Methylation of mitochondrial DNA in carrot (Daucus carota L.)

The methylation status of carrot (Daucus carota L.) mitochondrial DNA (mtDNA) was studied using isoschizomeric restriction enzymes MspI/HpaII (CCGG) and MvaI/EcoRII [CC(A/T)GG]. Southern hybridisations with probes for mitochondrial genes coxII and atpA were performed. MtDNAs isolated from non-embryogenic cell suspensions and roots were analysed. No differences were found using MspI/HpaII but after digesting the mtDNA with MvaI and EcoRII, some qualitative and quantitative differences between the restriction patterns appeared. Distinction was also revealed after Southern hybridisation with the coxII probe. These data indicate that the mtDNA of carrot is methylated in CNG trinucleotides and unmethylated in CG dinucleotides in CCGG sequences. The results were reproducible for cell suspensions of various genotypes and even cultivars but the extent of methylation was different in the root. The possible role of methylation in the mitochondrial genome of higher plants is discussed.