The VAR1 locus of Arabidopsis encodes a chloroplastic FtsH and is responsible for leaf variegation in the mutant alleles.
BACKGROUND
A leaf-variegated mutation var1 of Arabidopsis results in the development of abnormal plastids and the formation of a green/white sector. Genetic analysis of the var1 mutant indicated that it acts synergistically with another mutation var2, suggesting that the two genes are relevant. The VAR2 locus has been shown to encode a chloroplastic FtsH, an ATP-dependent protease which is possibly involved in the degradation of thylakoid proteins and plastid development.


RESULTS
In this study we show that the VAR1 locus encodes a chloroplastic FtsH protein homologous to VAR2. VAR1 contains a conserved motif for ATPase and a metalloprotease characteristic to FtsH proteins, and is targeted into chloroplasts. A VAR1-fusion protein synthesized in vitro exhibited ATPase activity and partial metalloprotease activity. The maximum yield of photochemistry, measured by chlorophyll fluorescence, showed that the var1 mutants were sensitive to photoinhibitory light exposure at 800 micro mol/m2/s.


CONCLUSIONS
VAR1 and VAR2 comprise an FtsH small gene family together with other FtsH genes in Arabidopsis. VAR1 as well as VAR2 may play an important role in degrading photodamaged subunits in photosystem II. Loss of VAR1 and VAR2 perhaps impairs the photoprotection mechanism and thylakoid development, causing leaf variegation as a consequence.
Sakamoto
Wataru
W
Research Institute for Bioresources, Okayama University, Kurashiki, Okayama 710-0046, Japan. saka@rib.okayama-u.ac.jp
Tamura
Takayuki
T
Hanba-Tomita
Yuko
Y
Murata
Minoru
M
D049069:ATP-Dependent Proteases; D000483:Alleles; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002736:Chloroplasts / Q000235:genetics*; D017931:DNA Primers; D005453:Fluorescence; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics*; D008027:Light; D008565:Membrane Proteins / Q000235:genetics*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009154:Mutation; D018515:Plant Leaves / Q000378:metabolism; D018087:Plastids / Q000648:ultrastructure; D017386:Sequence Homology, Amino Acid
D049069:ATP-Dependent Proteases; D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D017931:DNA Primers; D019476:Insect Proteins; D008565:Membrane Proteins; C407423:VAR1 protein, Xenorhabdus nematophilus; C402651:AT2G30950 protein, Arabidopsis