Arbuscular mycorrhizal fungi modulate the leaf transcriptome of a Populus alba L. clone grown on a zinc and copper-contaminated soil

Significant improvement of growth associated with increased, rather than decreased, uptake of Cu and Zn has been observed in poplar plants inoculated with Glomus spp. as compared with non-mycorrhizal plants. The beneficial effect exerted by these arbuscular mycorrhizal fungi (AMF) is likely to be controlled by specific gene expression patterns in the plant. Until now, however, very little is known about the transcriptional changes which occur in response to heavy metals (HMs) in mycorrhizal vs. non-mycorrhizal poplar plants. In order to identify such HM- and/or AMF-induced changes in leaves of white poplar (Populus alba L.) plants grown, in the greenhouse, on Cu- and Zn-polluted soil, the cDNA-Amplified Fragment Length Polymorphism (AFLP) approach was adopted, resulting in the identification of a number of new differentially regulated genes. Transcript derived fragments (TDFs) mostly belonged to stress-related functional categories of defence and secondary metabolism. Genes belonging to different functional categories, plus other genes known to be related to HM stress (metallothioneins, phytochelatin synthase, glutathione synthase, arginine decarboxylase), were analysed by quantitative (q)RT-PCR. Transcript levels were generally down-regulated, or unaffected, in polluted soil compared with controls, the main exceptions being phytochelatin synthase and clathrin, and strongly up-regulated in the presence of AMF, especially Glomus mosseae.