THE PLANT CELL, Vol 3, Issue 10 1109-1120, Copyright © 1991 by American Society of Plant Biologists
Expression of the Wheat Mitochondrial nad3-rps12 Transcription Unit: Correlation between Editing and mRNA Maturation
J. M. Gualberto, G. Bonnard, L. Lamattina and J. M. Grienenberger
Institut de Biologie Moleculaire des Plantes du Centre National de la Recherche Scientifique, Universite Louis Pasteur, 12 rue du General Zimmer, 67084 Strasbourg Cedex, France
In plant mitochondria, RNA editing involves the conversion of cytidines in
the genomic DNA into uridines in the corresponding RNA. Analysis of cDNAs
prepared by reverse transcription of mitochondrial RNAs has shown that
partially edited RNAs are present in wheat mitochondria. The extent of this
partial editing as well as its potential influence on the corresponding
protein sequence were studied along with the expression of a wheat
mitochondrial locus. The sequence, expression, and RNA editing of the wheat
mitochondrial transcription unit containing four open reading frames (nad3,
rps12, orf299, and orf156), all cotranscribed into a same predominant
precursor RNA, have been studied. The product of orf156 is an 18-kD
mitochondrial membrane protein of unknown function, whereas the product of
orf299 could not be detected and this sequence seems to be a pseudogene.
Sequences of cDNA clones derived by the polymerase chain reaction technique
show that nad3, rps12, and orf156 transcripts are edited, whereas orf299 is
not edited, except for a sequence identical to part of the coxll gene.
Analysis of cDNA clones obtained from the precursor RNA shows the presence
of a large number of partially edited nad3-rps12 transcripts with no
evident polarity for the editing process. This shows that RNA editing is a
post-transcriptional event. In addition, study of partial editing at the
level of precursor, mature, and polysomal transcripts shows that mainly
mature, completely edited sequences are used for translation. Deletions of
a nucleotide at editing sites were observed in a number of cDNA clones,
suggesting that C->U RNA editing in plant mitochondria would be achieved
by nucleotide replacement.
