Cytokinin controls the cell cycle at mitosis by stimulating the tyrosine dephosphorylation and activation of p34cdc2-like H1 histone kinase

Abstract

In excised pith parenchyma from Nicotiana tabacum L. cv. Wisconsin Havana 38, auxin (naphthalene-1-acetic acid) together with cytokinin (6-benzylaminopurine) induced a greater than 40-fold increase in a p34cdc2-like protein, recoverable in the p13suc1-binding fraction, that had high H1 histone kinase activity, but enzyme induced without cytokinin was inactive. In suspension-cultured N. plumbaginifolia Viv., cytokinin (kinetin) was stringently required only in late G2 phase of the cell division cycle (cdc) and cells lacking kinetin arrested in G2 phase with inactive p34cdc2-like H1 histone kinase. Control of the Cdc2 kinase by inhibitory tyrosine phosphorylation was indicated by high phosphotyrosine in the inactive enzyme of arrested pith and suspension cells. Yeast cdc25 phosphatase, which is specific for removal of phosphate from tyrosine at the active site of p34cdc2 enzyme, was expressed in bacteria and caused extensive in-vitro activation of p13suc1-purified enzyme from pith and suspension cells cultured without cytokinin. Cytokinin stimulated the removal of phosphate, activation of the enzyme and rapid synchronous entry into mitosis. Therefore, plants can control cell division by tyrosine phosphorylation of Cdc2 but differ from somatic animal cells in coupling this mitotic control to hormonal signals.

In planta functions of the Arabidopsis cytokinin receptor family

“…Cytokinins were first discovered for their role in promoting cell division (1) and have since been implicated in stimulating both the G 1 3S phase transition (32) as well as the G 2 3M phase transition of the cell cycle (33). The reduced meristem activity seen in the triple mutant roots seems to be a consequence of a delay in the G 2 3M phase, as demonstrated by FACS experiments.…”

Differential Effect of Jasmonic Acid and Abscisic Acid on Cell Cycle Progression in Tobacco BY-2 Cells

“…The Tyr phosphatase activity of the enzyme specific for the CDK is positively regulated by cytokinins (Zhang et al, 1996). In human cells, cdc25 is also involved in the response to UV-mediated DNA damage in a p53-independent pathway, where DNA damage induces S-phase arrest via activation of Chk1 kinase, which phosphorylates cdc25A and targets it for proteasome degradation (Mailand et al, 2000).…”

“…Taken together, these data suggest that the induction of cell division by cytokinins involves increased expression of cycD3. However, the activity of phosphatase cdc25, which activates cyclindependent kinase (CDK) by the removal of a phosphate group from a Tyr moiety in the ATP-binding loop, has also been shown to be cytokinin dependent (Zhang et al, 1996). Redig et al (1996) demonstrated that the zeatin level fluctuates in synchronized tobacco BY-2 cells, peaking at late S and before G2/M transition.…”

Why Do Plant Cells Divide?

“…Functional homologs of weel+ have been identified in vertebrates, but they have yet to be found in plants. Evidence has been presented for mitotic control by reversible tyrosine phosphorylation of CDKs in cultured plant cells (Zhang et al, 1996).…”