A chloroplast-localized S1 domain-containing protein SRRP1 plays a role in Arabidopsis seedling growth in the presence of ABA.

Although the roles of S1 domain-containing proteins have been characterized in diverse cellular processes in the cytoplasm, the functional roles of a majority of S1 domain-containing proteins targeted to the chloroplast are largely unknown. Here, we characterized the function of a nuclear-encoded chloroplast-targeted protein harboring two S1 domains, designated SRRP1 (for S1 RNA-binding ribosomal protein 1), in Arabidopsis thaliana. Subcellular localization analysis of SRRP1-GFP fusion proteins revealed that SRRP1 is localized to the chloroplast. The T-DNA tagged loss-of-function srrp1 mutants displayed poorer seedling growth and less cotyledon greening than the wild-type plants on MS medium supplemented with abscisic acid (ABA), suggesting that SRRP1 plays a role in seedling growth in the presence of ABA. Splicing of the trnL intron and processing of 5S rRNA in chloroplasts were altered in the mutant plants. Importantly, SRRP1 complemented the growth-defective phenotypes of an RNA chaperone-deficient Escherichia coli mutant at low temperatures and had nucleic acid-melting ability, indicating that SRRP1 possesses RNA chaperone activity. Taken together, these results suggest that SRRP1, the chloroplast-localized S1 domain-containing protein, harboring RNA chaperone activity affects the splicing and processing of chloroplast transcripts and plays a role in Arabidopsis seedling growth in the presence of ABA.