Mutualistic plant microbe interactions in Nicotiana attenuata : from bacterial communities to single players Endosphere inhabiting mutualistic bacteria establish intimate relationships with their host plant and often provide services like plant growth promotion (PGP) or disease protection. How plants select for these microbes and which mechanism of PGP are employed remain mostly elusive. I assessed the relevance of plant ethylene (ET) signaling in the recruitment of culturable mutualistic bacteria to the root endosphere of the wild tobacco species Nicotiana attenuata. Wild type (WT) and transgenic lines either deficient in ET biosynthesis (ir aco1) or ET perception (35S etr1) grown in native soils were employed. The bacterial diversity of N. attenuata’s was strongly determined by the soil type and to a lesser extent by plant ET signaling. In terms of PGP about 50% of the isolated strains conferred positive effects on seedling growth. ...