OTP70 is a pentatricopeptide repeat protein of the E subgroup involved in splicing of the plastid transcript rpoC1

Abstract

SUMMARYOver 20 proteins of the pentatricopeptide repeat (PPR) family have been demonstrated to be involved in RNA editing in plant mitochondria and chloroplasts. All of these editing factors contain a so-called 'E' domain that has been shown to be essential for editing to occur. The presumption has been that this domain recruits the (unknown) editing enzyme to the RNA. In this report, we show that not all putative E-class PPR proteins are directly involved in RNA editing. Disruption of the OTP70 gene leads to a strong defect in splicing of the plastid transcript rpoC1, leading to a virescent phenotype. The mutant has a chloroplast transcript pattern characteristic of a reduction in plastid-encoded RNA polymerase activity. The E domain of OTP70 is not required for splicing, and can be deleted or replaced by the E domain from the known editing factor CRR4 without loss of rpoC1 splicing. Furthermore, the E domain of OTP70 is incapable of inducing RNA editing when fused to the RNA binding domain of CRR4. We conclude that the truncated E domain of OTP70 is no longer functional in RNA editing, and that the protein has acquired a new function in promoting RNA splicing.

A Putative Chloroplast Thylakoid Metalloprotease VIRESCENT3 Regulates Chloroplast Development in Arabidopsis thaliana

“…ys1 mutation causes an abolished RNA editing site in rpoB transcript, which may lead to defective plastid-encoded plastid RNA polymerase activities (17). Similarly, in otp70, the splicing of rpoC1 is compromised, which also leads to abnormal plastidencoded plastid RNA polymerase activities (18). In addition to these two categories of genes, virescent mutants have also been observed at rather high frequency in our screens for yellow variegated (var2) suppressors (19).…”

Disruption of a Rice Pentatricopeptide Repeat Protein Causes a Seedling-Specific Albino Phenotype and Its Utilization to Enhance Seed Purity in Hybrid Rice Production

“…Attempts to identify the in vivo RNA ligands have only been made for a few PPR proteins (Schmitz-Linneweber and Small, 2008;Okuda et al, 2009Okuda et al, , 2010Pfalz et al, 2009;Yu et al, 2009;Johnson et al, 2010;Chateigner-Boutin et al, 2011;Prikryl et al, 2011). Many of the postulated activities of PPR proteins still lack direct biochemical proof and thus leave open the possibility that their roles are more indirect than suspected and may require additional, unidentified factors.…”

A short PPR protein required for the splicing of specific group II introns in angiosperm chloroplasts

“…Although group II introns are considered to be ''self-splicing'' (Lambowitz and Zimmerly 2011), self-splicing has not been reported for any land plant chloroplast introns. In fact, 14 nuclear genes have been identified that are required for the splicing of group II introns in angiosperm chloroplasts (for review, see Falcon de Longevialle et al 2010;Chateigner-Boutin et al 2011;Watkins et al 2011). Each is required for the splicing of distinct, but overlapping intron subsets, and each intron has been shown to require multiple proteins.…”