Ubiquitin conjugation to endogenous proteins in the dormant tuber of Helianthus tuberosus and during the first cell cycle

Abstract

M. 1997. Ubiquitin conjugation to endogenous proteins in the dormant tuber of Helianthus tuberosus and during the first cell cycle. -Physiol. Plant. 101:77-85.Ubiquitin is a small protein involved in an ATP-dependent proteoiytic 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 ''^I-labeled ubiquitin. A few proteins able to form thiol esters with '~^I-Ub and probably corresponding to ubiquitin-conjugating enzymes. El 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.

Inhibition of Proteasome Activity Strongly Affects Kiwifruit Pollen Germination. Involvement of the Ubiquitin/Proteasome Pathway as a Major Regulator

“…In plants, the ubiquitin-mediated proteolytic pathway is implicated in a variety of cellular processes, including alkaloid synthesis (Fernandez and DeLuca, 1994), senescence and stress responses (Belknap and Garbarino, 1996;Stephenson and Rubinstein, 1998), hypersensitive and defense responses (Becker et al, 1993(Becker et al, , 2000, vascular tissue differentiation (Woffenden et al, 1998), seed formation (Ferreira et al, 1995), and cell cycle regulation (Scoccianti et al, 1997;Genschik et al, 1998).…”

Immunocytochemical localization of ubiquitin and proteasomes in spermatids during spermiogenesis ofChara vulgaris(Charophyceae)

“…The ubiquitin/26S proteasome pathway controls many important regulatory processes. In plants, the ubiquitin-mediated proteolytic pathway is implicated in senescence and stress responses (Belknap & Garbarino, 1996;Stephenson & Rubinstein, 1998), hypersensitive and defence responses (Becker et al, 1993;2000), vascular tissue differentiation (Woffenden et al, 1998), cell cycle regulation (Scoccianti et al, 1997;Genschik et al, 1998), seed formation (Ferreira et al, 1995), pollen germination (Sperenza et al, 2001) and organogenesis Yanagawa et al, 2002).…”

Development‐related changes of protein ubiquitination in pollen from male and female kiwifruit (Actinidia deliciosa)

“…In plants, the pattern of ubiquitinated proteins changes during floral development (Courtney et al 1994), zygotic embryogenesis (Almoguera et al 1995), aging and greening of leaves (Veierskov et al 1992), seed formation (Ferreira et al 1995), and cell cycle progression (Scoccianti et al 1997). Callis and Bedinger (1994) observed that a developmentally‐related loss of free ubiquitin and ubiquitinated proteins occurs during pollen maturation in maize inbred line Ky21.…”