INTERACTION OF NUCLEAR AND MITOCHONDRIAL GENOMES IN THE ALTERATION OFMAIZE MITOCHONDRIAL ORF221 TRANSCRIPTS

The interaction of nuclear and mitochondrial genomes in the alteration of maize (Zea mays L.) mitochondrial orf221 transcript patterns was e xamined. Northern analyses involving specific maize nuclear genotypes associated with N, C or S cytoplasms revealed considerable orf221 tran script heterogeneity. F-1 progenies were de veloped from maize inbred- cytoplasm combinations that differed for orf221 transcript patterns. N orthern analyses revealed that the presence or level of abundance of c ertain orf221 transcripts was dependent on nuclear genotype. The maize inbred B37(C) exhibits orf221 transcripts of 3 500, 3 200, 2 800, and 1 300 nt whereas the F-1 of B37(C)xKy21(N) does not exhibit a 2 800-n t transcript but does give transcripts of 2 100 and 1 250 nt in additi on to 3 500-, 3 200- and 1 300-nt transcripts, Northern analyses also suggested that the size or the presence of certain orf221 transcripts was related to the mitochondrial genome configuration. Maize inbred A6 19 exhibits a 2 300-nt orf221 transcript when associated with N cytopl asm and a 2 100-nt orf221 transcript when associated with C and S cyto plasms. As a result of deletion of the gene T-urf13, the A188(T7) mito chondrial mutant exhibits only a 3100-nt orf221 transcript and not the very complex T-urf13/orf221 transcript pattern associated with A188(T ). The genetic stock A188(T7)xW64A(N)(2) gives a highly abundant 2 100 -nt orf221 transcript not detected in A188(T7). Deletion of T-urf13 ha s enabled the nuclear genotype of W64A(N) to alter orf221 transcript p atterns in a manner not detected in T cytoplasm. This observation sugg ests that alteration of the mitochondrial genomic configuration adjace nt to orf221 results in a different response to nuclear gene products from that observed when orf221 is present in the T mitochondrial genom e configuration.