Arabidopsis photorespiratory serine hydroxymethyltransferase activity requires the mitochondrial accumulation of ferredoxin-dependent glutamate synthase.
The dual affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase for O(2) and CO(2) 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 CO(2), 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.
Jamai
Aziz
A
Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA.
Salomé
Patrice A
PA
Schilling
Stephen H
SH
Weber
Andreas P M
AP
McClung
C Robertson
CR
D000594:Amino Acid Oxidoreductases / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology; D012696:Glycine Hydroxymethyltransferase / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*
D029681:Arabidopsis Proteins; D002245:Carbon Dioxide; D000594:Amino Acid Oxidoreductases; C042233:glutamate synthase (ferredoxin); D012696:Glycine Hydroxymethyltransferase; C500791:SHMT1 protein, Arabidopsis