Fe sparing and Fe recycling contribute to increased superoxide dismutase capacity in iron-starved Chlamydomonas reinhardtii.
Fe deficiency is one of several abiotic stresses that impacts plant metabolism because of the loss of function of Fe-containing enzymes in chloroplasts and mitochondria, including cytochromes, FeS proteins, and Fe superoxide dismutase (FeSOD). Two pathways increase the capacity of the Chlamydomonas reinhardtii chloroplast to detoxify superoxide during Fe limitation stress. In one pathway, MSD3 is upregulated at the transcriptional level up to 10(3)-fold in response to Fe limitation, leading to synthesis of a previously undiscovered plastid-specific MnSOD whose identity we validated immunochemically. In a second pathway, the plastid FeSOD is preferentially retained over other abundant Fe proteins, heme-containing cytochrome f, diiron magnesium protoporphyrin monomethyl ester cyclase, and Fe2S2-containing ferredoxin, demonstrating prioritized allocation of Fe within the chloroplast. Maintenance of FeSOD occurs, after an initial phase of degradation, by de novo resynthesis in the absence of extracellular Fe, suggesting the operation of salvage mechanisms for intracellular recycling and reallocation.
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
M Dudley
MD
Page
Michael D
MD
Allen
Janette
J
Kropat
Eugen I
EI
Urzica
Steven J
SJ
Karpowicz
Scott I
SI
Hsieh
Joseph A
JA
Loo
Sabeeha S
SS
Merchant
D000595:Amino Acid Sequence; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D045348:Cytochromes f / Q000378:metabolism; D005288:Ferredoxins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D007501:Iron / Q000378:metabolism*; D008969:Molecular Sequence Data; D013312:Stress, Physiological; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism*
D060365:Chloroplast Proteins; D005288:Ferredoxins; D045348:Cytochromes f; D006861:Hydrogen Peroxide; D007501:Iron; D013482:Superoxide Dismutase