Poster: Cell Cycle

Abs # 240: Functional aspects of the CycD3 family during tobacco development

Presenter:	Masubelele, Nompumelelo H, nhm22@biotech.cam.ac.uk
Additional Authors	Dewitte, Walter  (A)   Murray, James A H (A)
Affiliations:	(A): University of Cambridge, Institute of Biotechnology

D-type cyclins (CycD) were shown to play an important role and to transduce extracellular signals such as growth regulators at the G1/S transition of the cell cycle (Riou-Khamlichi et al., 1999). To investigate whether the different members of the tobacco CycD3 (Nicta; CycD3;1-4) family are regulated differentially during development, in situ hybridisations were used to elucidate their expression patterns. In addition, a dexamethasone inducible gene expression system was used to control their overexpression. By Northern blot, high CycD3 mRNA levels were found in proliferating tissues (vegetative and inflorescence tips), whereas low or no expression was observed in mature tissues (leaves and flowers). In situ hybridisation revealed that the cyclins mRNAs were uniformly distributed in the vegetative and inflorescence meristems, vascular tissues and in young reproductive organs. Striking differences were observed between CycD3;2, which was expressed thoughout the meristem and in leaf primodia, and CycD3;4 mRNA whose expression was restricted to the central region of the meristem. The different CycD3 members produced a gradient of similar phenotypes when overexpressed in tobacco. The phenotypes were characterised by elongated petioles, small leaves, cotyledons with altered shapes, and elongated sepals and petals. Detailed analysis showed that these phenotypes were caused by increased cell proliferation which correlated with a reduction of cells in the G1 phase of the cell cycle. A reduction of cell expansion, partial impairment of differentiation and loss of cellular organisation in the epidermis and vascular tissues was also observed. It can thus be proposed that although the expression of the CycD3 members is differentially controlled, their proteins could be to fulfilling the same and/or overlapping functions. Riou-Khamlichi, C., Huntley, R., Jacgumard, A. and Murray, J. A. H. (1999) Science, 283:1541-1544.