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The International joint workshop on “PR-proteins” and “Induced resistance against pathogens and insects” was held in the Conference Centre “Zonheuvel” in Doorn, the Netherlands from May 10-14, 2007. The workshop was attended by over 150 delegates with research interests embracing basic and applied aspects of inducible resistance against pests and disease. There were 48 oral presentations and 75 posters covering a range of themes including PR-gene expression, signalling, priming, molecular ecology of induced resistance, and induced resistance for crop protection.
The first talk in the opening session was presented by Silvio Gianinazzi (INRA/CNRS, France) who discussed interactions between mycorrhizal fungi and PR-proteins in plant roots. Arbuscular mycorrhizal (AM) fungi form symbiotic associations with the root systems of many agronomically important plant species. The extent to which AM fungi regulate the expression of PR-genes, and that to which PRproteins limit root colonisation remains a subject of debate. It was suggested that localised induction of PR-proteins by AM fungi may prime both local and systemic resistance against subsequent attack by microbial pathogens. The signal associated with the AM-induced resistance response in the roots is unknown. Ted Turlings (University of Neuchatel) continued the ‘belowground’ theme with an elegant study describing the identification of a sesquiterpenoid signal that is emitted from maize roots that are under attack by larvae of Diabrotica virgifera virgifera. The signal molecule, (E)-a-caryophyllene, is an attractant for entomopathogenic nematodes which migrate to the damaged roots and infect the Diabrotica larvae. Interestingly, whilst European lines emit (E)-Ã¢-caryophyllene, the North American lines do not and it is suggested that this trait may have been lost during breeding. This represents a fascinating extension to the growing body of evidence supporting the importance of plant volatiles as signals for induced resistance and interplant communication.
Plants release volatile organic compounds (VOCs) in response to herbivore attack and these compounds attract parasites and predators to the attacking insect. Martin Heil (University of Duisburg-Essen, Germany) reported that VOCs from damaged Lima bean shoots can induce undamaged Lima bean plants to produce extrafloral nectar (EFN) which then attracts ants and other carnivorous arthropods. Furthermore, the VOC-treated plants are somehow ‘potentiated’ to secrete greater amounts of EFN in response to subsequent leaf damage. Thus, the VOCs operate as direct inducing agents and as priming agents. Priming of defences against fungal attack in Arabidopsis by chemical activators was discussed by Brigitte Mauch-Mani (University of Neuchatel, Switzerland), Jur ian Ton (Utrecht University, Netherlands) and Uwe Conrath (Aachen University, Germany). Although the phenomenon of priming has been known for many years, the underlying mechanisms are still largely unknown. Uwe Conrath reported that priming by benzothiadiazole was associated with the accumulation of ‘inactive’ MPK3 transcripts which became activated by phosphorylation upon pathogen challenge. Jurian Ton also reported an enhanced availability of transcription factors in plant cells primed by the nonprotein amino acid Ã-aminobutytic acid (BABA). Furthermore, the signalling pathways and defence mechanisms that were primed by BABA differed depending upon the nature of the challenging agent ie biotrophs (salicylic acid dependent) and oomycetes (abscisic acid dependent). It was proposed that priming may have a role in adaptive immunity so allowing plants to modulate their defences accordingly.
The final day of the Workshop began with presentations on the practical application of induced resistance for crop protection. Annegret Schmitt (BBA-IBP, Germany) described the regulatory processes involved for plant protection in Germany and referred interested parties to an information database on different products. Annegret set the scene nicely for my presentation on the integrated use of activators with biological control agents and traditional pesticides for crop protection in New Zealand. The programme then returned to more fundamental issues with Dan Klessig (Cornell, USA) discussing the role of salicylic acid binding proteins (SABPs) in the transmission of systemic signals. Dan presented a convincing argument that methyl salicylate is the long sought phloem mobile signal for SAR and that SABPs function by converting this compound to free salicylic acid in the systemic tissue.
The closing lecture was presented by Professor Kees van Loon (Utrecht University, Netherlands) who traced the history of PR-protein research from his pioneering studies as a PhD student in 1968 to the present day. In 1970, after some struggle for acceptance, van Loon & van Kammen published their research reporting changes in proteins in tobacco plants infected with tobacco mosaic virus. The rest, as they say is history! It must give great satisfaction to Professor van Loon to have watched PRprotein research become one of the most active research areas in plant biology, as evidenced by several thousand publications in the science literature. This was a fitting way to close a very informative and enjoyable workshop. I would like to thank the BSPP and HortResearch for financial support to attend the workshop. Thanks also to the organisers (Corne Pieterse, Kees van Loon and Marcel Dik) for providing the opportunity to make a presentation and for running such a well organised meeting.
Tony Reglinski HortResearch, New Zealand