THE PLANT CELL, Vol 3, Issue 12 1363-1378, Copyright © 1991 by American Society of Plant Biologists

RESEARCH ARTICLES

A trans-Splicing Model for the Expression of the Tripartite nad5 Gene in Wheat and Maize Mitochondria

A. P. de Souza, M. F. Jubier, E. Delcher, D. Lancelin and B. Lejeune
Laboratoire de Biologie Moleculaire Vegetale associe au Centre National de la Recherche Scientifique, UA 1128, Batiment 430, Universite Paris XI, 91405 Orsay Cedex, France

The mitochondrial single-copy gene nad5 of wheat and maize consists of 5 exons located on three widely separated regions of the genome that are independently transcribed. The first region contains exons I and II separated by an atypical group II intron; in the second region is exon III (only 22 bp long), which is flanked upstream by a maturase-related open reading frame (ORF) and exon e of the nad1 gene, and downstream by a previously unidentified ORF (ORF143); in the third region are exons IV and V separated by a group II intron. In maize, this last domain is flanked upstream by the genes rps12, nad3, and tRNASer and downstream by a chloroplast tRNACys. RNA editing occurs in wheat exons IV and V as C-to-U changes. A detailed analysis of the transcription of the nad5 gene in wheat and maize reveals that the exons are assembled into a 2.4-kb mRNA after two cis-splicing (between exons I and II and exons IV and V) and two trans-splicing events. The trans-splicing process involves the sequences flanking exons II, III, and IV that feature group II introns. A model is proposed for the assembly and maturation of the nad5 transcripts.

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