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Plants have evolved many strategies to protect themselves from attack, including peptide toxins that are ribosomally synthesized and thus adaptable directly by genetic polymorphisms. Certain toxins in Clitoria ternatea (butterfly pea) are cyclic cystine-knot peptides of c. 30 residues, called cyclotides, which have co-opted the plant's albumin-1 gene family for their production. How butterfly pea albumin-1 genes were commandeered and how these cyclotides are utilized in defence remain unclear. The role of cyclotides in host plant ecology and biotechnological applications requires exploration., We characterized the sequence diversity and expression dynamics of precursor and processing proteins implicated in butterfly pea cyclotide biosynthesis by expression profiling through RNA-sequencing ( RNA-seq). Peptide-enriched extracts from various organs were tested for activity against insect-like membranes and the model nematode Caenorhabditis elegans., We found that the evolution and deployment of cyclotides involved their diversification to exhibit different chemical properties and expression between organs facing different defensive challenges. Cyclotide-enriched fractions from soil-contacting organs were effective at killing nematodes, whereas similar enriched fractions from aerial organs contained cyclotides that exhibited stronger interactions with insect-like membrane lipids., Cyclotides are employed as versatile and combinatorial mediators of defence in C. ternatea and have specialized to affect different classes of attacking organisms. [ABSTRACT FROM AUTHOR]

ABSTRACT Mini-proteins (or peptides) with disulfide bond/s and a cyclic backbone offer exciting opportunities for applications in medicine, as these ribosomally synthesized and posttranslationally modified peptides are exceptionally stable and amenable to grafting epitopes with desirable activities. Here I discuss important aspects of the discovery and applications of disulfide-bonded cyclic peptides from seeds, i.e., the trypsin inhibitor cyclotides and the preproalbumin with sunflower trypsin inhibitor-derived peptides, focusing on bioanalytical methods for and insights generated from their discovery as well as their potential use as engineering scaffolds for peptide-based drug design. The recent discovery of their precursors and processing enzymes could potentially enable in planta production of designer disulfide-bonded cyclic peptides, preferably in edible seeds, and address the demand for new biopharmaceutical peptides in a cost-effective manner. © 2015 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 104: 804-814, 2015. [ABSTRACT FROM AUTHOR]