Variability of Pyrrolizidine Alkaloid Occurrence in Species of the Grass Subfamily Pooideae (Poaceae).

Anne-Maria Wesseling,Karin Schwarz,Dietrich Ober,Tobias J Demetrowitsch

doi:10.3389/fpls.2017.02046

Abstract

Pyrrolizidine alkaloids (PAs) are a class of secondary metabolites found in various unrelated angiosperm lineages including cool-season grasses (Poaceae, subfamily Pooideae). Thesinine conjugates, saturated forms of PA that are regarded as non-toxic, have been described to occur in the two grass species Lolium perenne and Festuca arundinacea (Poaceae, subfamily Pooideae). In a wider screen, we tested various species of the Pooideae lineage, grown under controlled conditions, for their ability to produce thesinine conjugates or related structures. Using an LC-MS based targeted metabolomics approach we were able to show that PA biosynthesis in grasses is limited to a group of very closely related Pooideae species that produce a limited diversity of PA structures. High variability in PA levels was observed even between individuals of the same species. These individual accumulation patterns are discussed with respect to a possible function and evolution of this type of alkaloid.

Highlights

Pyrrolizidine alkaloids (PAs) are a typical class of plant secondary metabolites produced in various lineages of the flowering plants and their occurrence, structural diversity, and biosynthesis have been studied extensively for several decades (Hartmann and Witte, 1995; Stegelmeier et al, 1999; Ober and Kaltenegger, 2009)
The three PA-producing Lolium species, namely L. perenne, L. multiflorum, and L. rigidum, are outbreeders and have been shown to be closely related to each other (Catalán et al, 2004; Cheng et al, 2015). These outbreeding Lolium species present a sister group to the inbreeding Lolium species which include L. temulentum and L. remotum and which we have shown here to be PA-free
The presence of PAs in F. arundinacea is surprising considering their absence in F. pratensis

Summary

Introduction

Pyrrolizidine alkaloids (PAs) are a typical class of plant secondary (or specialized) metabolites produced in various lineages of the flowering plants and their occurrence, structural diversity, and biosynthesis have been studied extensively for several decades (Hartmann and Witte, 1995; Stegelmeier et al, 1999; Ober and Kaltenegger, 2009). The authors were able to show that, in the pasture grass species Lolium perenne and Festuca arundinacea, specific PA conjugates are detectable irrespective of fungal infection (Koulman et al, 2008) Structure elucidation revealed these compounds to be the stereoisomers E- and Z-thesinine in varying states of glycosylation. 1,2-saturated PAs such as thesinine found in the grasses are considered to be non-toxic (Hartmann and Witte, 1995) For this reason and the fact that these alkaloids accumulate in cultivars bred as pasture grasses to feed livestock, it was concluded that these compounds are not part of the plant’s chemical defense (Koulman et al, 2008). The biological function of these glycosylated grass PAs remains enigmatic

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Conclusion