Abstract
PEPC catalyzes the irreversible carboxylation of PEP to yield oxaloacetate and Pi. Although it has long been considered to be cytosolic, we recently found PEPC targeted to the chloroplast in rice (Osppc4). Genes encoding the chloroplastic isoform have been identified only in the genus Oryza, namely, in cultivated and wild rice species.
Osppc4 was expressed in all organs tested, exhibiting high expression in leaf blade and leaf sheath. Its expression was confined to green parenchymal cells in these organs. In contrast, it was expressed in vascular bundles in addition to green parenchymal cells in spikelet. Suppression of Osppc4 expression by RNAi technique led to 30-35% decrease of total PEPC activity of leaf blade, while the activity of spikelet remained almost unaffected. The suppression did not affect the photosynthetic rate but slightly inhibited growth during vegetative stage, while it significantly retarded grain filling and reduced grain yield.
