Abstract
Differential auxin distribution has been proposed to act as a morphogen to set up distinct zones for cell division, cell expansion, and cell differentiation. It is well known that cell differentiation is usually associated with transition from the mitotic cell cycle to the endocycle. This switch is assumed to be controlled by spatiotemporal regulation of cyclin-dependent kinase (CDK) activities, but its regulatory mechanisms remain unknown.
Plants have six types of CDK, among which CDKA and CDKB play a key role in cell cycle progression. We have recently found that a reduction in the CDKB2 level was well correlated with endocycle induction in response to genotoxic stress. Therefore, we assumed that quantitative regulation of CDKB2 may be also important in transition to the endocycle during plant development. When the CDKB2 reporter lines of Arabidopsis were treated with auxin antagonist, the CDKB2 level was downregulated by proteolysis earlier than by a reduction in the transcript level. Our recent report suggested that CDKB2 may be also controlled by protein stabilization, thus we are testing how the CDKB2 level is balanced in root tips to maintain the continuous root growth.
