Poster: Cell Cycle & Cytokinesis

Abs # 1095: Characterization of cyclin-dependent kinases from maize endosperm

Presenter:	Dante, Ricardo A, rdante@ag.arizona.edu
Authors	Dante, Ricardo A (A)   Sabelli, Paolo A (A)   Leiva-Neto, Joao T (A)   Coelho, Cintia M (A)   Tao, Yumin  (B)   Gordon-Kamm, William  (B)   Larkins, Brian A (A)
Affiliations:	(A): Dept. of Plant Sciences, Forbes 303, University of Arizona, Tucson, AZ, 85721-0036 (B): Pioneer HiBred International, Inc., Johnston, IA, 50131-1004

Endoreduplication is proposed to increase the size, level of gene expression and metabolic activity of cells. In maize endosperm, endoreduplication initiates around seven to eight days after pollination, a period that coincides with the onset of starch and storage protein accumulation; hence, it is thought to influence the accumulation of these storage products. The cell cycle associated with endoreduplication in maize endosperm creates a reduction in mitotic cyclin-dependent kinase (CDK) activity and the up-regulation of S-phase CDKs. By over-expressing a dominant-negative mutant CDKA in transgenic maize endosperm, we caused a considerable reduction in endoreduplication and p13^suc1-adsorbed CDK activity. This suggests that CDKA activity is required for endoreduplication, although the nature of the cyclins directing this and other CDKs is unknown. To address this question, we characterized cyclins of different classes that are expressed in maize endosperm. These include two recently identified cyclin Ds, a cyclin A1, a cyclin B1 and a cyclin B2. Class-specific polyclonal antibodies that recognize these cyclins were generated and used to immunoprecipitate histone H1 kinase activity from developing endosperm. The analysis of these activities in wild type and the dominant-negative maize CDKA mutant will be reported.