cdc2a expression in Arabidopsis is linked with competence for cell division.

A key regulator of the cell cycle is a highly conserved protein kinase whose catalytic subunit, p34(cdc2), is encoded by the cdc2 gene. We studied the control of the expression of the Arabidopsis cdc2a gene in cell suspensions and during plant development. In cell cultures, arrest of the cell cycle did not significantly affect cdc2a mRNA levels, but nutrient conditions were important for cdc2a expression. During plant development, the pattern of cdc2a expression was strongly correlated with the cell proliferation potential. The effects of external signals on cdc2a expression were analyzed. Wounding induced expression in leaves. Lack of light altered temporal regulation of cdc2a in the apical but not root meristem of seedlings. Differential cdc2a responses were obtained after different hormone treatments. Signals present only in intact plants were necessary to mediate these responses. Although other control levels have yet to be analyzed, these results suggest that the regulation of cdc2a expression may contribute greatly to spatial and temporal regulation of cell division in plants. Our results also show that cdc2a expression is not always coupled with cell proliferation but always precedes it. We propose that cdc2a expression may reflect a state of competence to divide, and that the release of other controls is necessary for cell division to occur.