Bio-detoxification of ricin in castor bean (Ricinus communis L.) seeds

Natália L Sousa,Pabline M Vieira,Glaucia B Cabral,Aisy B Baldoni,Francisco J L Aragão

doi:10.1038/s41598-017-15636-7

Abstract

Ricin is a highly toxic ribosome-inactivating lectin occurring in the seeds of castor bean (Ricinus communis L.). Castor bean grows throughout tropical and sub-tropical regions and is a very important crop due to its high seed content of ricinoleic acid, an unusual fatty acid, which has several industrial applications. However, due to the presence of the toxin, castor bean can cause death after the exposure of animals to low doses of ricin through skin contact, injection, inhalation or oral routes. Aiming to generate a detoxified genotype, we explored the RNAi concept in order to silence the ricin coding genes in the endosperm of castor bean seeds. Results indicated that ricin genes were effectively silenced in genetically modified (GM) plants, and ricin proteins were not detected by ELISA. Hemagglutination activity was not observed with proteins isolated from GM seeds. In addition, we demonstrated that seed proteins from GM plants were not toxic to rat intestine epithelial cells or to Swiss Webster mice. After oil extraction, bio-detoxified castor bean cake, which is very rich in valuable proteins, can be used for animal feeding. Gene silencing would make castor bean cultivation safer for farmers, industrial workers and society.

Highlights

Castor bean (Ricinus communis L.) is commercially cultivated due to the high quality and content of its seed oil
We explored the RNA interference (RNAi) concept to silence the ricin gene in castor bean seeds in order to generate a non-toxic castor bean genotype
An intron-hairpin vector was designed, in which a 460 bp fragment of the A-chain ricin gene was directionally cloned in sense and antisense (Δricin cassette) to generate dsRNA during transcription (Fig. 1a)

Summary

Results and Discussion

An intron-hairpin vector was designed, in which a 460 bp fragment of the A-chain ricin gene was directionally cloned in sense and antisense (Δricin cassette) to generate dsRNA during transcription (Fig. 1a). MRNAs of several sizes were observed in non-transgenic seeds, probably due to the fact that 19 members of ricin/ RCA120 genes and pseudogenes containing the A-chain sequence were found in the castor bean genome. These fragments could vary from 0.8 to 1.7 kb[21]. There were no statistical differences between the viability values of 97% and 78% These results were corroborated by the fact that protein synthesis was 40% and 90% inhibited by cells cultivated for 5 h with proteins from non-transgenic seeds containing 0.1 and 1 ng ricin/mL, respectively (Fig. 4b). This biotechnology will have a major impact on the cultivation of castor bean, a plant already adapted to suboptimal environments, with a consequent positive effect on manufacturing ricinoleic acid-based goods and livestock production

Methods

Author Contributions

Additional Information