Abstract
Endoreduplication is a special cell cycle that increases ploidy without cell and nuclear division. In plants endoreduplication is essential for development. To understand this mechanism, we isolated mutants that showed increased polyploidy phenotypes in dark-grown hypocotyls by screening of RIKEN Arabidopsis activation tagging lines. A dominant mutant, ipd1-D (increased polyploidy level in darkness 1-D), shows longer hypocotyls and increased polyploidy levels in dark-grown seedlings. However, this mutant didn't show any significant phenotype compared with wild type in light-grown seedlings. The corresponding gene encodes a protein that contains a mono-ubiquitin-binding CUE domain variant that is specific to plants. IPD1 is specifically expressed at regions where rapid cell elongation is observed. Furthermore we show that blue and far-red light can suppress the ploidy increase in ipd1-D. These results suggest that IPD1 is a positive regulator of the endocycle and controls cell elongation leading to hypocotyl elongation.
