Abstract
Chloroplast biogenesis and development are highly complex processes requiring interaction between plastid and nuclear genomic products. Using a high-throughput screen for chloroplast biogenesis suppressors in Arabidopsis (Arabidopsis thaliana), we identified a suppressor of thf1 (sot5) that displays virescent and serrated leaves. Further characterization revealed that sot5 mutants are defective in leaf adaxial and abaxial polarity and act as enhancers of asymmetric leaves2 Map-based cloning identified SOT5 as a gene previously named EMB2279 that encodes a plastid-targeted pentatricopeptide repeat (PPR) protein with 11 PPR motifs. A G-to-A mutation in sot5 leads to a significant decrease in splicing efficiency, generating two additional mRNA variants. As reported previously, the sot5 null mutation is embryo lethal. SOT5 is predicted to bind to specific RNA sequences found in plastid rpl2 and trnK genes, and we found decreased splicing efficiency of the rpl2 and trnK genes in sot5 mutants. Together, our results reveal that the PPR protein SOT5/EMB2279 is required for intron splicing of plastid rpl2 and trnK, providing insights into the role of plastid translation in the coupled development between chloroplasts and leaves.
Highlights
Chloroplast biogenesis and development are highly complex processes requiring interaction between plastid and nuclear genomic products
We identified a pentatricopeptide repeat (PPR) protein, SOT5/ EMB2279, that is involved in the splicing of the plastid rpl2 and trnK introns
Since both Rpl2 and trnK are essential for plastid protein translation, complete disruption of SOT5 would lead to embryo lethality in Arabidopsis, similar to previously reported results for EMB2279 (Lurin et al, 2004; Cushing et al, 2005)
Summary
Chloroplast biogenesis and development are highly complex processes requiring interaction between plastid and nuclear genomic products. RNC1, which contains two RNase III domains without RNA cleavage activity, and WTF1, which has the plant organelle RNA recognition domain (PORR), form heterodimers that splice most of chloroplast group II introns in a CAF1/CAF2-dependent or -independent manner (Kroeger et al, 2009). It remains unclear whether a core spliceosome, as in the nucleus, is present for the in vivo splicing of all group II introns in chloroplasts
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