Uncovering Alkaloid chemotype diversity in natural Festuca–Epichloë festucae symbioses across Iberian ecosystems

Abstract

Epichloë fungal endophytes are characterized by their biotrophic lifestyle and their highly specific and variable interaction with cool-season Pooideae grasses. These endophytes grow systemically in the apoplast of the aerial tissues and can reproduce sexually, asexually or interspersing both lifecycles. Within the cosmopolitan genus Festuca (Poaceae), Epichloë festucae is one of the most prevalent Epichloë endophytes, appearing in up to 30 taxa. This interaction has been thoroughly studied in agricultural species (e.g., Lolium perenne) due to the impact of endophyte-expressed secondary metabolites on farming and livestock production. To date, four alkaloid classes have been identified: ergot alkaloids, 1-aminopyrrolizidines (including lolines), indole-diterpenes and pyrrolopyrazines (including peramine), exhibiting toxicity or deterrence to vertebrates, insects or both.

Our study aimed to characterize the holobionts formed by five fine-leaved Festuca species (F. lambinonii, F. nigrescens, F. rubra subsp. pruinosa, F. yvesii, and F. rothmaleri) and their respective E. festucae strains across diverse Iberian ecosystems. Our specific objectives were: (1) to perform an integrative characterization of both symbionts using molecular, cytogenetic and morphological approaches; and (2) to quantitatively and qualitatively assess the chemotypes and conduct genetic screenings of endophytes in these holobionts.

We recorded a wide variety of chemotypes, finding differences between individuals at intra- and interspecific levels. For pyrrolopyrazines, peramine was detected in some individuals within the species F. yvesii and F. rothmaleri, whereas an alternative compound (pyrrolopyrazine 2a) was detected in the remaining individuals of these species and in all F. rubra subsp. pruinosa and F. lambinonii samples. For ergot alkaloids, only F. rubra subsp. pruinosa showed traces of chanoclavine and quantifiable ergovaline. Indole-diterpenes (e.g., paxilline, terpendole isomers, paspaline and 13-desoxypaxilline) were variably present in F. nigrescens, F. yvesii, and F. rothmaleri, whereas 1-aminopyrrolizidines were absent in all samples. Interestingly, results of the alkaloid analyses were not always consistent with the results of the genetic screens: in some cases, the genes of biosynthetic pathways were present, but the corresponding alkaloids were undetected.

Altogether, we were able to detect the presence of at least two alkaloid classes for all studied species, with exception of F. lambinonii, suggesting that the host species might obtain protection against invertebrates and, for those that produce certain ergovaline or certain indole-diterpenes, also against vertebrates. We believe that these findings evidence the importance of characterizing naturally distributed holobionts to expand our comprehension regarding the secondary metabolism associated with this symbiosis and the plasticity of E. festucae.