Arabidopsis Photorespiratory Serine Hydroxymethyltransferase Activity Requires the Mitochondrial Accumulation of Ferredoxin-Dependent Glutamate Synthase

• Published in: The Plant cell Vol. 21; no. 2; pp. 595 - 606
• Main Authors: Jamai, Aziz, Salomé, Patrice A, Schilling, Stephen H, Weber, Andreas P.M, McClung, C. Robertson
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 01.02.2009
• Subjects: Amino Acid Oxidoreductases - metabolism; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Carbon Dioxide - metabolism; Chloroplasts; Chloroplasts - enzymology; Fluorescence; Genetic mutation; Glycine Hydroxymethyltransferase - genetics; Glycine Hydroxymethyltransferase - metabolism; Hypochromic anemia; Mitochondria; Mitochondria - enzymology; Photorespiration; Plant cells; Plants; Proteins; Protoplasts
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.108.063289

The dual affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase for O₂ and CO₂ results in the net loss of fixed carbon and energy in a process termed photorespiration. The photorespiratory cycle is complex and occurs in three organelles, chloroplasts, peroxisomes, and mitochondria, which necessitates multiple steps to transport metabolic intermediates. Genetic analysis has identified a number of mutants exhibiting photorespiratory chlorosis at ambient CO₂, including several with defects in mitochondrial serine hydroxymethyltransferase (SHMT) activity. One class of mutants deficient in SHMT1 activity affects SHM1, which encodes the mitochondrial SHMT required for photorespiration. In this work, we describe a second class of SHMT1-deficient mutants defective in a distinct gene, GLU1, which encodes Ferredoxin-dependent Glutamate Synthase (Fd-GOGAT). Fd-GOGAT is a chloroplastic enzyme responsible for the reassimilation of photorespiratory ammonia as well as for primary nitrogen assimilation. We show that Fd-GOGAT is dual targeted to the mitochondria and the chloroplasts. In the mitochondria, Fd-GOGAT interacts physically with SHMT1, and this interaction is necessary for photorespiratory SHMT activity. The requirement of protein-protein interactions and complex formation for photorespiratory SHMT activity demonstrates more complicated regulation of this crucial high flux pathway than anticipated.