Conservation of RNA editing between rice and maize plastids: are most editing events dispensable?

The extent of conservation of RNA editing sites in the plastid genome of ri ce was determined by comparing the genomic sequence with that of the cDNA. The presence of a T in the cDNA predicted to be a C by the DNA sequence of the plastid genome, indicated C to U editing. In the 11 plastid transcripts of rice a total of 21 editing sites were found. In maize, a closely relate d grass species, 26 editing sites have been reported in 13 plastid transcri pts. Most editing sites are conserved between the two species, although dif ferences in RNA editing were found at eight sites. In seven cases the T was already encoded at the DNA level, eliminating the requirement for RNA edit ing. In one case (rpoB, codon 206) the RNA sequence was conserved between t he two species, but the mRNA is still not edited in rice. It appears that, although evolutionarily conserved, RNA editing is essential only for a few plastid editing sites. Information about RNA editing ill rice plastids will facilitate the design of plastid vectors with broad applicability in grass species.