Interaction of Nuclear and Mitochondrial Genomes in the Alteration of Maize Mitochondrial Orf221 Transcripts

The interaction of nuclear and mitochondrial genomes in the alteration of maize (Zea mays L.) mitochondrial orf221 transcript patterns was examined. Northern analyses involving specific maize nuclear genotypes associated with N, C or S cytoplasms revealed considerable orf221 transcript heterogeneity. F1 progenies were developed from maize inbred-cytoplasm combinations that differed for orf221 transcript patterns. Northern analyses revealed that the presence or level of abundance of certain orf221 transcripts was dependent on nuclear genotype. The maize inbred B37(C) exhibits orf221 transcripts of 3500, 3200, 2800, and 1300 nt whereas the F1 of B37(C) x Ky21(N) does not exhibit a 2800-nt transcript but does give transcripts of 2100 and 1250 nt in addition to 3500-, 3200- and 1300-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 A619 exhibits a 2300-nt orf221 transcript when associated with N cytoplasm and a 2100-nt orf221 transcript when associated with C and S cytoplasms. As a result of deletion of the gene T-urf13, the A188(T7) mitochondrial 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) x W64A(N)(2) gives a highly abundant 2100-nt orf221 transcript not detected in A188(T7). Deletion of T-urf13 has enabled the nuclear genotype of W64A(N) to alter orf221 transcript patterns in a manner not detected in T cytoplasm. This observation suggests that alteration of the mitochondrial genomic configuration adjacent to orf221 results in a different response to nuclear gene products from that observed when or2f21 is present in the T mitochondrial genome configuration.