Several hundred nucleus-encoded factors are required for regulating gene expression in plant organelles.Among them, the most numerous are the members of the pentatricopeptide repeat (PPR) protein family. Wefound that PPR protein OTP82 is essential for RNA editing of the ndhB-9 and ndhG-1 sites within transcriptsencoding subunits of chloroplast NAD(P)H dehydrogenase. Despite the defects in RNA editing, otp82 did notshow any phenotypes in NDH activity, stability or interaction with photosystem I, suggesting that the RNAediting events mediated by OTP82 are functionally silent even though they induce amino acid alterations. Inagreement with this result, both sites are partially edited even in the wild type, implying the possibility that asingle gene produces heterogeneous proteins that are functionally equivalent. Although only five nucleotidesseparate the ndhB-8 and ndhB-9 sites, the ndhB-8 site is normally edited in otp82 mutants, suggesting thatboth sites are recognized by different PPR proteins. OTP82 falls into the DYW subclass containing conservedC-terminal E and DYW motifs. As in CRR22 and CRR28, the DYW motif present in OTP82 is not essential for RNAediting in vivo.