A cytosolic vegetative storage protein (TrVSP) of white clover is encoded by a cold-inducible gene
Résumé
The stolons of white clover (Trifolium repens L.) contain a predominant 17.3-kDa protein, previously characterized as a vegetative storage protein (VSP), which accumulates under autumn and winter conditions. Its full-length complementary DNA, TrVsp, was obtained and its 157 amino acid sequence deduced. This VSP has common characteristics to stress-responsive proteins (high neutral amino acid content and potential alpha helices in its secondary structure) and shows high homologies to abscisic acid-responsive and pathogenesis-related-10 proteins. The lack of any common amino acid sequence domains with known dehydrins or late embryogenesis abundant proteins suggests that clover VSP is not related to these proteins. Antibodies raised against the protein were produced and used in light and electron microscopic studies to show that it is localized to the cytosol of cortical parenchyma cells. This is in agreement with the VSP sequence, which does not contain any transit peptide signal. The accumulation of the transcript and the protein in roots is quickly induced by root chilling, suggesting a direct transcriptional regulation of TrVsp in response to low temperatures. Altogether, these results suggest that the 17.3-kDa protein may have an additional or alternative function to its role in nitrogen storage and may confer putative tolerance to chilling in white clover.