The Abc1 protein kinases are a large family of proteins involved in respiration in bacteria and mitochondria, even though, knowledge about their putative functions in chloroplasts is still limited. We carried out a functional characterization of AtSIA1, a chloroplast Arabidopsis thaliana Abc1-like protein, focusing on its potential redundancy with its homolog AtOSA1: A. thaliana knock-out mutant lines for AtSIA1 and AtOSA1 were considered and the double mutant was created. A reduction in content of plastidial iron and in the abundance of components of the Cytb6f complex were observed in mutants, suggesting that both AtSIA1 and AtOSA1 affect iron distribution within the chloroplast. Moreover, mutant plants accumulate more ferritin and superoxide than wild type plants, and their enhanced sensitivity to oxidative stress was supported by the upregulation of the antioxidant networks. Mutants produce altered levels of prenylquinones, but only atsia1 plants develop larger plastoglobules, containing higher levels of VTE1. Taken together, these data suggest that AtSIA1 and AtOSA1 may act as protein kinases in signaling pathways that influence plastidial responses to oxidative stress.
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