Transcriptomic profiling of the medicinal plant Clitoria ternatea: identification of potential genes in cyclotide biosynthesis.

Clitoria ternatea a perennial climber of the Fabaceae family, is well known for its agricultural and medical applications. It is also currently the only known member of the Fabaceae family that produces abundant amounts of the ultra-stable macrocyclic peptides, cyclotides, across all tissues. Cyclotides are a class of gene-encoded, disulphide-rich, macrocyclic peptides (26-37 residues) acting as defensive metabolites in several plant species. Previous transcriptomic studies have demonstrated the genetic origin of cyclotides from the Fabaceae plant family to be embedded in the albumin-1 genes, unlike its counterparts in other plant families. However, the complete mechanism of its biosynthesis and the repertoire of enzymes involved in cyclotide folding and processing remains to be understood. In this study, using RNA-Seq data and de novo transcriptome assembly of Clitoria ternatea, we have identified 71 precursor genes of cyclotides. Out of 71 unique cyclotide precursor genes obtained, 51 sequences display unique cyclotide domains, of which 26 are novel cyclotide sequences, arising from four individual tissues. MALDI-TOF mass spectrometry analysis of fractions from different tissue extracts, coupled with precursor protein sequences obtained from transcriptomic data, established the cyclotide diversity in this plant species. Special focus in this study has also been on identifying possible enzymes responsible for proper folding and processing of cyclotides in the cell. Transcriptomic mining for oxidative folding enzymes such as protein-disulphide isomerases (PDI), ER oxidoreductin-1 (ERO1) and peptidylprolyl cis-trans isomerases (PPIases)/cyclophilins, and their levels of expression are also reported. In particular, it was observed that the CtPDI genes formed plant-specific clusters among PDI genes as compared to those from other plant species. Collectively, this work provides insights into the biogenesis of the medicinally important cyclotides and establishes the expression of certain key enzymes participating in peptide biosynthesis. Also, several novel cyclotide sequences are reported and precursor sequences are analysed in detail. In the absence of a published reference genome, a comprehensive transcriptomics approach was adopted to provide an overview of diverse properties and constituents of C. ternatea.

Immunostimulating and Gram-negative-specific antibacterial cyclotides from the butterfly pea (Clitoria ternatea).

UNLABELLED: Cyclotides are plant-derived, cyclic miniproteins with three interlocking disulfide bonds that have attracted great interests because of their excellent stability and potential as peptide therapeutics. In this study, we characterize the cyclotides of the medicinal plant Clitoria ternatea (butterfly pea) and investigate their biological activities. Using a combined proteomic and transcriptomic method, we identified 41 novel cyclotide sequences, which we named cliotides, making C. ternatea one of the richest cyclotide-producing plants to date. Selected members of the cationic cliotides display potent antibacterial activity specifically against Gram-negative bacteria with minimal inhibitory concentrations as low as 0.5 µm. Remarkably, they also possess prominent immunostimulating activity. At a concentration of 1 µm, cationic cliotides are capable of augmenting the secretion of various cytokines and chemokines in human monocytes at both resting and lipopolysaccharide-stimulated states. Chemokines such as macrophage inflammatory proteins 1α and 1ß, interferon γ-induced protein 10, interleukin 8 and tumor necrosis factor α were among the most upregulated with up to 129-fold increase in secretion level. These findings suggest cyclotides can serve as potential candidates for novel immunomodulating therapeutics. DATABASE: The protein sequences reported in this paper (cT13-cT21) are available in the UniProt Knowledgebase under the accession numbers C0HJS0, C0HJS1, C0HJS2, C0HJS3, C0HJS4, C0HJS5, C0HJS6, C0HJS7 and C0HJS8, respectively. The transcriptome data in this paper are available at the Sequence Read Archive database (NCBI) under accession number SRR1613316. The protein precursors reported in this paper (ctc13, ctc15, ctc17-ctc19, ctc21-ctc53) are available at GenBank under the accession numbers KT732712, KT732713, KT732714, KT732715, KT732716, KT732717, KT732718, KT732719, KT732720, KT732721, KT732722, KT732723, KT732724, KT732725, KT732726, KT732727, KT732728, KT732729, KT732730, KT732731, KT732732, KT732733, KT732734, KT732735, KT732736, KT732737, KT732738, KT732739, KT732740, KT732741, KT732742, KT732743, KT732744, KT732745, KT732746, KT732747, KT732748 and KT732749, respectively.

Cloning and characterization of resistance gene analogs from under-exploited plant species

Genomic DNA sequences sharing homology with NBS region of resistance gene analogs were isolated and characterized from Pongamia glabra, Adenanthera pavonina, Clitoria ternatea and Solanum trilobatum using PCR based approach with primers designed from conserved regions of NBS domain. The presence of consensus motifs viz., kinase 1a, kinase 2, kinase 3a and hydrophobic domain provided evidence that the cloned sequences may belong to the NBS-LRR gene family. Conservation of tryptophan as the last residue of kinase-2 motif further confirms their position in non-TIR NBS-LRR family of resistance genes. The Resistance Gene Analogs (RGAs) cloned from P. glabra, A. pavonina, C. ternatea and S. trilobatum clustered together with well- characterized non-TIR-NBS-LRR genes leaving the TIR-NBS-LRR genes as a separate cluster in the average distance tree constructed based on BLOSUM62. All the four RGAs had high level of identity with NBS-LRR family of RGAs deposited in the GenBank. The extent of identity between the sequences at NBS region varied from 29 percent (P. glabra and S. trilobatum) to 78 percent (A. pavonina and C. ternatea), which indicates the diversity among the RGAs.