Abstract
Cellulose synthesis, but not its degradation, is generally thought to be required for plant cell growth. In this work, we cloned a dinoflagellate cellulase gene, dCel1, whose activities increased significantly in G(2)/M phase, in agreement with the significant drop of cellulose content reported previously. Cellulase inhibitors not only caused a delay in cell cycle progression at both the G(1) and G(2)/M phases in the dinoflagellate Crypthecodinium cohnii, but also induced a higher level of dCel1p expression. Immunostaining results revealed that dCel1p was mainly localized at the cell wall. Accordingly, the possible role of cellulase activity in cell cycle progression was tested by treating synchronized cells with exogenous dCelp and purified antibody, in experiments analogous to overexpression and knockdown analyses, respectively. Cell cycle advancement was observed in cells treated with exogenous dCel1p, whereas the addition of purified antibody resulted in a cell cycle delay. Furthermore, delaying the G(2)/M phase independently with antimicrotubule inhibitors caused an abrupt and reversible drop in cellulase protein level. Our results provide a conceptual framework for the coordination of cell wall degradation and reconstruction with cell cycle progression in organisms with cell walls. Since cellulase activity has a direct bearing on the cell size, the coupling between cellulase expression and cell cycle progression can also be considered as a feedback mechanism that regulates cell size.
Highlights
Cellular growth, but not degradation of cellular constituents, is generally considered to be coupled to cell cycle progression, resulting in the homeostasis of cell size
To investigate if cellulase activities are required for cell cycle progression in C. cohnii, the cellulase inhibitors cellobiose (100 mM) and sodium hexachloropalladate (IV) tetrahydrate (SHPT) (50 mM) were added at T = 0 or at T = 7 to a synchronized population of cells
Is cell wall degradation required for and coordinated with cell cycle progression? there is some documentation about the regulation of cellulase expression levels in plants and fungi (Beguin and Aubert, 1994; Ilmen et al, 1997; Nicol et al, 1998; Park et al, 2003; Ohnishi et al, 2007), no data suggests a cell cycle–regulated cellulase level
Summary
But not degradation of cellular constituents, is generally considered to be coupled to cell cycle progression, resulting in the homeostasis of cell size. Cell walls are not static, and changes in their architecture, which are defined by synthesis, degradation, and reorganization of individual cell wall components, play a key role in the regulation of many physiological and developmental processes. Dissolution of cell wall polysaccharides during growth and morphogenesis requires concerted activities of different cell wall enzymes, such as cellulase (endo-b-1,4-glucanases) (Hoson, 1993; Cosgrove, 1999; Carpita and McCann, 2000) and expansins (Carpita and Gibeaut, 1993; McQueen-Mason and Cosgrove, 1995; Cosgrove, 1998) in plants and chitinase and. Endoglucanases play an important role in many plant developmental processes, including abscission (Tucker et al, 1988; Kemmerer and Tucker, 1994; del Campillo and Bennett, 1996), fruit ripening (Fischer and Bennett, 1991), and adventitious root initiation (Kemmerer and Tucker, 1994). The positive correlation between the expression of some plant endoglucanases (e.g., KOR in Arabiodopsis) and rapid cell elongation suggests a role for endoglucanases in cell expansion
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