Multiple cyclin-dependent kinase complexes and phosphatases control G sub(2)/M progression in alfalfa cells

• Published in: Plant molecular biology Vol. 43; no. 5-6; pp. 595 - 605
• Main Authors: Meszaros, T, Miskolczi, P, Ayaydin, F, Pettko-Szandtner, A, Peres, A, Magyar, Z, Horvath, G V, Bako, L, Feher, A, Dudits, D
• Format: Journal Article
• Language: English
• Published: 01.08.2000
• Subjects: cdc25 gene; Medicago sativa
• ISSN: 0167-4412

Reversible phosphorylation of proteins by kinases and phosphatases plays a key regulatory role in several eukaryotic cellular functions including the control of the division cycle. Increasing numbers of sequence and biochemical data show the involvement of cyclin-dependent kinases (CDKs) and cyclins in regulation of the cell cycle progression in higher plants. The complexity represented by different types of CDKs and cyclins in a single species such as alfalfa, indicates that multicomponent regulatory pathways control G sub(2)/M transition. A set of cdc2-related genes (cdc2Ms A, B, D and F) was expressed in G sub(2) and M cells. Phosphorylation assays also revealed that at least three kinase complexes (Cdc2Ms A/B, D and F) were successively active in G sub(2)/M cells after synchronization. Interaction between alfalfa mitotic cyclin (Medsa; CycB2; 1) and a kinase partner has been reported previously. The present yeast two-hybrid analyses showed differential interaction between defined D-type cyclins and Cdc2Ms kinases functioning in G sub(2)/M phases. Localization of Cdc2Ms F kinase to the preprophase band (PPB), the perinuclear ring in early prophase, the mitotic spindle and the phragmoplast indicated a pivotal role for this kinase in mitotic plant cells. So far limited research efforts have been devoted to the functions of phosphatases in the control of plant cell division. A homologue of dual phosphatase, cdc25, has not been cloned yet from alfalfa; however tyrosine phosphorylation was indicated in the case of Cdc2Ms A kinase and the p super(13sucl)-bound kinase activity was increased by treatment of this complex with recombinant Drosophila Cdc25. The potential role of serine/threonine phosphatases can be concluded from inhibitor studies based on okadaic acid or endothall. Endothall elevated the kinase activity of p13 super(sucl)-bound fractions in G sub(2)-phase alfalfa cells. These biochemical data are in accordance with observed cytological abnormalities. The present overview with selected original data outlines a conclusion that emphasizes the complexity of G sub(2)/M regulatory events in flowering plants.