Aluminum (Al) toxicity has been considered as an important factor in limiting the growth and nutrient acquisition of forest trees in acidic soils. Mycorrhizal fungi particularly ectomycorrhiza (ECM) may offset negative impacts of Al in root zone. Ectomycorrhizas (EMs) alleviate stress tolerance of trees, but the underlying molecular mechanisms are unknown. To elucidate the basis of EM-induced physiological changes and their involvement in stress adaptation, we investigated genome-wide transcriptional profiles and limited metabolite analysis in EM and non-EM roots of poplar (Populus trichocarpa) in the presence of aluminum stress. Mycorrhizal and nonmycorrhizal plants were exposed to Al levels of 0, 50 and 500µM.

Results/Conclusions

The biomass of mycorrhizal plant increased significantly as compared to nonmycorrhizal plants. The roots and shoots of mycorrhizal plants showed higher levels of mineral nutrient such as phosphorous and calcium compared to nonmycorrhizal plants. The Al stress-related organic acids increased, whereas sugars were decreased in mycorrhizal roots as compared with non-mycorrhizal roots, but  no significant difference observed in sugars and organic acids content in shoots of mycorrhizal  and nonmycorrhizal plants suggesting tissue specific stress adaptation in presence of EM. 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 aluminum stress and a set of aluminum stress-related genes that were common to EM non-Al-stressed and non-EM aluminum-stressed plants. Aluminum-exposed EM roots showed stronger upregulation of genes involved in ascorbate-glutathione pathway and phospholipase signaling. In conclusion, EMs activated stress-related genes and signaling pathways, apparently leading to priming of pathways conferring Al stress tolerance.