AN ALTERATION IN TRANSCRIPTION PATTERNS OF MITOCHONDRIAL GENES IN ALLOPLASMIC LINES OF BRASSICA-RAPA

The accumulation of transcripts of mitochondrial genes in young buds w as examined in euplasmic and alloplasmic lines of Brassica rapa for th e 'mur' system of cytoplasmic male sterility (CMS). Southern blotting analysis revealed the general absence of restriction fragment length p olymorphism between Diplotaxis muralis, the donor of cytoplasm, and ea ch of three sterile alloplasmic lines, indicating that the rearrangeme nt of mitochondrial DNA might not be caused by the nucleus of B. rapa. However, different Northern hybridization patterns were detected when coxI and nad3 were used as probes. Production of the 2.5-kb transcrip t of coxI and a reduction in levels of the transcript of nad3 in the s terile alloplasmic lines were clearly under the control of the nucleus of B. rapa. No such differences in patterns of transcripts were detec ted in the leaves. This observation suggests that some factor(s) or ge ne(s) in the nucleus of B. rapa. acts in an organ-specific manner to a lter the size of transcripts in the mitochondria of the donor cytoplas m without any structural changes in the mitochondrial genome. Further studies are required to clarify whether or not the unique transcripts in the young buds induce a CMS event.