Endophytic fungi and plant metabolomics

Fig 2 Final

The relationship between cool-season grasses and fungal endophytes is widely regarded as mutualistic, but there is growing uncertainty about whether changes in resource supply and environment benefit both organisms to a similar extent. In this work, we have been artificially infecting perennial ryegrass (Lolium perenne) cultivars  that differ in carbohydrate content, with different strains of Neotyphodium lolii (AR1, AR37, common strain) that differ intrinsically in alkaloid profile. We grow endophyte-free and infected plants under high and low nitrogen (N) supply and use quantitative PCR (qPCR) to estimate endophyte concentrations in harvested leaf tissues. 

So far we have found that endophyte concentration is reduced by 40% under high N supply, and by 50% in the higher sugar cultivar. These two effects seem to be additive (together resulting in 75% reduction). Alkaloid production is also reduced under both increased N supply and high sugar cultivar, and for three of the four alkaloids quantified, concentrations were linearly related to endophyte concentration.

We have also conducted a metabolomic analysis of 66 metabolic response variables. We found that at high N supply nitrogenous compounds, organic acids and lipids were increased; WSCs, chlorogenic acid (CGA) and fibres were decreased. The high sugar cultivar AberDove had reduced levels of nitrate, most minor amino acids (AAs), sulphur and fibres compared to the control cultivar Fennema, whereas WSCs, CGA, and methionine were increased. In plants infected with endophytes, nitrate, several AAs, and Mg were decreased; WSCs, lipids, some organic acids and CGA were increased. Re-growth of blades was stimulated at high N; and there was a significant endophyte x cultivar interaction on re-growth. Mannitol, a fungal specific sugar alcohol, was significantly correlated with fungal biomass.

Our findings suggest that effects of endophytes on metabolic profiles of L. perenne can be considerable, depending on host plant characteristics and nutrient supply, and we propose that a shift in C/N ratios and in secondary metabolite production as seen in our study is likely to have impacts on herbivore responses.  The results also stress the need for wider quantification of fungal endophytes in the grassland–foliar endophyte context, and have implications for how introducing new cultivars, novel endophytes or increasing N inputs affect the role of endophytes in grassland ecosystems.

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