Abstract
Osppc4, a rice chloroplastic PEPC, is involved in a novel pathway of organic acid synthesis, which acts as a major route of carbon skeleton supply for the nitrogen assimilation in leaves. To understand functioning mechanisms of Osppc4 in the nitrogen assimilation, effects of ammonium addition to the culture solution on expression of genes for PEPCs and enzymes involved in ammonium assimilation were examined in leaves and roots.
In leaves, expression of Osppc4 and gln2 encoding GS2 was largely induced after the ammonium addition. Expression of Osppc2a and Osppc2b for cytosolic PEPCs was also enhanced, albeit to a lesser extent, while other genes did not show enhanced expression. In roots, by contrast, almost all genes examined showed enhanced expression. Among them, Osppc4 and Osppc1 for a major cytosolic PEPC most rapidly responded to the ammonium addition. The Osppc4 protein level was also increased concomitantly with induction of gene expression. These results suggest that Osppc4 acts to regulate ammonium assimilation by rapidly responding to ammonium status around roots.
