MODULATION OF BARLEY (Hordeum vulgare) DEFENSE AND HORMONAL PATHWAYS BY PSEUDOMONAS SPECIES ACCOUNTED FOR SALINITY TOLERANCE

In the present study, we investigated two Pseudomonasspecies strains (P. fluorescens SBW25 and P. putida KT2440) for their use in plant tolerance under salt stressed condition. Barley (Hordeum vulgare L.) plants inoculated with PGPR strains were subjected to 200mM salinity stress and were analyzed in comparison to non-treated stressed plants based on height, leaf area and fresh and dry weights of shoots. Our data revealed significant enhancement of root fresh and dry weights, chlorophyll content and relative water content in PGPR applied plants. Further investigation of various phytohormones (ABA, JA, ethylene, SA and IAA), stress responsive transporters and antioxidant enzymes genes at molecular level revealed that among the selected genes of ABA biosynthesis and regulated genes including NCED, DHN5, DRF1and WRKY18 were significantly down-regulated, while P5CS1 and DHN1 genes weresignificantlyup-regulated by PGPR applications. Except LOX2 all the selected genes (FAD3, LOX1, AOS, AOC, OPR3, PLD alpha 1 and PI (SD10)) of JA biosynthesis pathway were significantly up-regulated by P. putida KT2440 strain. KT2440 strain also significantly induced the expression of ethylene biosynthesis ACCO and ACCS and SA biosynthesis ICS and protein kinase MAPKK genes. For auxin pathway, P. fluorescens SBW25 strain helped in significant induction of TDC expression, while P. putida KT2440 strain significantly boosted the expression of T5M gene. Both PGPR strains, displayed significant down-regulation of NHX1 antiporter, while showed an up-regulation of GR antioxidant gene. A significant enhanced expression of nitrate transporter NRT2.2, and antioxidant CAT2 genes was observed in P. fluorescens SBW25 inoculated barley roots compared to control roots. The findings of our study revealed effectiveness of selected PGPR strains for enhancing salinity tolerance by modulating the expression of major defense mediated pathways, stress responsive transporters and of antioxidant enzymes genes. Both PGPR strains showed improved effects, but P. putida KT2440 showed more pronounced significant effects comparatively. Conclusively, these PGPR species are an effective source of plant stress tolerance and elevated growth of barley plants.