The perennial leguminous herb Clitoria ternatea (butterfly pea) has attracted significant interest based on its agricultural and medical applications, which range from use as a fodder and nitrogen fixing crop, to applications in food coloring and cosmetics, traditional medicine and as a source of an eco-friendly insecticide. In this article we provide a broad multidisciplinary review that includes descriptions of the physical appearance, distribution, taxonomy, habitat, growth and propagation, phytochemical composition and applications of this plant. Notable amongst its repertoire of chemical components are anthocyanins which give C. ternatea flowers their characteristic blue color, and cyclotides, ultra-stable macrocyclic peptides that are present in all tissues of this plant. The latter are potent insecticidal molecules and are implicated as the bioactive agents in a plant extract used commercially as an insecticide. We include a description of the genetic origin of these peptides, which interestingly involve the co-option of an ancestral albumin gene to produce the cyclotide precursor protein. The biosynthesis step in which the cyclic peptide backbone is formed involves an asparaginyl endopeptidase, of which in C. ternatea is known as butelase-1. This enzyme is highly efficient in peptide ligation and has been the focus of many recent studies on peptide ligation and cyclization for biotechnological applications. The article concludes with some suggestions for future studies on this plant, including the need to explore possible synergies between the various peptidic and non-peptidic phytochemicals.
The evolution of plants is characterized by several rounds of ancient whole genome duplication, sometimes closely associated with the origin of large groups of species. A good example is the γ triplication at the origin of core eudicots. Core eudicots comprise about 75% of flowering plants and are characterized by the canalization of reproductive development. To better understand the impact of this genomic event, we studied the protein interaction network of MADS-domain transcription factors, which are key regulators of reproductive development. We accurately inferred, resurrected and tested the interactions of ancestral proteins before and after the triplication and directly compared these ancestral networks to the networks of Arabidopsis and tomato. We find that the γ triplication generated a dramatically innovated network that strongly rewired through the addition of many new interactions. Many of these interactions were established between paralogous proteins and a new interaction partner, establishing new redundancy. Simulations show that both node and edge addition through the triplication were important to maintain modularity in the network. In addition to generating insights into the impact of whole genome duplication and elementary processes involved in network evolution, our data provide a resource for comparative developmental biology in flowering plants.
Clitoria ternatea (butterfly pea) is currently the only species in the Fabaceae plant family that is known to produce a suite of small circular peptides called cyclotides that are implicated in plant defence. C. ternatea has been shown to produce upwards of 70 cyclotides. With their ultrastable structures, cyclotides have attracted significant interest for use as scaffolds for the production of peptide-based pharmaceuticals. Similarly, their native insecticidal activity has attracted interest for use in agriculture, resulting in the commercial release of an eco-friendly bio-insecticide (Sero-X ® ) derived from C. ternatea extracts. With the biotechnological potential of C. ternatea evident, this thesis aims to characterise the key gene regulatory factors that guide cyclotide peptide expression levels, diversity, and bioactivity.Chapter 1 of this thesis provides background literature on cyclotides, their biological properties and the potential factors that can regulate their expression. Chapter 2 describes the diversity of cyclotides uncovered in extracts from C. ternatea accessions sourced worldwide. Notable variations in the cyclotide peptide profiles were observed. For instance, some accessions do not produce detectable Cter M, typically observed as the most highly expressed cyclotide in C. ternatea.Genomic and cDNA sequencing of these unique accessions revealed that the CterM precursor genes exhibited missense mutations, presumably leading to the lack of observed Cter M peptide expression.Other cyclotides also varied significantly in relative abundance between accessions which translated to differences in insecticidal properties, with extracts from C. ternatea accessions with the highest cyclotide content being the most potent. Despite the diversity of cyclotides uncovered, the overall genetic diversity of C. ternatea accessions was found to be very similar, as measured using randomly amplified polymorphic DNA marker analysis. This suggests that cyclotides are probably diversifying faster than the background diversification rate.Factors that contribute to the diversity of cyclotide expression were subsequently elucidated in Chapter 3. Using a combination of genome walking and nanopore sequencing, the promoter regions of six cyclotides (CterM, cliotideT1, Cter6, Cter14, Cter16, and cliotideT9) were sequenced and the cis-regulatory elements (CREs) were characterised. Across the six promoters, there was substantial variation in the CREs composition. However, the most abundant CREs identified were shown to associate with seed development and storage, vegetative tissue-related expression, and abiotic and biotic stress response, suggesting these are key regulatory roles for cyclotides in C. ternatea. Further experiments provided evidence for the role of cyclotides in plant defence, with significant upregulation of C. ternatea cyclotide expression detected upon exogenous application of the three defence hormones in plants: jasmonate, ethylene and salicylic acid.iii The differences in cyclotide peptide expression leve...
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