Exploring the medicinally important secondary metabolites landscape through the lens of transcriptome data in fenugreek (Trigonella foenum graecum L.)

Abstract

Fenugreek (Trigonella foenum-graecum L.) is a self-pollinated leguminous crop belonging to the Fabaceae family. It is a multipurpose crop used as herb, spice, vegetable and forage. It is a traditional medicinal plant in India attributed with several nutritional and medicinal properties including antidiabetic and anticancer. We have performed a combined transcriptome assembly from RNA sequencing data derived from leaf, stem and root tissues. Around 209,831 transcripts were deciphered from the assembly of 92% completeness and an N50 of 1382 bases. Whilst secondary metabolites of medicinal value, such as trigonelline, diosgenin, 4-hydroxyisoleucine and quercetin, are distributed in several tissues, we report transcripts that bear sequence signatures of enzymes involved in the biosynthesis of such metabolites and are highly expressed in leaves, stem and roots. One of the antidiabetic alkaloid, trigonelline and its biosynthesising enzyme, is highly abundant in leaves. These findings are of value to nutritional and the pharmaceutical industry.

Figure 1

A snapshot of selected secondary metabolites produced by Trigonella foenum-graecum (shown in image is the AFG-1 variety). The abundance of these compounds make fenugreek a repertoire of nutraceutical and pharmaceutical properties.

Figure 2

Orthology analyses (A) OrthoMCL: Venn diagram representing the common and unique orthogroups for the five proteomes studied. (B) Proteinortho results showing the distribution of orthogroups between few selected plants from the subclass Rosids (including Arabidopsis thaliana and few plants from Faboideae and Rosaceae) and Oryza sativa. Each coloured section represents the number of species with which the orthogroups are shared.

Figure 3

Heatmap for top 20 most abundant transcripts (based on average TPM values) from leaf, stem and root tissues. The * sign indicates transcripts with multiple annotations. The annotation derived from the best hit have been ascribed for such transcripts.

Figure 4

Trigonelline biosynthesis pathway and relative abundance across tissues of the transcript encoding the enzyme-Nicotinate N-methyltransferase (represented as heatmap of average TPM value in log2 scale, in green-white colour scale). The pathway has been adapted from Plant Metabolic Network (PMN), https://pmn.plantcyc.org/PLANT/NEW-IMAGE?type=PATHWAY&object=PWY-5110&detail-level=3, on www.plantcyc.org, Aug 12, 2021.