Human salivary proline-rich proteins are known to bind efficiently to tannins as a mechanism of detoxifications in mammals. However, no such response on protein level has been described for invertebrates [1]. Recent results from a microarray experiment indicated a remarkable concentration dependent increase in the expression of the hitherto uncharacterized gene T22D1.2 in Caenorhabditis elegans after treatment with oligomeric procyanidins (OPC) [2].
BLASTp analysis of the predicted protein sequence revealed a high similarity to the human Basic salivary proline-rich protein 2 (PRB2). For unambigious localization of the specific sites of gene expression and excretion of this protein, the promoter was fused to GFP either directly or with the sequence of the signal peptide inserted. In worms containing the GFP construct including the signal peptide following the promoter sequence, fluorescence immediately disappeared. However, a strong concentration dependent increase in fluorescence was observed in the worms’ intestine after treatment for 6 h with an OPC enriched hydroethanolic (1:1) leaf extract (0.2 – 2 mg/mL) from Combretum mucronatum in C. elegans containing the promoter-GFP fusion. The negative control did not show any signs of fluorescence. These findings were additionally confirmed by qPCR experiments.
Due to its structural similarity to PRB2, its lack of constitutive expression and the strong up-regulation upon treatment with OPCs, this gene could likely be involved in the defense mechanism of C. elegans against tannins.
References
[1] Barbehenn RV, Constabel CP. Tannins in plant–herbivore interactions. Phytochemistry 2011; 72: 1551-1565.
[2] Spiegler V, Sendker J, Petereit F, Liebau E, Hensel A. Bioassay-Guided Fractionation of a Leaf Extract from Combretum mucronatum with Anthelmintic Activity: Oligomeric Procyanidins as the Active Principle. Molecules 2015; 20: 14810-14832.