Published by Oxford University Press [2006] on behalf of the Society for Experimental Biology.
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Preface to Phloem–Insect Interaction
The review articles presented here were invited from keynote speakers at the session on Phloem–Insect Interaction at the Society for Experimental Biology (SEB) Annual Meeting in Barcelona, Spain 2005. The session was generously supported by the SEB, the Journal of Experimental Botany, and Syngenta.
The interaction between sap-feeding herbivores (such as aphids) and plants is unusual since it is dominated by a single plant cell type, the phloem sieve element. The aim of the session was to present current knowledge of the physiology and behaviour of phloem-feeding insect herbivores as well as the physiology, biochemistry, and molecular biology of the phloem. A major objective was to facilitate the integration of these very different areas to encourage new initiatives to move our understanding forward. Recent advances in molecular techniques, including the proteomics and transcriptomics tools, are central to this aim. Conversely, these powerful analytical tools can not be used without a sound understanding of the underlying physiology.
The five key review papers presented here span the whole area of plant–insect interaction, from the ecological to the molecular. It is hoped that they will provide a useful resource to help define and move forward this exciting area.
The first paper by Will and van Bel introduces the physiology of the phloem and the role of the novel forisome proteins in sealing the sieve tubes. Combining plant physiology with insect behaviour provided tantalizing suggestions that the aphid interaction with these proteins may explain the success or failure of sap-feeding insects on their host plants. Understanding these interactions with high spatial and temporal detail is essential to link herbivore behaviour with plant response. The electronic penetration graph (EPG) technique provides this resolution and, in the second paper, Professor Tjallingii discusses the use of EPG in unravelling the stylet–sieve element interaction and highlights current understanding of the role of aphid saliva in overcoming plant defences. In the third paper, Professor Douglas considers the plant–insect interaction from the point of view of the aphid where the sieve element sap is considered as the insect diet. Central to the suitability of sieve element sap as diet is the role of the aphid bacterial symbiont Buchnera in modifying sap composition. Revealing the interaction as tri-trophic underlines the complexity of the plant–herbivore relationship. The final two papers explore the potential impact of the new 'omics technologies in understanding the plant–insect interaction. In a paper considering the emerging transcriptomics data, Goggin and Thompson outline the genes that are currently thought to alter expression during aphid feeding and assign these to a variety of plant responses, including direct defence and signalling pathways. Further technological refinements in these approaches will permit greater focus on the response of the sieve element, allowing the earliest plant responses to be observed. Current knowledge of the phloem proteome is explored in the final paper, in which Kehr explores the technical and practical difficulties of using these powerful techniques on a single cell type. The applied aspects of exploiting the specific interaction of sap-feeding pests with plants is outlined and it is clear that analysis of the plant proteome is still in its infancy, but promises much.
These five papers define the current state of knowledge in the area. An increasing amount of data is appearing and the need for standardization in both experimental design and bioinformatics analysis is essential. The picture presented here is the result of many different biological areas and expertise. The final piece of the jigsaw will be in place when the aphid genome sequencing projects begin to produce complementary information from the side of the insect. The study of plant–insect interaction has many interesting questions on both sides and continued integration of different biological areas, coupled with emerging analytical tools, will rapidly increasing our understanding of this important ecological interaction and, potentially, will provide novel control strategies for this important pest guild.
Thanks are due to the Editorial Office staff of the Journal of Experimental Botany (Mary Traynor, Jane Basterfield, Diana Kitching, and Raquel Gonzalez-Cuesta) and also to Chris Trimmer at the SEB for her help in organizing the Barcelona session. Their guidance and support has been much appreciated.
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