Abstract
The corm of Hypoxis hemerocallidea, commonly known as the African potato, is used in traditional medicine to treat several medical conditions such as urinary infections, benign prostate hyperplasia, inflammatory conditions and testicular tumours. The metabolites contributing to the medicinal properties of H. hemerocallidea have been identified in several studies and, more recently, the active terpenoids of the plant were profiled. However, the biosynthetic pathways and the enzymes involved in the production of the terpene metabolites in H. hemerocallidea have not been characterised at a transcriptomic or proteomic level. In this study, total RNA extracted from the corm, leaf and flower tissues of H. hemerocallidea was sequenced on the Illumina HiSeq 2500 platform. A total of 143,549 transcripts were assembled de novo using Trinity and 107,131 transcripts were functionally annotated using the nr, GO, COG, KEGG and SWISS-PROT databases. Additionally, the proteome of the three tissues were sequenced using LC-MS/MS, revealing aspects of secondary metabolism and serving as data validation for the transcriptome. Functional annotation led to the identification of numerous terpene synthases such as nerolidol synthase, germacrene D synthase, and cycloartenol synthase amongst others. Annotations also revealed a transcript encoding the terpene synthase phytoalexin momilactone A synthase. Differential expression analysis using edgeR identified 946 transcripts differentially expressed between the three tissues and revealed that the leaf upregulates linalool synthase compared to the corm and the flower tissues. The transcriptome as well as the proteome of Hypoxis hemerocallidea presented here provide a foundation for future research.
Highlights
The term African potato refers to the tuberous rhizome of the herbaceous plant species belonging to the Hypoxidaceae family
RNA extracted from the corm, leaf and flower of H. hemerocallidea was sequenced on the Illumina Hi-Seq 2500 platform to generate the first de novo transcriptome of the phytomedicinal plant
After trimming the raw reads with Trimmomatic, more than 97% of the reads had a Phred score larger than 30 where base read accuracy is at 99.9% (S1 Fig)
Summary
The term African potato refers to the tuberous rhizome of the herbaceous plant species belonging to the Hypoxidaceae family. One of the more popular species is Hypoxis hemerocallidea. The rhizomes of Hypoxis spp. are used in traditional medicine to treat several illnesses such as urinary infections, inflammatory conditions, hypertension, testicular tumours, some cancers, and HIV-AIDS [2]. Having attracted sufficient attention for its medicinal properties, in 1969 a hydroalcoholic extract from H. hemerocallidea was patented for anti-inflammatory, antibiotic, anti-arthritic, anti-atherosclerotic and diuretic properties, as well as a stimulant of muscular and hormonal activities [3]. Aqueous and methanolic extracts showed anti-inflammatory effects in rats with induced edema in the paw by subplantar injections with fresh egg albumin [4]. Aqueous extracts were found to have antinociceptive properties, antidiabetic properties [5, 6] and delayed the onset of seizures induced with pentylenetetrazole (PTZ)
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