Induction of proline-rich proteins in response to tannin treatment in Caenorhabditis elegans.

Salivary proline-rich proteins (PRPs) represent a common mechanism of defense against tannins in mammals. Few reports exist regarding the occurrence or PRPs with similar function in nematodes and none of these proteins or their coding genes have been functionally characterized so far. In Caenorhabditis elegans, two genes (clx-1 and T22D1.2) were strongly induced upon tannin treatment of the nematodes, both of them potentially encoding proline-rich proteins. Therefore, translation of these genes into proteins was confirmed and the expression pattern was investigated in more detail. Particularly T22D1.2 was found to be exclusively up-regulated in worms treated with test substances possessing astringent properties, especially tannins, whereas no expression was observed for any other stressor or in the untreated control group. Similar to mammalian PRPs, repetitive proline-rich sequences were identified in both of the corresponding proteins. A potential role in tannin defense was supported by an increased survival of tannin-treated worms when T22D1.2 was constitutively expressed under the vit-5 promoter. However, no differences were observed in the clx-1 and T22D1.2 knockout mutants in comparison to the wild type, respectively. Within the current study, evidence was provided for the existence of repetitive proline-rich proteins in the free-living nematode C. elegans, of which particularly T22D1.2 may be involved in tannin defense.