AtSIA1 AND AtOSA1: two Abc1 proteins involved in oxidative stress responses and iron distribution within chloroplasts

The Abc1 protein kinases are a large family of functionally diverse proteins with multipleroles in the regulation of respiration and oxidative stress tolerance. A functional characterization was carried out for AtSIA1, an Arabidopsis thaliana Abc1-likeprotein, focusing on its potential redundancy with its homolog AtOSA1. Both proteins arelocated within chloroplasts, even if a different subplastidial localization seems probable. Thecomparison of atsia1 and atosa1 mutants, atsia1/atosa1 double mutant and wild-type plantsrevealed a reduction in plastidial iron-containing proteins of the Cytb6f complex in themutants. Iron uptake from soil is not hampered in mutant lines, suggesting that AtSIA1 andAtOSA1 affect iron distribution within the chloroplast. Mutants accumulated more ferritin and superoxide, and showed reduced tolerance to reactiveoxygen species (ROS), potentially indicating a basal role in oxidative stress. The mutantsproduced higher concentrations of plastochromanol and plastoquinones than wild-typeplants, but only atsia1 plants developed larger plastoglobules and contained higher concentrationsof a- and c-tocopherol and VTE1. Taken together, these data suggest that AtSIA1 and AtOSA1 probably act in signaling pathwaysthat influence responses to ROS production and oxidative stress.