The root fungal endophyte Piriformospora indica promotes the growth and survival of plants belonging to a number of species when exposed to various abiotic stresses, including drought, a major constraint of crop productivity. The application of 'omics technologies has revealed much of the molecular basis of the plant drought stress response. Here, the proteomic and metabolomic response of the leaves of moisture-stressed barley plants inoculated with P. indica was characterized. The abundance of 145 proteins was altered by the imposition of moderate drought on plants inoculated by P. indica, as was that of 104 in non-inoculated plants, while an episode of more severe stress altered the content of, respectively, 144 and 462 proteins. Many of these responsive proteins were involved in the plant’s primary metabolism, in particular acting to mitigate the damage caused by oxidative stress. Colonization of the roots by P. indica enhanced the activity of both the photosystem and the electron transfer chain, and also promoted the accumulation of proteins protective of photorespiration, energy modulation, primary metabolism, transporters and autophagy. The beneficial effect of P. indica colonization on autophagy in plants exposed to stress may relate to alterations in the host’s amino acid metabolism.
