SAR induction in tomato plants is not effective against root-knot nematode infection

Abstract

Systemic Acquired Resistance (SAR) is one of the defence mechanisms plants employee against pathogen attack, resulting in resistance and protection of distal tissues. It is characterized by the accumulation of salicylic acid (SA) and the expression of a group of pathogenesis-related (PR) genes; synthetic analogues of SA, such as INA and BTH, can induce SAR. The effects of INA and BTH on tomato plant development and on the tomatoMeloidogyne javanica interaction were investigated, and the response of both SAR and nematode pathogenesis to changes in the expression of several SA-responsive PR genes, PR-1b, PR-2 and PR-5, was determined. In addition, the response of calmodulin and PR-3 transcripts -two SA-independent genes -to SAR elicitor chemicals was also studied. All elicitortreated plants exhibited successful infestation by M. javanica, although a significant reduction of gall numbers was observed. INA was more efficient than BTH at inducing the SAR markers PR-1b and PR-2, but the root-knot nematode apparently suppressed the expression of these genes. This downregulation of gene expression following nematode infestation was also detected with regard to PR-3 expression. On the other hand, expression of PR-5 was not affected by elicitor treatment, though Meloidogyne infestation induced its expression.

Comparing systemic defence‐related gene expression changes upon migratory and sedentary nematode attack in rice

“…While down‐regulated in systemic shoots, in systemic root tissue (MgR) all PR genes ( OsPR1b , OsPR10 and OsPR1a ) were up‐regulated at both time points, suggesting activation of defence pathways in the roots. Our observations are remarkably similar to studies on PR gene expression in RKN‐infected Arabidopsis and tomato plants (Sanz‐Alferez et al. 2008; Hamamouch et al.…”

Variation in the response of tomato (Solanum lycopersicum) breeding lines to the effects of benzo (1,2,3) thiadiazole‐7‐carbothioic acid S‐methyl ester (BTH) on systemic acquired resistance and seed germination

“…However, Mandal et al. () and Sanz‐Alférez, Mateos, Alvarado, and Sánchez () found no up‐regulation following BTH application without pathogen infection in tomato ‘K326’ and ‘Marmande’, respectively. In this study, increased expression of SlPR1a was detectable for line 7024, but not line 7007 before Pst inoculation.…”

Not to be suppressed? Rethinking the host response at a root-parasite interface

“…The putative defense gene PR-1a is one example where failure to properly account for 14 developmental context could lead to misinterpretation. PR-1a was up-regulated systemically in leaves of tomato plants infested with root-knot nematodes, but there was no differential expression in root tissues [34]. While the absence of defense-related gene activation is sometimes taken as support for suppression of defense signaling, the PR-1a gene was not detectably expressed in roots treated with synthetic analogs of salicylic acid.…”

“…While the absence of defense-related gene activation is sometimes taken as support for suppression of defense signaling, the PR-1a gene was not detectably expressed in roots treated with synthetic analogs of salicylic acid. These treatments induced the expression of PR-1a in leaves, suggesting that the absence of gene induction in roots was not due to suppression but rather the irrelevance of this gene to the defense response within a root [34].…”

“…At the local site of invasion, salicylic acid levels that maintain the incompatible interaction provided by the Mi-1 resistance gene are important [33]. However, foliar pre-treatment of rice and tomato plants with salicylic acid analogs only slightly reduced susceptibility suggesting that the salicylate-mediated signaling may not have a major influence on root-knot nematode infestation of susceptible plants [25,33,34]. Conversely, foliar pre-treatments with jasmonates markedly reduced root-knot nematode infestation in both tomato and rice [25,35,36].…”