The Poplar-Poplar Rust Interaction: Insights from Genomics and Transcriptomics
Stéphane Hacquard, Benjamin Petre, Pascal Frey, Arnaud Hecker, Nicolas Rouhier, and Sébastien Duplessis
Institut National de la Recherche Agronomique (INRA), Nancy Université, Unité Mixte de Recherche 1136, “Interactions Arbres/Micro-organismes,†Centre INRA de Nancy, 54280 Champenoux, France
Received 6 April 2011; Accepted 28 June 2011
Academic Editor: Brett Tyler
Copyright © 2011 Stéphane Hacquard et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Poplars are extensively cultivated worldwide, and their susceptibility to the leaf rust fungus Melampsora larici-populina leads to considerable damages in plantations. Despite a good knowledge of the poplar rust life cycle, and particularly the epidemics on poplar, the perennial status of the plant host and the obligate biotrophic lifestyle of the rust fungus are bottlenecks for molecular investigations. Following the completion of both M. larici-populina and Populus trichocarpa genome sequences, gene families involved in poplar resistance or in rust fungus virulence were investigated, allowing the identification of key genetic determinants likely controlling the outcome of the interaction. Specific expansions of resistance and defense-related genes in poplar indicate probable innovations in perennial species in relation with host-pathogen interactions. The genome of M. Larici-populina contains a strikingly high number of genes encoding small secreted proteins (SSPs) representing hundreds of candidate effectors. Transcriptome analyses of interacting partners in compatible and incompatible interactions revealed conserved set of genes involved in poplar defense reactions as well as timely regulated expression of SSP transcripts during host tissues colonisation. Ongoing functional studies of selected candidate effectors will be achieved mainly on the basis of recombinant protein purification and subsequent characterisation.
Acknowledgments
The authors would like to warmly thank all our colleagues at the Tree/Microbe Interactions Joint Unit at INRA and Nancy University for fruitful collaborations in the past years and numerous discussions on the concept of fungal effectors in tree-fungi interactions, particularly Francis Martin, Annegret Kohler, Emilie Tisserant, Valérie Legué, Claire Veneault-Fourrey, and Christine Delaruelle, who contributed to the recent poplar-poplar rust genomics and transcriptomics studies. They would like to also thank David Joly (currently postdoc in the Bakkeren lab, University of British Columbia, Canada) for his efforts in the annotation of M. larici-populina candidate effectors and Yao-Cheng Lin (postdoc at the Ghent VIB, Belgium) for the amazing amount of time dedicated to the analysis of the Melampsora genome. The authors also acknowledge their collaborators Armand Séguin and Hugo Germain at the Canadian Forest Service (Québec, Canada) for ongoing development of poplar rust effectors functional assays. Finally, the sequencing and annotation teams at the JGI are acknowledged for their everyday efforts in producing fungal genome sequences of such good quality. S. Hacquard and B. Petre contributed equally to this work.
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