Abstract
Plant growth promoting rhizobacteria (PGPR) hold promising future for sustainable agriculture. Here, we demonstrate a carotenoid producing halotolerant PGPR Dietzia natronolimnaea STR1 protecting wheat plants from salt stress by modulating the transcriptional machinery responsible for salinity tolerance in plants. The expression studies confirmed the involvement of ABA-signalling cascade, as TaABARE and TaOPR1 were upregulated in PGPR inoculated plants leading to induction of TaMYB and TaWRKY expression followed by stimulation of expression of a plethora of stress related genes. Enhanced expression of TaST, a salt stress-induced gene, associated with promoting salinity tolerance was observed in PGPR inoculated plants in comparison to uninoculated control plants. Expression of SOS pathway related genes (SOS1 and SOS4) was modulated in PGPR-applied wheat shoots and root systems. Tissue-specific responses of ion transporters TaNHX1, TaHAK, and TaHKT1, were observed in PGPR-inoculated plants. The enhanced gene expression of various antioxidant enzymes such as APX, MnSOD, CAT, POD, GPX and GR and higher proline content in PGPR-inoculated wheat plants contributed to increased tolerance to salinity stress. Overall, these results indicate that halotolerant PGPR-mediated salinity tolerance is a complex phenomenon that involves modulation of ABA-signalling, SOS pathway, ion transporters and antioxidant machinery.
Highlights
By the H+ -ATPase[6]
Plant growth promoting traits like phosphate solubilisation, indole acetic acid (IAA) production, nitrogen fixation and ACC deaminase activity were found to be negative in D. natronolimnaea STR1
Dietzia species have been reported to be associated with plants as endophytes[19] as well as with plant rhizomes growing in soda lakes[20]; limited information on their role in plant growth promotion exists[15]
Summary
By the H+ -ATPase[6]. Salinity alters the normal homeostasis of the cell and causes an increased production of reactive oxygen species (ROS)[7]. PGPR promote plant growth by altering the selectivity of Na+, K+, and Ca2+ and sustain a higher K+/Na+ ratio in plants under salt stress[11]. With significant improvements in our understanding of PGPR-mediated salinity tolerance in host plant, efforts are being made to understand the tolerance mechanism at the gene expression level. Transcriptomic analyses have been conducted for only a few rhizobacterial strains to unravel the changes in molecular mechanisms in plants associated with PGPR-mediated plant growth promotion[13,14]. With the aim of understanding the possible mechanisms involved in PGPR-mediated salinity tolerance in wheat plants, we studied the expression of different genes involved in salt stress tolerance in plants
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