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The workshop was held at the University of Neuchâtel, was attended by over 170 delegates and included sessions focussing on defence signalling, crosstalk, priming, molecular ecology and practical aspects of induced resistance for crop protection. In the opening session, Roberto Solano (Centro Nacional de Biotecnologia, Madrid) proposed that the specificity of plant responses regulated by Jasmonate -Isoleucine may be co-ordinated via differences in the expression patterns of mostly redundant transcription factors (TFs) rather than by specific interactions between JAZ proteins and their respective TF targets. Corne Pieterse’s (Utrecht University) talk on ‘making sense out of signalling during plant defence’ described how regulation of the jasmonic acid (JA) signalling pathway occurs via antagonism between the ERF and MYC2-type TFs.
Insect larvae (Pieris rapae) prefer feeding on arabidopsis genotypes in which the ERF-branch is activated and, furthermore, larval oral secretions stimulate the ERF-branch of the JA pathway. It was suggested that plants could be made less attractive to herbivory by stimulating the naturally antagonistic MYC2-branch and hence preventing activation of the ERF branch. Crosstalk between signalling pathways play an important role in the coordination of plant resistance and the interact ions between individual hormonal networks are becoming ever more complicated.
The role of salicylic acid (SA) in the activation of systemic acquired resistance (SAR) has remained a focus for plant defence research for over two decades. It was appropriate therefore that an eminent scientist in this field, Dan Klessig (Boyce Thompson Institute for Plant Research, USA) described the interrelationships among SA, methyl salicylate (MeSA) and light in the establishment of SAR. Previously, Klessig’s lab reported that MeSA is an essential mobile signal in the establishment of systemic acquired resistance (SAR), however this was recently countered by Attaran et al. In his presentation, Dan described how these apparently conflicting results may be due to differences in experimental design and, more specifically, to the duration of light following the initial inducing event. The light period affects subsequent methylation and demethylation of SA and so determines whether MeSA is involved or whether it plays only an auxiliary role. MeSA was required for establishment of SAR only when plants were exposed to light for less than 3. 5h after induction. This highlighted the importance of experimental design and to be mindful of biotic and abiotic factors when interpreting the plant defence response.
Fumiaki Katagiri (University of Minnesota) described how signalling networks involved in pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) may interact to coordinate the plant response. PTI and ETI extensively share the same signalling machinery but the interactions occurring within the respective signalling networks differ. There is synergy among signalling networks in PTI whereas in ETI secondary sectors can act as a backup when primary sectors are impaired. For example many SA-responsive genes can be regulated in an SA-independent manner during ETI. It is argued that the robustness of ETI is based upon this ability to compensate when particular sectors have been perturbed.
A session on “The future of induced resistance” included papers by Jurian Ton (University of Sheffield) and Estrel la Luna-Diez (Rothamsted Research) who presented evidence for transgenerational SAR. Estrella found that progeny (S1) from pathogen stressed (Pseudomonas syringae pv tomato DC3000) arabidopsis were primed for activation of SA-inducible genes and were more resistant to biotrophic infection than the progeny of mock-inoculated arabidopsis. However, the S1 plants also exhibited reduced responsiveness to JA and enhanced susceptibility to necrotrophic fungi. Transgenerational SAR persisted into the second generation and was dependent upon the regulatory protein NPR1. Transmission of SAR to subsequent generations is proposed to involve DNA methylation and also posttranslational histone modifications at promoters of SA and JA-inducible genes. The ‘heritability’ of induced resistance represents a new and extremely exciting area of research that will be fascinating to follow over the coming years.
This was a thoroughly enjoyable, stimulating and extremely well organised meeting in a very picturesque setting on the banks of Lake Neuchâtel. The old town of Neuchâtel had a wonderful atmosphere and this added to the overall experience. I thank BSPP for the travel award and so making my attendance possible.
Plant and Food Research, New Zealand