First published online July 22, 2005; 10.1104/pp.105.061234
Plant Physiology 138:1957-1966 (2005)
© 2005 American Society of Plant Biologists
BIOENERGETICS AND PHOTOSYNTHESIS
Functional Redundancy of AtFtsH Metalloproteases in Thylakoid Membrane Complexes1
Fei Yu,
Sungsoon Park and
Steven R. Rodermel*
Department of Genetics, Development, and Cell Biology, Iowa State University, Ames, Iowa 50011
FtsH is an ATP-dependent metalloprotease found in bacteria, mitochondria, and plastids. Arabidopsis (Arabidopsis thaliana) contains 12 AtFtsH proteins, three in the mitochondrion and nine in the chloroplast. Four of the chloroplast FtsH proteins are encoded by paired members of closely related genes (AtFtsH1 and 5, and AtFtsH2 and 8). We have previously reported that AtFtsH2 and 8 are interchangeable components of AtFtsH complexes in the thylakoid membrane. In this article, we show that the var1 variegation mutant, which is defective in AtFtsH5, has a coordinate reduction in the AtFtsH2 and 8 pair, and that the levels of both pairs are restored to normal in var1 plants that overexpress AtFtsH1. Overexpression of AtFtsH1, but not AtFtsH2/VAR2, normalizes the pattern of var1 variegation, restoring a nonvariegated phenotype. We conclude that AtFtsH proteins within a pair, but not between pairs, are interchangeable and functionally redundant, at least in part. We further propose that the abundance of each pair is matched with that of the other pair, with excess subunits being turned over. The variegation phenotype of var1 (as well as var2, which is defective in AtFtsH2) suggests that a threshold concentration of subunits is required for normal chloroplast function. AtFtsH1, 2, 5, and 8 do not show evidence of tissue or developmental specific expression. Phylogenetic analyses revealed that rice (Oryza sativa) and Arabidopsis share a conserved core of seven FtsH subunit genes, including the AtFtsH1 and 5 and AtFtsH2 and 8 pairs, and that the structure of the present-day gene families can be explained by duplication events in each species following the monocot/dicot divergence.
1 This work was supported by funding from the U.S. Department of Agriculture Competitive Research Grants Program (Biochemistry; grant no. 20013531810004 to S.R.R.) and from the U.S. Department of Energy, Energy Biosciences Panel (DE–FG02–94ER20147).
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.061234.
* Corresponding author; e-mail rodermel{at}iastate.edu; fax 515–294–1337.
Received February 15, 2005;
returned for revision April 28, 2005;
accepted May 11, 2005.
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