Nucleo-cytoplasmic interactions affect the 5' terminal transcription of mitochondrial genes between the isonuclear CMS line UG93A and its maintainer line UG93B of kenaf (Hibiscus cannabinus)

Gene expression and translation in plant mitochondria remain poorly understood due to the complicated transcription of its mRNA. In this study, we report the 5' and 3' RNA extremities and promoters of five mitochondrial genes, atp1, atp4, atp6, atp9, and cox3. The results reveal that four genes (atp1, atp4, atp6, and cox3) are transcribed from multiple initiation sites but with a uniform transcript at the 3' end, indicating that heterogeneity of the 5' end is a common feature in the transcription of kenaf mitochondrial genes. Furthermore, we found that the transcription initiation sites of these four genes are significantly different in UG93A, UG93B, and the F₁ hybrid. These data indicate that nuclear loci and unknown transcription factors within the mitochondria of different cytoplasmic types may be involved in mitochondrial transcription. Promoter architecture analysis showed that the promoter core sequences are conserved in the kenaf mitochondrial genome but are highly divergent, suggesting that these elements are essential for the promoter activity of mitochondrial genes in kenaf. Our results reveal that the heterogeneity of the 5' end and uniformity at the 3' end are common transcriptional features of mitochondrial genes. These data provide essential information for understanding the transcription of mitochondrial genes in kenaf and can be used as a reference for other plants.