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© The Rockefeller University Press,
0021-9525/2000//369 $5.00
The Journal of Cell Biology, Volume 149, Number 2,
, 2000 369-378
Original Article |
A Small Chloroplast-Encoded Protein as a Novel Architectural Component of the Light-Harvesting Antenna
bock{at}biologie.uni-freiburg.de
A small conserved open reading frame in the plastid genome, ycf9, encodes a putative membrane protein of 62 amino acids. To determine the function of this reading frame we have constructed a knockout allele for targeted disruption of ycf9. This allele was introduced into the tobacco plastid genome by biolistic transformation to replace the wild-type ycf9 allele. Homoplasmic ycf9 knockout plants displayed no phenotype under normal growth conditions. However, under low light conditions, their growth rate was significantly reduced as compared with the wild-type, due to a lowered efficiency of the light reaction of photosynthesis. We show that this phenotype is caused by the deficiency in a pigment–protein complex of the light-harvesting antenna of photosystem II and hence by a reduced efficiency of photon capture when light availability is limiting. Our results indicate that, in contrast to the current view, light-harvesting complexes do not only consist of the classical pigment-binding proteins, but may contain small structural subunits in addition. These subunits appear to be crucial architectural factors for the assembly and/or maintenance of stable light-harvesting complexes.
Key Words: chloroplast • LHCII • light-harvesting complex • photosynthesis • ycf9
© 2000 The Rockefeller University Press
Abbreviations used in this paper: LHC, light-harvesting complex; LHCII, LHC of photosystem II; PSI, photosystem I; PSII, photosystem II; ptDNA, plastid DNA; RFLP, restriction fragment length polymorphism.
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