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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Upgrading Root Physiology for Stress Tolerance by Ectomycorrhizas: Insights from Metabolite and Transcriptional Profiling into Reprogramming for Stress Anticipation^{1,[C],[W],[OA]}

College of Life Sciences, Northwest Agriculture & Forestry University, Yangling, Shaanxi 712100, People's Republic of China (Z.-B.L.); Büsgen Institute, Department for Forest Botany and Tree Physiology (Z.-B.L., D.J., A.P.), and Albrecht-von-Haller Institute for Plant Sciences, Department for Plant Biochemistry (C.G., I.F.), Georg-August University, 37077 Goettingen, Germany; College of Life Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, People's Republic of China (X.J., Y.T.); and Institute of Forest Botany and Tree Physiology, Chair of Tree Physiology, Albert-Ludwigs University, 79110 Freiburg, Germany (H.W., H.R.)

Ectomycorrhizas (EMs) alleviate stress tolerance of host plants, but the underlying molecular mechanisms are unknown. To elucidate the basis of EM-induced physiological changes and their involvement in stress adaptation, we investigated metabolic and transcriptional profiles in EM and non-EM roots of gray poplar (Populus x canescens) in the presence and absence of osmotic stress imposed by excess salinity. Colonization with the ectomycorrhizal fungus Paxillus involutus increased root cell volumes, a response associated with carbohydrate accumulation. The stress-related hormones abscisic acid and salicylic acid were increased, whereas jasmonic acid and auxin were decreased in EM compared with non-EM roots. Auxin-responsive reporter plants showed that auxin decreased in the vascular system. The phytohormone changes in EMs are in contrast to those in arbuscular mycorrhizas, suggesting that EMs and arbuscular mycorrhizas recruit different signaling pathways to influence plant stress responses. Transcriptome analyses on a whole genome poplar microarray revealed activation of genes related to abiotic and biotic stress responses as well as of genes involved in vesicle trafficking and suppression of auxin-related pathways. Comparative transcriptome analysis indicated EM-related genes whose transcript abundances were independent of salt stress and a set of salt stress-related genes that were common to EM non-salt-stressed and non-EM salt-stressed plants. Salt-exposed EM roots showed stronger accumulation of myoinositol, abscisic acid, and salicylic acid and higher K⁺-to-Na⁺ ratio than stressed non-EM roots. In conclusion, EMs activated stress-related genes and signaling pathways, apparently leading to priming of pathways conferring abiotic stress tolerance.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Andrea Polle (apolle{at}gwdg.de).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.143735

^* Corresponding author; e-mail apolle{at}gwdg.de.

Received June 27, 2009; accepted October 4, 2009; published October 7, 2009.

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