The XXXX FtsH metalloprotease gene family: interchangeability of subunits in chloroplast oligomeric complexes.

@entity20267 @entity72611 @entity72610 @entity958 @entity20268 @entity72613 @entity72612
The @entity958 At filamentation temperature sensitive (FtsH) metalloprotease gene family comprises 12 members ( @entity72610 -AtFtsH12), including three pairs of closely related genes that are targeted to chloroplasts ( @entity20267 and @entity72611 ; @entity72610 and @entity20268 ; and @entity72612 and @entity72613 ). Mutations in @entity20268 ( @entity20268 ) and @entity20267 ( @entity20267 ) give rise to variegated plants with green- and white-sectored leaves. Cells in the green sectors contain morphologically normal chloroplasts, whereas cells in the white sectors are blocked in chloroplast biogenesis. A major question is how chloroplasts arise in cells that have a mutant genotype. We have found by two-dimensional (2-D) green gel and gel filtration analyses that @entity20267 / @entity20267 forms oligomeric complexes. Two bands in the 2-D green gels that correspond to @entity20268 / @entity20268 + @entity72610 and @entity20267 / @entity20267 + @entity72611 have been identified, and these bands are coordinately reduced in amount in @entity20268 and @entity20267 thylakoids that lack @entity20268 / @entity20268 and @entity20267 / @entity20267 , respectively. These reductions are not because of alterations in transcript abundance. Overexpression of @entity72611 in @entity20267 -4 (a putative null allele) normalizes the variegation phenotype of the mutant and restores the two bands to their wild-type levels. These results suggest that @entity72611 is interchangeable with @entity20267 / @entity20267 in AtFtsH-containing oligomers, and that the two proteins have redundant functions. Consistent with this hypothesis, @entity20267 and @entity72611 have similar expression patterns, as monitored by promoter-beta-glucuronidase (GUS) fusion and RT-PCR experiments. Based on our findings, we propose that @entity72610 , @entity20267 / @entity20267 , @entity20268 / @entity20268 , and @entity72611 interact to form oligomeric structures, and that subunit stoichiometry is controlled post-transcriptionally in @entity20268 and @entity20267 , perhaps by turnover. A threshold model is presented to explain the pattern of variegation in @entity20267 in which @entity72611 provides a compensating activity in the green sectors of the mutant.
