Higher levels of cell proliferation rate and cyclin CycD3 expression in the Arabidopsis amp1 mutant.

Cytokinins are involved in plant cell proliferation leading to plant growth and morphogenesis. The amp1 mutant of Arabidopsis has a five-fold higher l evel of cytokinin than the wild type plant. The mutant has a number of phen otypes with apparently increased cell proliferation rate similar to those s een in plants transformed with an ipt gene and having higher cytokinin leve ls. In order to identify molecular factors responsible for this cytokinin-i nduced higher cell division rate in the mutant we have examined cyclin gene s expression levels. While expression of the CycD1 and cycC cyclins is not altered or is slightly decreased in the mutant, cyclin CycD3, is more highl y expressed. The level of the CycD3 expression decreases in a "revertant" o f amp1, meaning that the over-expression of this particular cyclin is linke d to the phenotype of the amp1 mutant. Thus the expression of a specific G1 cyclin is upregulated in a mutant which has more cytokinin than the wild t ype.