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Calendar Name: seminars
Scheduled for: Tuesday, July 2 2013, 14:00 - 15:30
Event text:    Prof Masaaki Umeda & Dr Naoki Takahashi
	       
	       Nara Institute of Science and Technology 
	       
	       Ikoma 
	       Nara 
	       JAPAN
Details:       “Cell-cycle control in Arabidopsis roots by internal and
	       external factors”
	       
	       ABSTRACT
	       Plant roots respond to various internal and external
	       signals and adjust themselves to changes of
	       environmental conditions. Previous studies indicate that
	       an antagonistic interaction between auxin and cytokinin
	       hormones determines meristem size. We found that, in
	       Arabidopsis, cytokinins promote the transition from the
	       mitotic cell cycle to the endocycle, a modified cell
	       cycle in which DNA replication is repeated without
	       mitosis and cytokinesis. The cytokinin-activated type-B
	       response regulator up-regulates the expression of
	       CCS52A1, which encodes an activator of an E3 ubiquitin
	       ligase, anaphase-promoting complex/cyclosome (APC/C),
	       thereby promoting the onset of the endocycle and
	       restricting meristem size. Our results indicate that
	       cytokinins directly control the cell cycle and maintain
	       root meristem size. Under stressful conditions, however,
	       down-regulation of mitotic activity in the meristem
	       plays an important role to sustain the suppressive state
	       of root growth. Recently we found that repressor-type
	       MYB transcription factors are essential to suppress
	       mitotic activity in DNA-damaged cells, causing cell
	       death in the stem cell region and promoting endocycle
	       onset in the root meristem. We shall discuss how
	       different types of MYB transcription factors control
	       mitotic activity, and how cyclin-dependent kinase
	       activities are involved in the regulation under changing
	       environmental conditions.

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