Journal Article

Phosphoenolpyruvate carboxylase intrinsically located in the chloroplast of rice plays a crucial role in ammonium assimilation

Masumoto, Chisato, Miyao, Mitsue, Miyazawa, Shin-Ichi, Kusano, Miyako, Murayama, Seiji, Saito, Kazuki, Taniguchi, Yojiro, Ohkawa, Hiroshi, Fukuda, Takuya, Fukayama, Hiroshi

2010

Overview

Phosphoenolpyruvate carboxylase (PEPC) is a key enzyme of primary metabolism in bacteria, algae, and vascular plants, and is believed to be cytosolic. Here we show that rice (Oryza sativa L.) has a plant-type PEPC, Osppc4, that is targeted to the chloroplast. Osppc4 was expressed in all organs tested and showed high expression in the leaves. Its expression in the leaves was confined to mesophyll cells, and Osppc4 accounted for approximately one-third of total PEPC protein in the leaf blade. Recombinant Osppc4 was active in the PEPC reaction, showing Vmax comparable to cytosolic isozymes. Knockdown of Osppc4 expression by the RNAi technique resulted in stunting at the vegetative stage, which was much more marked when rice plants were grown with ammonium than with nitrate as the nitrogen source. Comparison of leaf metabolomes of ammonium-grown plants suggested that the knockdown suppressed ammonium assimilation and subsequent amino acid synthesis by reducing levels of organic acids, which are carbon skeleton donors for these processes. We also identified the chloroplastic PEPC gene in other Oryza species, all of which are adapted to waterlogged soil where the major nitrogen source is ammonium. This suggests that, in addition to glycolysis, the genus Oryza has a unique route to provide organic acids for ammonium assimilation that involves a chloroplastic PEPC, and that this route is crucial for growth with ammonium. This work provides evidence for diversity of primary ammonium assimilation in the leaves of vascular plants.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Algae / amino acid metabolism / Amino acids / Ammonium / ammonium nitrogen / Bacteria / Biological Sciences / carboxylic acids / Cells / Chloroplasts / Chloroplasts - enzymology / Chloroplasts - genetics / Enzymes / gene expression / Gene Knockdown Techniques / Genes, Plant / Kinetics / Leaf blade / Leaves / mesophyll / messenger RNA / Metabolism / Nitrogen / nitrogen metabolism / Organic acids / Oryza / Oryza - enzymology / Oryza - genetics / Oryza - growth & development / Oryza sativa / phosphoenolpyruvate carboxylase / Phosphoenolpyruvate Carboxylase - genetics / Phosphoenolpyruvate Carboxylase - metabolism / Plant Exudates - metabolism / Plant growth / Plant Leaves - cytology / Plant Leaves - metabolism / Plant Shoots - metabolism / Plants / Proteins / Quaternary Ammonium Compounds - metabolism / Recombinant Proteins - metabolism / Ribonucleic acid / Rice / RNA / Subcellular Fractions - metabolism / Xylem - metabolism