Effect of plant WEE1 on the cell cycle and development in Arabidopsis thaliana and Nicotiana tabacum.

In eukaryotes the regulatory cell cycle gene, WEE1, encodes a protein kinase. In late G2, it inactivates cyclin-dependent kinase (CDKs) in the CDK-cyclinA/B complexes, by phosphorylating the CDK on tyrosine 15. This can result in a delay in mitosis. Expression of Arabidopsis thaliana homologue of WEE1 (AtWEE1) in fission yeast resulted in an elongated cell length phenotype in the same way as over expression of fission yeast wee1. I have tested whether AtWEE1 could also induce this effect in tobacco cells and Arabidopsis plant roots.

The tobacco BY-2 cells have been transformed with AtWEE1, both under constitutive and inducible promoters. Phenotypic characteristics observed compared with the control are premature entry into mitosis and a reduced cell size through a shortening of the G2 phase with a compensatory increase in the duration of G1 phase. Hence, the phenotype and cell cycle response is the exact opposite of the known effect of expression of this gene in fission yeast. NtWEE1 expression data revealed that the endogenous WEE1
expression is delayed in transgenic lines, this results in a non-inhibition of CDKA and CDKB1 which are already active in early S-phase.

AtWEE1 was also employed to transform Arabidopsis thaliana plants, both under constitutive and inducible promoters. The effect of AtWEE1 over expression was investigated on primary root growth and lateral root development. In particular, AtWEE1 over expression lead to less primary root growth and a reduction in the frequency of lateral root primordia initiated when compared with wild type. Arabidopsis transgenic plants initiated fewer primordia both per unit time and per cm of primary root.