Multiple cyclin-dependent kinase complexes and phosphatases control G2/M progression in alfalfa cells.
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 G2/M transition. A set of cdc2-related genes (cdc2Ms A, B, D and F) was expressed in G2 and M cells. Phosphorylation assays also revealed that at least three kinase complexes (Cdc2Ms A/B, D and F) were successively active in G2/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 G2/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(13suc1)-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 p(13suc1)-bound fractions in G2-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 G2/M regulatory events in flowering plants.
Mészáros
T
T
Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, Szeged.
Miskolczi
P
P
Ayaydin
F
F
Pettkó-Szandtner
A
A
Peres
A
A
Magyar
Z
Z
Horváth
G V
GV
Bakó
L
L
Fehér
A
A
Dudits
D
D
D016203:CDC2 Protein Kinase / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism; D016195:G2 Phase / Q000502:physiology*; D006657:Histones / Q000378:metabolism; D000455:Medicago sativa / Q000166:cytology* / Q000201:enzymology / Q000502:physiology; D008938:Mitosis / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D010937:Plant Growth Regulators / Q000378:metabolism / Q000502:physiology
D016213:Cyclins; D006657:Histones; D010937:Plant Growth Regulators; D016203:CDC2 Protein Kinase; D018844:Cyclin-Dependent Kinases; D010749:Phosphoprotein Phosphatases; D010744:Phosphoric Monoester Hydrolases