Involved in the metabolism of all major classes of plastid RNAs. Required for efficient 3'-end processing of mRNAs and 3'-end maturation of rRNA transcripts, but is not sufficient to mediate their degradation. Mediates tRNA degradation. May function as a poly(A) mRNA 3'-5' degrading phosphorylase. May be required for plastid ribosome assembly and non-coding RNA biogenesis and accumulation. Seems not required for efficient translation. phosphate + RNA(n+1) = a ribonucleoside 5'-diphosphate + RNA(n) Delayed greening and retarded growth. Belongs to the polyribonucleotide nucleotidyltransferase family.