Foliar Epichloë fungal endophytes affect soil biochemistry via changes in the expression of root genes and exudates...

Soils are reservoirs of key nutrients and enzymes for plant fitness and ecosystem productivity. Epichloë fungal endophytes are well-known to shape plant performance, yet the mechanistic link between Epichloë-mediated changes on plant root genes and root exudates with soil biochemistry is not entirely clear. We studied the effect of the foliar endophyte Epichloë gansuensis (C.J. Li & Nan) on the soil biochemistry and composition/abundance of host root genes and exudates. We hypothesized that Epichloë would affect soil biochemistry, and that these changes would be associated with endophyte-mediated alterations in root genes and exudates.

Soil samples, root tissues and root exudates were harvested from field plots of Achnatherum inebrians (Hance) Keng plants with and without E. gansuensis endophytes. We measured concentrations/activities of nutrients/enzymes in bulk and rhizosphere soils, together with the composition and expression of root genes and exudates that were determined via high-resolution liquid chromatography-mass spectrometry and RNA-sequencing.

Epichloë altered concentrations/activities of several nutrients/enzymes in both soil compartments (e.g. organic carbon, β-glucosidase), with larger effects in the rhizosphere soil than bulk soil. Epichloë also modified the expression of root genes (e.g. AHCY) and exudates (e.g. malate, ethylene), with several of the changes in root exudates aligned with the altered expression of root genes (e.g. high malate abundance was associated with enhanced expression of its biosynthesis genes). Many of the Epichloë-derived changes in soil nutrients and enzyme levels were functionally associated with the release by the host plant of bioactive root exudates affected by the endophyte.

Foliar Epichloë endophytes can shape soil biochemistry, root gene expression and root exudate abundance, and the existence of functional links between soil biochemistry and root exudates in plant-endophyte associations.