Abstract
Oxytropis plants are widely distributed in the grasslands in northern China. Some Oxytropis species have been reported to contain the mycotoxin swainsonine, an alkaloid which causes poisoning in livestock, referred to as locoism. Previous studies showed that endophytic fungi (Alternaria oxytropis) symbiotically associate with these Oxytropis species to produce swainsonine. However, the influence of variation within the Oxytropis genus on the fixation or loss of symbiosis and toxicity is poorly understood, as is the influence of environmental factors. Here we used a collection of 17 common Oxytropis species sampled in northern China to assess genetic diversity using genotyping by sequencing which was compared with the levels of the endophyte and swainsonine. Results showed that nine Oxytropis species have detectable A. oxytropis colonisation, and seven Oxytropis species contain sufficient swainsonine to be considered poisonous, whereas the rest may be non-toxic. Species variation rather than the genetic lineage was associated with the fixation or loss of endophyte and swainsonine production, which appears to have resulted from genetic drift. Genotype × Environment (G × E) effects were also found to influence endophyte and swainsonine levels amongst species of the Oxytropis genus. Our study will provide a better understanding about the evolutionary basis of A. oxytropis symbiosis and swainsonine biosynthesis in locoweeds.
Highlights
The symbiosis between plants and endophytic fungi is common in nature [1–3], and the fungi have beneficial, neutral or detrimental effects to the host plants
By determining the endophyte and swainsonine levels, we considered whether genetic lineage within the genus could be related to the colonisation of A. oxytropis and swainsonine biosynthesis
The results of our study suggested A. oxytropis symbiosis and swainsonine biosynthesis in Oxytropis may be influenced by G × E effects
Summary
The symbiosis between plants and endophytic fungi is common in nature [1–3], and the fungi have beneficial, neutral or detrimental effects to the host plants. Some hosts exhibit a preference for certain endophytic fungal interactions [4]. The diversity and distribution of endophytes across biomes and their effects on plant phylogeny and host tissues have attracted considerable attention [5]. Some Oxytropis species form a symbiotic interaction with the endophytic fungi Alternaria Undifilum) oxytropis, to synthesise a mycotoxin, swainsonine [8–10]. Poisonous Oxytropis species can become dominant in the plant community, as observed in many grasslands in China [16]. Understanding what can influence mycotoxin production in the Oxytropis–A. oxytropis symbiont is of considerable importance, to reduce the risk of livestock poisoning, and to improve our knowledge of key aspects of host–endophyte symbiosis
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