Reciprocal expression of two candidate di-iron enzymes affecting photosystem I and light-harvesting complex accumulation.
Crd1 (Copper response defect 1), which is required for the maintenance of photosystem I and its associated light-harvesting complexes in copper-deficient (-Cu) and oxygen-deficient (-O(2)) Chlamydomonas reinhardtii cells, is localized to the thylakoid membrane. A related protein, Cth1 (Copper target homolog 1), is shown to have a similar but not identical function by genetic suppressor analysis of gain-of-function sct1 (suppressor of copper target 1) strains that are transposon-containing alleles at CTH1. The pattern of Crd1 versus Cth1 accumulation is reciprocal; Crd1 abundance is increased in -Cu or -O(2) cells, whereas Cth1 accumulates in copper-sufficient (+Cu), oxygenated cells. This expression pattern is determined by a single trans-acting regulatory locus, CRR1 (COPPER RESPONSE REGULATOR 1), which activates transcription in -Cu cells. In +Cu cells, a 2.1-kb Cth1 mRNA is produced and translated, whereas Crd1 is transcribed only at basal levels, leading to Cth1 accumulation in +Cu cells. In -Cu cells, CRR1 function determines the activation of Crd1 expression and the production of an alternative 3.1-kb Cth1 mRNA that is extended at the 5' end relative to the 2.1-kb mRNA. Synthesis of the 3.1-kb mRNA, which encodes six small upstream open reading frames that possibly result in poor translation, blocks the downstream promoter through transcriptional occlusion. Fluorescence analysis of wild-type, crd1, and sct1 strains indicates that copper-responsive adjustment of the Cth1:Crd1 ratio results in modification of the interactions between photosystem I and associated light-harvesting complexes. The tightly coordinated CRR1-dependent regulation of isoenzymes Cth1 and Crd1 reinforces the notion that copper plays a specific role in the maintenance of chlorophyll proteins.
Moseley
Jeffrey L
JL
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
Page
M Dudley
MD
Alder
Nancy P
NP
Eriksson
Mats
M
Quinn
Jeanette
J
Soto
Feiris
F
Theg
Steven M
SM
Hippler
Michael
M
Merchant
Sabeeha
S
D020418:Algal Proteins / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000693:Anaerobiosis; D000818:Animals; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D003300:Copper / Q000172:deficiency; D019327:Copper Sulfate / Q000494:pharmacology; D004251:DNA Transposable Elements; D020224:Expressed Sequence Tags; D015870:Gene Expression; D005838:Genotype; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology; D018532:Pisum sativum / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics*; D010940:Plant Proteins; D012313:RNA / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013489:Suppression, Genetic; D020524:Thylakoids / Q000378:metabolism
D020418:Algal Proteins; D004251:DNA Transposable Elements; D010940:Plant Proteins; D012313:RNA; D003300:Copper; C409675:CRD1 protein, Chlamydomonas reinhardtii; D010088:Oxidoreductases; D019327:Copper Sulfate; D010100:Oxygen