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Ubiquitin conjugation to endogenous proteins in the dormant tuber of Helianthus tuberosus and during the first cell cycle
Author(s) -
Scoccianti Valeria,
Corsi Dario,
Magnani Mauro
Publication year - 1997
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1997.tb01822.x
Subject(s) - ubiquitin , ubiquitin conjugating enzyme , ubiquitin ligase , proteolysis , f box protein , biochemistry , biology , cell cycle , protein degradation , microbiology and biotechnology , cell division control protein 4 , enzyme , cell , gene
Ubiquitin is a small protein involved in an ATP‐dependent proteolytic pathway in all eukaryotes. This pathway has been demonstrated to be required for both the bulk degradation of cellular proteins and the targeted proteolysis of specific regulatory proteins. We have investigated the presence of ubiquitin (Ub) and the ubiquitin‐conjugating system in dormant and activated tubers of Helianthus tuberosus L. cv. OB 1 that represent a widely used model system for studies on the cell cycle in plants. Immunoblot experiments revealed the presence of free ubiquitin and ubiquitin conjugates. Furthermore, the presence of an active ubiquitin‐conjugating system, both time‐ and ATP‐dependent, was demonstrated by incubation with 125 I‐labeled ubiquitin. A few proteins able to form thiol esters with 125 I‐Ub and probably corresponding to ubiquitin‐conjugating enzymes, E1 and E2s, were also found. During the first cell cycle, several proteins become ubiquitinated. In particular a large amount of protein conjugates was present at 6 h when the lowest content of free ubiquitin was found. Subsequently, a dramatic decrease in ubiquitin conjugates occurred. It is well known that cell cycle progression in eukaryotes depends on cyclin levels and cyclin B degradation is ubiquitin‐ and ATP‐dependent. By immunoblot experiments we showed that cyclin B in H. tuberosus is present as at least two protein bands of 50 and 54 kDa and that their amounts undergo profound changes during the cell cycle. The 54‐kDa band was also recognized by an anti‐ubiquitin antibody. These data seem to indicate that in H. tuberosus activated tuber slices, the ATP‐dependent ubiquitin proteolytic pathway is involved in the dedifferentiation process occurring after the artificial break of dormancy when the cells acquire the characteristics linked to the meristematic state.