Regulation of endoreduplication in maize (Zea mays L.) endosperm. Isolation of a novel B1-type cyclin and its quantitative analysis.

To investigate the involvement of cyclin in mitotic and endoreduplicative cell cycle control, we have isolated a mitotic cyclin clone from a maize endosperm cDNA library. The deduced amino acid sequence of this clone identifies a novel B1-type cyclin with distinctly different sequence in regions with putative involvement in intracellular localization. This cyclin, designated Zeama;CycB 1;3 (CycZme1), was shown by RNA gel blots and quantitative RT-PCR to be specific for tissues engaging in cell proliferation. It accumulated in metaphase-arrested cells and declined rapidly upon release into G1 phase. During the transition from mitosis to endoreduplication in maize endosperm, CycZme1 transcript declined precipitously while transcripts associated with S phase (histone-H3 and PCNA) and multiple phases of the cell cycle (Cdc2, alpha-tubulin) remained at moderate to high levels. We conclude that CycZme1 down-regulation is involved in the cellular transition to endoreduplication.