Cell-specific regulation of gene expression in mitochondria during anther development in sunflower.

Mitochondrial gene expression was characterized during meiosis in sunflower anthers. In situ hybridization experiments showed that there was a marked accumulation of four mitochondrial gene transcripts (atpA, atp9, cob, and rrn26) in young meiotic cells. This pattern of transcript accumulation was only detected for mitochondrial genes and not for transcripts of two nuclear genes (atpB and ANT) encoding mitochondrial proteins or another nuclear gene transcript (25S rRNA). Immunolocalization studies showed that the pattern of accumulation of the protein product of the atpA gene, the F1-ATP synthase alpha subunit, reflects that of the transcript. The expression of the novel mitochondrial orf522, which is associated with the cytoplasmic male-sterile (CMS) phenotype, was also studied by in situ hybridization. The orf522 transcripts were reduced in abundance in meiotic cells in the presence of fertility restorer genes. These results suggest that mitochondrial gene expression is regulated in a cell-specific fashion in developing anthers and that the restorer gene(s) may act cell specifically.