Abstract
Endoreduplication and resulting increase in the nuclear DNA content have major impacts on plant 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 endocycle, we have shown that the progression of plant endocycle requires the DNA topoisomerase VI (topo VI) protein complex. Mutants that lack functional topo VI display an ATM- and ATR-dependent DNA damage response only in endoreduplicating cells, suggesting that topo VI is specifically required during endocycle. Furthermore, our study of cell size in isogenic diploid and tetraploid plants provides strong genetic evidence that increasing ploidy is coupled with, and contributes directly to, an increase in cell size. Based on these results, I will discuss the molecular mechanisms of endoreduplication and cell-size control in plants.
