules salicylic acid (SA) and jasmonic acid (JA) play an important role in induced disease resistance pathways. Cross-talk between SA-and JA-dependent pathways can result in inhibition of JA-mediated defense responses. We investigated possible antagonistic interactions between the SA-dependent systemic acquired resistance (SAR) pathway, which is induced upon pathogen infection, and the JA-dependent induced systemic resistance (ISR) pathway, which is triggered by nonpathogenic Pseudomonas rhizobacteria. In Arabidopsis thaliana, SAR and ISR are effective against a broad spectrum of pathogens, including the foliar pathogen Pseudomonas syringae pv. tomato (Pst). Simultaneous activation of SAR and ISR resulted in an additive effect on the level of induced protection against Pst. In Arabidopsis genotypes that are blocked in either SAR or ISR, this additive effect was not evident. Moreover, induction of ISR did not affect the expression of the SAR marker gene PR-1 in plants expressing SAR.Together, these observations demonstrate that the SAR and the ISR pathway are compatible and that there is no significant cross-talk between these pathways. SAR and ISR both require the key regulatory protein NPR1. Plants expressing both types of induced resistance did not show elevated Npr1 transcript levels, indicating that the constitutive level of NPR1 is sufficient to facilitate simultaneous expression of SAR and ISR. These results suggest that the enhanced level of protection is established through parallel activation of complementary, NPR1-dependent defense responses that are both active against Pst. Therefore, combining SAR and ISR provides an attractive tool for the improvement of disease control.

“…The most ubiquitous plant defense response includes a hypersensitive response (HR) or localized cell death at the site of pathogen ingress. The local HR often leads to a nonspecific general defense response throughout the plant called systemic acquired resistance (3).…”

mentioning

confidence: 99%

Alternatively spliced N resistance gene transcripts: Their possible role in tobacco mosaic virus resistance

Dinesh‐Kumar

Baker

2000

328

226

The N gene, a member of the Toll-IL-1 homology region-nucleotide binding site-leucine-rich repeat region (LRR) class of plant resistance genes, encodes two transcripts, N S and NL, via alternative splicing of the alternative exon present in the intron III. The NS transcript, predicted to encode the full-length N protein containing the Toll-IL-1 homology region, nucleotide binding site, and LRR, is more prevalent before and for 3 hr after tobacco mosaic virus (TMV) infection. The NL transcript, predicted to encode a truncated N protein (N tr ) lacking 13 of the 14 repeats of the LRR, is more prevalent 4 -8 hr after TMV infection. Plants harboring a cDNA-NS transgene, capable of encoding an N protein but not an N tr protein, fail to exhibit complete resistance to TMV. Transgenic plants containing a cDNA-NS-bearing intron III and containing 3 Ngenomic sequences, encoding both N S and NL transcripts, exhibit complete resistance to TMV. These results suggest that both N transcripts and presumably their encoded protein products are necessary to confer complete resistance to TMV.