The indole-alkaloid Gramine shapes the bacterial communities thriving at the barley root-soil interface. Barley_gramine

The biosynthesis of plant allelochemicals underpinning inter-organismal relationships has been moulded by domestication and breeding selection. The indole-alkaloid gramine, whose occurrence in the staple crop Barley (Hordeum vulgare L.) is widespread among wild genotypes but virtually absent from modern varieties, is a paradigmatic example of this phenomenon. This prompted us to investigate how the exogenous application of gramine impacted on the rhizosphere bacterial microbiota of two modern barley genotypes grown in a reference agricultural soil. Using an Illumina amplicon sequencing survey, we demonstrated that gramine partitioned the bacterial composition of both unplanted soil and rhizosphere specimens. This effect is two-pronged: a component of the barley microbiota responds to gramine application in a genotype- and dosage-independent manner while at the highest dosage the host genotype further regulates the impact of this secondary metabolite on rhizosphere communities. These initial observations indicate that gramine can act as a determinant of the bacterial communities inhabiting the root-soil interface.