Nematicidal Activity of Cyclotides: Toxicity Against Caenorhabditis elegans

Abstract

Cyclotides are a unique family of stable and cyclic mini-proteins found in plants that have nematicidal and anthelmintic activities. They are distributed across the Rubiaceae, Violaceae, Fabaceae, Cucurbitaceae, and Solanaceae plant families, where they are posited to act as protective agents against pests. In this study, we tested the nematicidal properties of extracts from four major cyclotide-producing plants, Oldenlandia affinis, Clitoria ternatea, Viola odorata, and Hybanthus enneaspermus, against the free-living model nematode Caenorhabditis elegans. We evaluated the nematicidal activity of the cyclotides kalata B1, cycloviolacin O2, and hyen D present in these extracts and found them to be active against the larvae of C. elegans. Both the plant extracts and isolated cyclotides exerted dose-dependent toxicity on the first-stage larvae of C. elegans. Isolated cyclotides caused death or damage upon interacting with the worms’ mouth, pharynx, and midgut or membrane. Cycloviolacin O2 and hyen D produced bubble-like structures around the C. elegans membrane, termed blebs, implicating membrane disruption causing toxicity and death. All tested cyclotides lost their toxicity when the hydrophobic patches present on them were disrupted via a single-point mutation. The present results provide a facile assay design to measure and explore the nematicidal activities of plant extracts and purified cyclotides on C. elegans.

Cyclotides: The next generation in biopesticide development for eco‐friendly agriculture

“…Cyclotides with a stable ring structure can easily penetrate pests' bodies and destroy them from the inside. 83,84,88 The interaction between cyclotides and pest cells is closely linked to the hydrophobic patch and bioactive site present on their structural surface. This connection plays a significant role in the disruption of cell membranes, leading to cell lysis.…”

“…This connection plays a significant role in the disruption of cell membranes, leading to cell lysis. 72,83,88,[97][98][99] The CCK motif serves to effectively stabilize the structure of the cyclotide, thereby preventing any potential structural rearrangement that may occur upon interaction with receptors. 100 Some studies have also shown that cyclotides are highly toxic in the early stages of the insect's life cycle, the juvenile phase contributing to great devastation on the flora when they need a lot of nutrients to mature.…”

“…67,84,101,102 For species whose cell membranes are not as complex and rigid to penetrate, such as bacteria, nematodes, and mollusks, cyclotides easily disturb the arrangement of lipids on the membrane, causing severe damage to cells. 71,88,[103][104][105] The mutual binding of cyclotides is dependent on specific hydrophobic patches and the positioning of polar residues on their surface, which is determined by their sequence structure. 99 The force for initial binding by electrostatic attraction is also reported.…”

Prospection of Nematotoxic Aqueous Seeds Extracts Derived from the Preserved Arachis (Fabaceae) Germplasm Bank

“…Brazil boasts one of the planet's richest biodiversities, making it a significant source of natural, plant-based products. A variety of plant species have yielded crude aqueous extracts (ACEs) that exhibit noteworthy nematicidal effectiveness against M. incognita egg hatchability and juvenile mortality [23][24][25] Notably, several species within the Fabaceae family, including those within the genus Arachis, have shown promise as potential sources of nematotoxic compounds [26,27].…”