Pesaresi P, Scharfenberg M, Weigel M, Granlund I, Schroder WP, Finazzi G, Rappaport F, Masiero S, Furini A, Jahns P, Leister D
Mutants, overexpressors, and interactors of Arabidopsis plastocyanin isoforms: Fevised roles of plastocyanin on photosynthetic electron flow and thylakoid redox state
Molecular Plant: 2009 2:236-248
Two homologous plastocyanin isoforms are encoded by the genesPETE1 and PETE2 in the nuclear genome of Arabidopsis thaliana.The PETE2 transcript is expressed at considerably higher levelsand the PETE2 protein is the more abundant isoform. Null mutationsin the PETE genes resulted in plants, designated pete1 and pete2,with decreased plastocyanin contents. However, despite reducingplastocyanin levels by over 90%, a pete2 null mutation on itsown affects rates of photosynthesis and growth only slightly,whereas pete1 knockout plants, with about 60–80% of thewild-type plastocyanin level, did not show any alteration. Hence,plastocyanin concentration is not limiting for photosyntheticelectron flow under optimal growth conditions, perhaps implyingother possible physiological roles for the protein. Indeed,plastocyanin has been proposed previously to cooperate withcytochrome c6A (Cyt c6A) in thylakoid redox reactions, but wefind no evidence for a physical interaction between the twoproteins, using interaction assays in yeast. We observed homodimerizationof Cyt c6A in yeast interaction assays, but also Cyt c6A homodimersfailed to interact with plastocyanin. Moreover, phenotypic analysisof atc6-1 pete1 and atc6-1 pete2 double mutants, each lackingCyt c6A and one of the two plastocyanin-encoding genes, failedto reveal any genetic interaction. Overexpression of eitherPETE1 or PETE2 in the pete1 pete2 double knockout mutant backgroundresults in essentially wild-type photosynthetic performance,excluding the possibility that the two plastocyanin isoformscould have distinct functions in thylakoid electron flow.
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