Gastredner: Dr. Keiko Sugimoto

RIKEN Yokohama Institute, Plant Science Center, Japan

How cells determine their final size and what controls this process are fundamental questions in biology. Endoreduplication and resulting increase in the nuclear DNA content have major impacts on plant cell growth but the molecular mechanisms that underlie this process remain largely unknown. Through the characterization of Arabidopsis mutants, hypocotyl6-7, root hairless1-3, and brassinosteroid insensitive 3-5, that have defects in the endocycle, we have shown that the progression of the plant endocycle requires the DNA topoisomerase VI (topo VI) protein complex. This was an important finding to show that the endocycle is not just a shortcut of the mitotic cell cycle, as generally believed, and that at least some process within the endocycle requires proteins unique to it. In addition, we found that loss of the plant topo VI components triggers an ATM- and ATR-dependent DNA damage response in endoreduplicating cells, and this response coincides with the up-regulation of a core cell cycle gene, cyclin B1;1, in the same cell types, suggesting a novel functional link between the DNA damage response and cell cycle control. Based on these results, I will discuss the molecular mechanisms of endoreduplication and cell-size control in plants.

Gastgeber: Dr. Christian Fleck

E-Mail: Christian.Fleck@fdm.uni-freiburg.de