Karyotype analyses of ten sections of Trigonella (Fabaceae)

Variability in genome size of Trigonella foenum-graecum, Trigonella corniculata and Trigonella caerulea as estimated by flow cytometry indicates complex evolutionary history of fenugreek

BACKGROUND

The determination of genome size is a fundamental step which provides a basis to initiate studies aimed at deciphering the genetic similarity of a species and to carry out other genomics based investigations. Fenugreek (Trigonella spp.) is an important spice crop which has numerous health promoting phytochemicals. Many species within this genus are known for their various health benefits owing to the presence of a wide diversity of important phytochemicals like diosgenin, trigonelline, fenugreekine, galactomannan, 4-hydroxy isoleucine, etc. It is a multipurpose crop being cultivated for food, animal feed and industrial purposes. Despite its importance, research on the genomics aspect of fenugreek remains scant. In the absence of sufficient genomic information, crop improvement in fenugreek is severely lagging.

METHODS AND RESULTS

Estimation of genome size of a species is the preliminary step for initiation of any genomic studies and therefore in the present study we have estimated the genome size for fenugreek. Here, we have determined the genome sizes of three different Trigonella spp. namely T. foenum-graecum, T. corniculata and T. caerulea through flow cytometry (FC). The 2 C DNA content values were found to be 6.05 pg (T. foenum-graecum), 1.83 pg (T. corniculata) and 1.96 pg (T. caerulea). The genome size of T. foenum-graecum is approximately three times the genome size of T. corniculata and T. caerulea. This variation in genome size of more than three-fold indicates the level of genetic divergence among the three species, though within the same genus.

CONCLUSIONS

The differences observed in the genome sizes of the three species provide conclusive evidence of their genetic divergence. Additionally, the information about the genome size would provide an impetus to the structural and functional genomics-based research in this crop.

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

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.

Five Fabaceae Karyotype and Phylogenetic Relationship Analysis Based on Oligo-FISH for 5S rDNA and (AG3T3)3

Most Fabaceae have nitrogen fixation abilities and are valuable forage and medicinal resources. However, cytogenetic data of many Fabaceae species are unclear. Karyotypes reveal cytological characteristics and are crucial to understanding the organization and evolution of chromosomes in species. Oligo-FISH can reveal genetic composition and karyotype variation patterns with rapid and efficient results. Karyotype analysis of five Fabaceae species by oligonucleotide probes showed that: Robinia pseudoacacia, karyotype formula 2n = 2x = 20m + 2sm, cytotype 2B, arm ratio 3.4821, eight chromosomes distributed 5S rDNA signal. The karyotype formula of Robinia pseudoacacia ‘idaho’ was 2n = 2x = 20m + 2sm, cytotype 1A, arm ratio 1.8997, and 5S rDNA signal was distributed on six chromosomes. Karyotype of Robinia pseudoacacia f. decaisneana 2n = 2x = 20m + 2sm, cytotype 1B, arm ratio 2.0787, the distribution of eight chromosomes with 5S rDNA signal. Karyotype formula of Styphnolobium japonicum 2n = 2x = 14m + 12sm + 2st, cytotype 2B, arm ratio 2.6847, two chromosomes have 5S rDNA signal. Amorpha fruticose karyotype 2n = 2x = 38m + 2sm, cytotype 1B, arm ratio 3.2058, four chromosomes possessed 5S rDNA signal. Both ends of all species’ chromosomes have (AG₃T₃)₃ signals. The results of this study provide chromosome numbers and a physical map, contributing to the construction of the Oligo-FISH barcode and providing molecular cytogenetics data for Fabaceae.