Transcriptional reprogramming of the endophytic bacterium Enterobacter sp. SA187 upon Arabidopsis colonization

Enterobacter sp. SA187 is a plant growth-promoting bacterium (PGPB) that promotes growth of the crop plant alfalfa under saline irrigation and desert farming conditions. SA187 also enhances salt tolerance of the model plant Arabidopsis thaliana under in vitro conditions. In the present study, we used a transcriptomic approach to elucidate the mechanisms underlying plant growth promotion by SA187 under salt stress. Compared to free-living SA187, a massive metabolic reprogramming of SA187 occurs upon association with Arabidopsis. This effect was largely independent of the plant growth condition (non-salt or salt stress). Our data revealed pronounced changes in gene expression of proteins involved in cell signaling, chemotaxis, flagella biosynthesis, quorum sensing and biofilm formation. Also, upon plant interaction, a complete reprograming of nutrients acquisition and the central carbon metabolism of SA187 was observed. Moreover, in accordance with the previously identified role of bacterially produced 2-keto-4-methylthiobutyric acid (KMBA) in mediating salt stress tolerance, the sulfur metabolism of SA187 was strongly induced. Overall, our results give a deep insight into the metabolic and signaling pathways involved in the transition from free-living to a plant-associated PGPB life style of SA187. 4 samples, 3 biological replicates