The Tr-cp 14 cysteine protease in white clover (Trifolium repens) is localized to the endoplasmic reticulum and is associated with programmed cell death during development of tracheary elements
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Cysteine proteases are known to be associated with programmed cell death, developmental senescence and some types of pathogen and stress-induced responses. In the present study, we have characterized the cysteine protease Tr-cp 14 in white clover (Trifolium repens). Tr-cp 14 belongs to the C1A family of cysteine proteases with homology to XCP1 and XCP2 from Arabidopsis thaliana and p48h-17 from Zinnia elegans, which previously have been reported to be associated with tracheary element differentiation. The proform as well as the processed form of the protein was detected in petioles, flowers and leaves, but the processed form was more abundant in leaves and petioles than in flowers. The Tr-cp 14 protein was localized to differentiating tracheary elements within the xylem, indicating that the cysteine protease is involved in protein re-mobilization during tracheary element differentiation. Immunogold studies suggest that the protease prior to the burst of the vacuole was associated to the ER cisternae. After disruption of the tonoplast, it was found in the cytoplasm, and, in later stages, associated with disintegrating material dispersed throughout the cell.
KeywordsCysteine protease Endoplasmic reticulum Immunolocalization Tracheary element differentiation Trifolium repens
Sanne Seval and Ole Braad Hansen, Aarhus University, are acknowledged for technical and horticultural assistance, respectively. Anke Schäfer, University of Kiel, is acknowledged for purification of the antibody. Marita Beese is acknowledged for assistance in the electron microscopical preparations. The project was supported by the Danish Food Industry Agency through the programme “Biotechnology in Food Research”.
Conflict of interest
The authors declare that they have no conflict of interest.