Abstract
Phosphoenolpyruvate carboxylase (PEPC) undergoes activity regulation through reversible phosphorylation. Although the phosphorylation was considered to be enhanced by light in the leaves of C3 plants, we found that the maize PEPC expressed in transgenic rice leaves was phosphorylated at night. The phosphorylation was induced by nitrate addition irrespective of light conditions, and when grown with ammonium as a sole nitrogen source, the extent of phosphorylation did not show clear diurnal oscillation. These results suggest that the PEPC phosphorylation in rice leaves is not under the control of light but tightly correlates with the assimilation of nitrate. Expression analysis of three rice PEPC kinase genes (OsPPCK1-3) indicated that the expression of OsPPCK2 was induced by nitrate while that of OsPPCK3 was upregulated at night. We propose that OsPPCK2 and OsPPCK3 share roles in controlling the PEPC phosphorylation in rice leaves in response to physiological conditions.
