Land Plant RNA Editing or: Don’t Be Fooled by Plant Organellar DNA Sequences

“It seems likely that most if not all the genetic information in any organism is carried by nucleic acid – usually by DNA […].” Plant organellar genomes have a spelling problem. If the genome were a book, many words with “U”s (uridines) would be spelled with “C”s (cytidines) instead, and in certain plant species, the reverse would also be seen, with Cs replaced by Us. However, plants change these “mistakes” at the RNA level, correcting U to C and C to U at non-random positions, via a phenomenon called RNA editing. We hope Francis Crick would have forgiven us for messing up the above quote from his 1962 Nobel Laureate acceptance speech. You can return the sentence to its original meaning easily by following the rules of plant organellar RNA editing. However, even when spelled right, the statement still has a hole in it, maybe one that Francis Crick anticipated and thus started the sentence with, “It seems likely….” Because here’s the rub: Organellar genetic information cannot be read the easy way, by identifying open reading frames based on start and stop codons and predicting the protein sequences based on codons. Instead, it is far better to read the RNA itself or, better yet in experimental terms, look at the cDNA.