The life cycle of cyclotides: biosynthesis and turnover in plant cells

• Published in: Plant cell reports Vol. 39; no. 10; pp. 1359 - 1367
• Main Authors: Slazak, Blazej, Haugmo, Tobias, Badyra, Bogna, Göransson, Ulf
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-10-2020; Springer Nature B.V
• Subjects: Amino Acid Sequence; Biodegradation; Biomedical and Life Sciences; Biosynthesis; Biotechnology; Cell Biology; Cell culture; Chromatography, Liquid; Cyclic peptides; Cyclotides - biosynthesis; Cyclotides - chemistry; Cystine; Degradation; Endosperm; Endosperm - metabolism; Environmental factors; Life cycles; Life Sciences; Mass Spectrometry; N-15 labelling; Nitrogen Isotopes; Original; Original Article; Peptides; Plant Biochemistry; Plant cell suspension culture; Plant cells; Plant Cells - metabolism; Plant Sciences; Polypeptides; Proteolysis; Salts; Seedlings; Seedlings - metabolism; Seeds; Storage proteins; Viola; Viola - metabolism; Plant cell suspension culture; Cyclic peptides; Mass spectrometry; N labelling; Viola; 15N labelling
• DOI: 10.1007/s00299-020-02569-1
• EISSN: 1432-203X
• ISSN: 0721-7714; 1432-203X

Key message
Turnover rates have implications for understanding cyclotide biology and improving plant cell culture-based production systems.
Cyclotides are a family of polypeptides recognized for a broad spectrum of bioactivities. The cyclic, cystine knot structural motif imparts these peptides with resistance to temperature, chemicals and proteolysis. Cyclotides are found widely distributed across the Violaceae and in five other plant families, where their presumed biological role is host defense. Violets produce mixtures of different cyclotides that vary depending on the organ, tissue or influence of environmental factors. In the present study, we investigated the biosynthesis and turnover of cyclotides in plant cells.
Viola uliginosa
suspension cultures were grown in media where all nitrogen containing salts were replaced with their
15
N counterparts. This approach combined with LC–MS analysis allowed to separately observe the production of
15
N-labelled peptides and decomposition of
14
N cyclotides present in the cells when switching the media. Additionally, we investigated changes in cyclotide content in
V. odorata
germinating seeds. In the suspension cultures, the degradation rates varied for individual cyclotides and the highest was noted for cyO13. Rapid increase in production of
15
N peptides was observed until day 19 and subsequently, a plateau of production, indicating an equilibrium between biosynthesis and turnover. The developing seedling appeared to consume cyclotides present in the seed endosperm. We show that degradation processes shape the cyclotide pattern present in different tissues and environments. The results indicate that individual cyclotides play different roles—some in defense and others as storage proteins. The turnover of cyclotides should be accounted to improve cell culture production systems.