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Physiol Plant. 2008 Jan;132(1):79-88. doi: 10.1111/j.1399-3054.2007.00995.x.

Maize D4;1 and D5 cyclin proteins in germinating maize. Associated kinase activity and regulation by phytohormones.

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1
Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, Avenida Universidad y Copilco, México D.F. 04510, México.

Abstract

We have previously reported the expression of four different maize D cyclins during seed germination and showed that cytokinins and auxins stimulate the expression of every cyclin in a differential way. In this paper we characterize the behavior at the protein level of two of these cyclins, CycD5 and CycD4;1. Antibodies were raised against CycD5;2 (which very likely also recognizes D5;1) and CycD4;1 and Western blot studies demonstrated that neither BA nor indol-3 acetic acid (IAA) stimulate cyclin accumulation during germination, compared with control levels. However, phytohormones, particularly IAA, modify the kinase activity associated to D cyclins preferentially at early hours of germination. The associated kinase moiety to D cyclins appears to be of a Cdk-A type because this protein immunoprecipitates with D cyclins and because kinase activity is strongly inhibited by both olomoucine and also by a peptide corresponding to the carboxy end of a maize kip related protein (KRP) protein. There is thus no correlation between mRNA and protein expression for these maize D cyclins during seed germination, although phytohormones may stimulate a signaling cascade that stimulates activation of protein kinase activity in cyclin-Cdk complexes.

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