Duplication and suppression of chloroplast protein translocation genes in maize

The HCF106 (high chlorophyll flourescence) gene of maize encodes a chloropl ast membrane protein required for tr,translocation of a subset of proteins across the thylakoid membrane. Mutations in HCF106 caused by the insertion of Robertson's Mutator transposable elements have been mapped to chromosome 2S. Here we show that there is a closely related homolog of HCF106 encoded elsewhere in the maize genome (HCF106c) that can partially compensate fur these mutations. This homolog maps on chromosome 10L and is part of the mos t recent set of segmental duplications in the maize genome. Triple mutants that are disrupted in both the HCF106 and Sec-dependent protein translocati on pathways provide evidence that the act independently. The HCF106c gene a ccounts for a previously reported exception to the correlation between epig enetic suppression of hcf106 and methylation of Mutator transposons. We als o demonstrate that insertions of Robertson's Mutator elements into either i ntrons or promoters can lead to mutations whose phenotypes are suppressed i n the absence of Mu activity, while alleles with insertions in both positio ns are not suppressed. The implications of these observations are discussed .