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

Plant tolerance to stress is improved by mycorrhiza, but the underlying molecular processes remain to be elucidated. In this greenhouse study, Populus alba tolerant plants (clone AL35) were grown in pots containing either non-polluted soil (controls) or a copper and zinc-polluted soil; the latter plants were either pre-inoculated or not with an arbuscular mycorrhizal fungus (AMF): Glomus mosseae or G. intraradices. In order to evaluate the genome-wide changes occurring in the leaves, a cDNA-Amplified Fragment Length Polymorphism (AFLP) analysis was performed. The analysis showed that the transcriptome was strongly altered in plants grown on polluted soil relative to control plants and that it was further, and differentially, modulated by the two fungal species as compared with non mycorrhizal plants. 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. Leaf transcript levels of the considered genes 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 G. mosseae. Results are discussed in the light of previous ones showing that G. mosseae and G. intraradices are able to recover, entirely or partially, plant growth inhibition exerted by HMs, in spite of higher HM accumulation in plant organs.