The A-type cyclin CYCA2;3 is a key regulator of ploidy levels in Arabidopsis endoreduplication.
Plant cells frequently undergo endoreduplication, a process in which chromosomal DNA is successively duplicated in the absence of mitosis. It has been proposed that endoreduplication is regulated at its entry by mitotic cyclin-dependent kinase activity. 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 thaliana cyclin A gene, CYCA2;3, was revealed to be active in developing trichomes during the termination period of endoreduplication as well as in proliferating tissues. Taking advantage of the situation that plants encode highly redundant cyclin A genes, we were able to perform functional dissection of CYCA2;3 using null mutant alleles. Null mutations of CYCA2;3 semidominantly promoted endocycles and increased the ploidy levels achieved in mature organs, but they did not significantly affect the proportion of cells that underwent endoreduplication. Consistent with this result, expression of the CYCA2;3-green fluorescent protein fusion protein restrained endocycles in a dose-dependent manner. Moreover, a mutation in the destruction box of CYCA2;3 stabilized the fusion protein in the nuclei and enhanced the restraint. We conclude that CYCA2;3 negatively regulates endocycles and acts as a key regulator of ploidy levels in Arabidopsis endoreduplication.
Imai
Kumiko K
KK
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
Ohashi
Yohei
Y
Tsuge
Tomohiko
T
Yoshizumi
Takeshi
T
Matsui
Minami
M
Oka
Atsuhiro
A
Aoyama
Takashi
T
D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D016213:Cyclins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D020440:Gene Duplication; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D018515:Plant Leaves / Q000166:cytology / Q000648:ultrastructure; D018517:Plant Roots / Q000033:anatomy & histology / Q000166:cytology; D018520:Plant Shoots / Q000166:cytology; D030821:Plants, Genetically Modified / Q000033:anatomy & histology; D011003:Ploidies; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D036226:Seedlings / Q000033:anatomy & histology / Q000166:cytology; D013997:Time Factors
D029681:Arabidopsis Proteins; D016213:Cyclins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins