Mapping and transcription studies have revealed that in Podospora anserina the causative agent of senescence, a mitochondrial plasmid (plDNA), is identical with intron 1 of the discontinuous gene for cytochrome-c-oxidase subunit 1 (COI), which is 2 kpb from the discontinuous gene for cytochrome b (Cytb). A mitochondrial mutant (ex1) devoid of the COI, but not of the Cytb gene provides longevity. A molecular model for the onset of senescence is presented.

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A AEMBL4 library of Triiicum aestivum mitochondrial (mt) DNA was constructed and probed with an oligonucleotide specific for subuinit 9 of pea mt F1-ATPase (atp9) (1) and with a probe for subunit a of Oenothera mt F1-ATPase (atpA) (2). Clones were isolated homologous with both the atpA and atp9 gene probes. Fig. 1 shows the organization of the atpA and atp9 genes on wheat mtDNA. Sequence analysis of a region spanning about 2.5 Kb revealed a sequence of 1527 bp encoding a polypeptide of 509 amino acids for the atpA gene and a sequence of 240 bp encoding a polypeptide of 80 amino acids for the atp9 gene (Fig. 2). Both genes are encoded by the same DNA strand. The sequences of the wheat atpA and atp9 genes share 93%, 98% and 93%, 97% hiomology witlh the corresponding genes from pea (4,1) ar,l maize (3,5). B e a S S a _ alpA Soo 6p atp, Fig. 1: Map of the Triticum mtDNA region carrying the atpA and the atp9 genes