The VAR1 locus of Arabidopis encodes a choloroplastic 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 μmol/m²/s. Conclusion: 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.