Plant abiotic stress tolerance conferred by the desert endophytic bacterium Enterobacter sp. SA187 is mediated through enhanced ethylene signalling

Recent studies have shown that several plant species require microbial associations for stress tolerance and survival. In this work, we show that the desert endophytic bacterium Enterobacter sp. SA187 enhances yield and biomass of alfalfa in field trials, revealing a high potential for improving desert agriculture. To understand the underlying molecular mechanisms, we studied SA187 interaction with Arabidopsis thaliana. SA187 colonized surface and inner tissues of Arabidopsis roots and shoots and conferred tolerance to salt and osmotic stresses. Transcriptome, genetic and pharmacological studies revealed that the ethylene signaling pathway plays a key role in mediating SA187-triggered abiotic stress tolerance to plants. While plant ethylene production is not required, our data suggest that SA187 induces abiotic stress tolerance by bacterial production of 2-keto-4-methylthiobutyric acid (KMBA), known be converted into ethylene in planta. These results reveal a part of the complex molecular communication process during beneficial plant-microbe interactions and unravel an important role of ethylene in protecting plants under abiotic stress conditions. Overall design: 4 samples, 3 biological replicates Sterilized seeds were stratified for 3 days and then plated on ½ MS agar plates (Murashige and Skoog basal salts, Sigma), grown vertically for 5 days at 22 C and 16h light, then transferred to fresh ½ MS agar plates with (samples S, SB) or without (samples M, B) 100 mM NaCl (6 seedlings per plate) and cultivated for additional 12 days. Initial plates for sterilized seeds germination containing bacterial strain SA187 (2·10E+5 cfu·mL-1) were used to prepare samples B and SB. Control plates for samples M and S were non-inoculated.