Antifungal activity of the ribosome‐inactivating protein BE27 from sugar beet (Beta vulgaris L.) against the green mould Penicillium digitatum

• Published in: Molecular plant pathology Vol. 17; no. 2; pp. 261 - 271
• Main Authors: Citores, Lucía, Iglesias, Rosario, Gay, Carolina, Ferreras, José Miguel
• Format: Journal Article
• Language: English
• Published: England Blackwell Science in collaboration with the British Society of Plant Pathology 01-02-2016; Blackwell Publishing Ltd; John Wiley & Sons, Inc; John Wiley and Sons Inc
• Subjects: Amino Acid Motifs; Amino Acid Sequence; Antifungal Agents - pharmacology; apoplast; Beta vulgaris - drug effects; Beta vulgaris - metabolism; Beta vulgaris - microbiology; Computer Simulation; defensin; green mould; Models, Molecular; Molecular Sequence Data; Original; Penicillium - drug effects; Penicillium - growth & development; Penicillium - physiology; Penicillium digitatum; plant defence; Plant Proteins - chemistry; Plant Proteins - metabolism; pokeweed antiviral protein (PAP); polynucleotide:adenosine glycosylase; Proteins; Ribosome Inactivating Proteins - chemistry; Ribosome Inactivating Proteins - metabolism; Ribosomes - metabolism; rRNA N-glycosylase; Sugar industry; plant defence; rRNA N-glycosylase; apoplast; green mould; polynucleotide:adenosine glycosylase; defensin; pokeweed antiviral protein (PAP)
• ISSN: 1464-6722; 1364-3703
• DOI: 10.1111/mpp.12278

The ribosome‐inactivating protein BE27 from sugar beet (Beta vulgaris L.) leaves is an apoplastic protein induced by signalling compounds, such as hydrogen peroxide and salicylic acid, which has been reported to be involved in defence against viruses. Here, we report that, at a concentration much lower than that present in the apoplast, BE27 displays antifungal activity against the green mould Penicillium digitatum, a necrotrophic fungus that colonizes wounds and grows in the inter‐ and intracellular spaces of the tissues of several edible plants. BE27 is able to enter into the cytosol and kill fungal cells, thus arresting the growth of the fungus. The mechanism of action seems to involve ribosomal RNA (rRNA) N‐glycosylase activity on the sarcin–ricin loop of the major rRNA which inactivates irreversibly the fungal ribosomes, thus inhibiting protein synthesis. We compared the C‐terminus of the BE27 structure with antifungal plant defensins and hypothesize that a structural motif composed of an α‐helix and a β‐hairpin, similar to the γ‐core motif of defensins, might contribute to the specific interaction with the fungal plasma membranes, allowing the protein to enter into the cell.