Abstract
VAR1 and VAR2 are the ATP-dependent metalloproteases homologous to bacterial FtsH and located in thylakoid membranes in Arabidopsis. Loss of either protein in the mutant alleles leads to leaf variegation. Because the mutant leaves show a dramatic decrease of PSII activity under exposure to high light, both proteases are suggested to play a role in photoprotection of PSII. Despite the similarity between VAR1 and VAR2, a mutation at either one locus is not complemented by the function of the other, suggesting that there may be a communication mechanism. In fact , we found that VAR1 protein levels dramatically decrease not only invar2 mutants. Fractionation of thylakoid membranes by sucrose density gradient and blue-native gel analysis indicated that VAR1 forms an oligomer. Taken together, these results indicate that VAR1 and VAR2 form a hetero-complex and that loss of VAR1 leads to a selective degradation of VAR2 at the post-translational level.
