Rethinking of the Roles of Endophyte Symbiosis and Mycotoxin in Oxytropis Plants

Abstract

Plants in the Oxytropis genus can live with the endophytic fungi Alternaria sect. Undifilum. Swainsonine, the mycotoxin produced by the endophyte render the host plant toxic and this has been detrimental to grazing livestock in both China and U.S.A. Despite previous efforts, many questions remain to be solved, such as the transmission mode and life cycle of host–endophyte symbiont, the biosynthesis pathway of swainsonine, and in particular the ecological role and evolution of such symbiosis. In this review, we compile the literature to synthesize ideas on the diversity of the symbiosis and propagation of the endophyte. We further compare the previous work from both Alternaria sect. Undifilum and other swainsonine producing fungi to orchestrate a more comprehensive biosynthesis pathway of swainsonine. We also connect swainsonine biosynthesis pathway with that of its precursor, lysine, and link this to a potential role in modulating plant stress response. Based on this we hypothesize that this host–endophyte co-evolution originated from the needs for host plant to adapt for stress. Validation of this hypothesis will depend on future research on endophytic symbiosis in Oxytropis and help in better understanding the roles of plant–endophyte symbiosis in non-Poaceae species.

Assembly of high‐quality genomes of the locoweed Oxytropis ochrocephala and its endophyte Alternaria oxytropis provides new evidence for their symbiotic relationship and swainsonine biosynthesis

“…given PA is the precursor of swainsonine and is the direct substrate to be catalysed by SWN (Guan et al, 2021). The other two peptides, including AASADH and PIPOX found in R. leguminicola, related in the lysine metabolic pathway (Li et al, 2012), were also found in the genome of A. oxytropis.…”

“…The A. oxytropis genome improved our understanding on the biosynthetic pathway of swainsonine. Swainsonine biosynthesis was suggested as a result of lysine metabolism via PA as an intermediate (Guan et al, 2021). Although swainsonine can only be produced by a limited number of fungal species, PA is a ubiquitous metabolite in plants, bacteria and fungi (Arruda & Barreto, 2020), in which versatile biosynthesis pathways have been suggested for PA (Neshich et al, 2013).…”

“…A. oxytropis was isolated and cultured from the seed coat of O. ochrocephala on potato dextrose agar (PDA). Its identity was confirmed by ITS sequencing before it was subjected to whole genome sequencing (Guan et al, 2021). High-quality genomic DNA samples of plants and fungi were extracted by the cetyltrimethyl ammonium bromide (CTAB) method.…”

“…The A. oxytropis genome was analysed to consider mechanisms of swainsonine biosynthesis (for a schematic of swainsonine biosynthesis, see review by Guan et al, 2021). Based on our data the following genes involved in the swainsonine biosynthesis pathway Figure 5a; Table S27).…”

Fungal Endophytes of Vitis vinifera—Plant Growth Promoters or Potentially Toxinogenic Agents?

“…Generally, the presence of mycotoxins in agricultural crops and exposure to consumers is a global problem carrying substantial and widespread threats to health [12]. Contrary to other plants, where the toxinogenic potential of fungal endophytes have been studied (predominantly leaf vegetable [13], legumes [14] or different grasses and plants potentially toxic for grazing livestock [15][16][17]), in the case of V. vinifera, this important aspect of grapevine endomicrobiota remained unstudied.…”