The Genome of Undifilum oxytropis Provides Insights into Swainsonine Biosynthesis and Locoism.

Hao Lu,Haiyun Quan,Zhenhui Ren,Shuai Wang,Baoyu Zhao,Ruixu Xue

doi:10.1038/srep30760

Hao Lu, Haiyun Quan + Show 4 more

Open Access

https://doi.org/10.1038/srep30760

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Abstract

Undifilum oxytropis is a fungal endophyte of locoweeds. It produces swainsonine, which is the principal toxic ingredient of locoweeds. However, the genes, pathways and mechanisms of swainsonine biosynthesis are not known. In this study, the genome of U. oxytropis was firstly sequenced and assembled into a 70.05 megabases (Mb) draft genome, which encoded 11,057 protein-coding genes, and 54% of them were similar to current publicly available sequences. U. oxytropis genes were annotated and 164 putative genes were annotated into enzymes, such as Saccharopine dehydrogenase, Saccharopine oxidase, and Pyrroline-5-carboxylate reductase, hypothesized to be involved in the biosynthesis pathway of swainsonine. The genome sequence and gene annotation of U. oxytropis will provide new insights into functional analyses. The characterization of genes in swainsonine biosynthesis will greatly facilitate locoweed poisoning research and help direct locoism management.

Highlights

Locoweeds are poisonous legumes that belong to the genera Oxytropis and Astragalus
We knew that swainsonine is a final product of L-lysine degradation, from L-Lysine to Saccharopine and L-2-aminoadipate 6-semialdehyde, the two intermediates can be obtained from L-lysine degradation (KEGG map00310), from the genome annotation results, and we found that 5 genes was annotated to a key enzyme, Saccharopine dehydrogenase (SDH, EC:1.5.1.-) of this pathway
In L-Lysine degradation process, from L-2-aminoadipate 6-semialdehyde to ∆1-piperideine-6-carboxylic acid (P6C), 1 gene was annotated to Saccharopine oxidase (FAP2, EC 1.5.3.1), we found 2 genes annotated to pyrroline-5-carboxylate reductase (P5CR, EC:1.5.1.2) from P6C to L-pipecolate

Summary

Introduction

Locoweeds are poisonous legumes that belong to the genera Oxytropis and Astragalus After ingesting these toxic plants, livestock can develop diseases characterised by chronic dysfunction of the nervous system[1,2,3]. Undifilum species have been found to be associated with swainsonine-containing Astragalus and Oxytropis species in China and North America[19,23,24] In these plants, swainsonine levels were correlated positively with U. oxytropis content[25], which provided original evidence that fungal genetics might play an important role in swainsonine production[20]. This study will further contribute to the understanding of the biosynthesis pathway and metabolic mechanism of swainsonine, and provide an important reference for prevention and treatment of locoweed poisoning in livestock

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