Abstract
Plant cells frequently undergo endoreduplication, a process in which chromosomal DNA is successively duplicated in the absence of mitosis. However, the regulatory mechanisms for its termination remain unclear although plants tightly control the ploidy level in each cell type. In the process of searching for regulatory factors of endoreduplication, the promoter of an Arabidopsis A2 type cyclin gene, CYCA2;3, was revealed to be active in developing trichomes during the termination period of endoreduplication. Loss-of-function mutations of CYCA2;3 semi-dominantly promoted endocycles and increased ploidy levels in various organs, but did not significantly affect the proportion of cells destined to undergo endoreduplication. Consistent with this result, expression of the CYCA2;3-GFP restrained endocycles in a dose-dependent manner. Moreover, a mutation in the destruction box of CYCA2;3 stabilized the fusion protein and enhanced the restraint. We conclude that CYCA2;3 negatively regulates endocycles and acts as a key regulator of ploidy levels in Arabidopsis endoreduplication.
