Metatranscriptomics of pastures under drought stress show a rhizospheric meta-organism reshape

Abstract

Rhizosphere interactions represent a new and relevant perspective in the study of drought resistance mechanisms in agricultural and livestock forage production, considering the reduced water availability exacerbated by climate change. In this mesocosm study, drought-induced stress was evaluated in three Poaceae species (Lolium arundinaceum (Schreb.) Darbysh., Oloptum miliaceum (L.), Röser & Hamasha, Dactylis glomerata L.). Stress marker activities (Lipid Peroxidation, Phenylalanine Ammonia Lyase, Proline content and Glutathione S-Transferase), antioxidant enzyme activities (Guaiacol Peroxidase, Ascorbate Peroxidase, Catalase, Superoxide Dismutase), photosynthetic pigment content were tested on plant samples. The results showed an increased stress and a decline in photosynthetic efficiency following the drought stress. The rhizosphere metatranscriptome analysis revealed taxonomic and functional expression shift. Proteobacteria and Bacteroides abundance increased under stress (from 36% to 4%–48% and 7%, respectively). Contrariwise, Actinobacteria decreased from 6% to 2%. Most of the up-regulated transcripts in the stressed samples fall into GO biological classes such as response to stress (GO:0006950), oxidative stress (GO:0006979), response to heat (GO: 0009408), and osmotic stress (GO:0071,470) and were mainly expressed by Burkholderiales and Rhodospirillales. In line with the proline increase in stressed plants, an up-expression of all transcripts involved in proline biosynthesis was also found at the rhizospheric level, confirming the rhizospheric metaorganism synergic action.