Fitness analyses of Arabidopsis thaliana mutants depleted of FtsH metalloproteases and characterization of three FtsH6 deletion mutants exposed to high light stress, senescence and chilling

Darwinian fitness analyses were performed, comparing single ftsh mutants with wild-type Arabidopsis thaliana plants grown under controlled laboratory conditions and in the field, by measuring plant size, survival rate, and silique and seed production. Additionally, three genotypes of Delta FtsH6 were analysed, under controlled growth conditions, with respect to both their ability to degrade the light-harvesting complex of photosystem II during senescence and light acclimation. In the field, substantial increases in variegation and reductions in growth were observed in the Delta FtsH2, Delta FtsH5 and Delta FtsH10 mutants; FtsH2 seemed particularly important for plant survival. Despite being grown in relatively cold weather, the Delta FtsH11 mutant displayed strong phenotypic deviations from wild type. Both Delta FtsH10 and Delta FtsH3 mutants exhibited less severe phenotypic changes, but were different from wild-type plants when placed in the field as young plants. When older Delta FtsH3 or Delta FtsH10 mutants were placed outdoors, no phenotypic differences from wild type were observed. Three genotypes of Delta FtsH6 displayed no phenotypic deviations from wild-type plants. Under controlled growth conditions, during senescence and light acclimation, no differences in the amount of chlorophyll or Photosystem II light-harvesting complex b3 (Lhcb3) were detected in Delta FtsH6 mutants compared with the wild type. Therefore, FtsH6 seems to be unimportant for LHCII degradation in vivo.