Physiological and transcriptome profiling analyses reveal important roles of Streptomyces rochei D74 in improving drought tolerance of Puccinellia distans (Jacq.) Parl

Drought is a major constraint for vegetation restoration of mine in arid areas. Actinomycetes exert positive roles in regulating growth and enhancing abiotic stress tolerance in plants. Nevertheless, the molecular mechanisms by which Actinomycetes improve the drought tolerance in Puccinellia distans remain mostly unknown. Here, the roles of Streptomyces rochei D74 (SR) on drought tolerance in Puccinellia distans grown under arid mining areas in situ were studied via physiological and transcriptome analysis. It turned out that SR treatment obviously increased the photosynthesis capacity of Puccinellia distans leaves by improving chlorophyll fluorescence (maximum efficiency of photosystem II, electron transport rate, quantum yield of photosystem II, and Non-photochemical quenching). SR also significantly enhanced the contents of soluble sugar and proline, thereby maintaining the osmotic adjustment of Puccinellia distans. In addition, SR alleviated reactive oxygen species damage by elevating the contents of glutathione, glutathione reductase and the activities of superoxide dismutase and peroxidase. RNA-Seq analysis identified 253 differentially expressed genes (DEGs) between SR-inoculated and non-inoculated Puccinellia distans leaves under drought. An in-depth analysis of these DEGs revealed that SR regulated the expression of genes related to photosynthesis (LHC, PsbR, FBP and RPE), sugar metabolism (EGLC, bglX, ENO and pyk), glutathione metabolism (DHAR, GST) and Ca2+ signal transduction (RBOH) under drought stress. Thus, SR inoculation improved Puccinellia distans growth and drought tolerance by regulating physiological and molecular characteristics of photosynthesis capacity, osmotic system and reducing reactive oxygen species damage. This study provides a theoretical basis for Actinomycetes in promoting the restoration of mine vegetation in arid areas.