A CHIMERIC AND TRUNCATED MITOCHONDRIAL ATPA GENE IS TRANSCRIBED IN ALLOPLASMIC CYTOPLASMIC MALE-STERILE TOBACCO WITH NICOTIANA-BIGELOVII MITOCHONDRIA

Protoplast fusions were performed between two sexually produced allopl asmic male-sterile tobacco cultivars, with cytoplasms from Nicotiana b igelovii [Nta(big)S] and N. undulata [Nta(und)S], both of which exhibi t homeotic-like phenotypes affecting the petal and stamen whorls. Amon g the fusion products obtained, both novel male-sterile and pollen-pro ducing cybrid plants were identified. Of the pollen-producing cybrid p lants, all of which were indehiscent, some had flowers with stamens th at appeared normal when compared to male-fertile tobacco plants. Other hybrid plants were incompletely restored as they exhibited petaloid s tructures on the anther-bearing pollen-producing stamens. In this stud y, gel-blot analyses with mitochondrial gene-probes were conducted com paring the mitochondrial DNA of cybrids and male-sterile parents. It w as found that the flower morphology typical of the Nta(big)S parental plants, as well as of the novel male-sterile cybrids, coincided with t he presence of a chimeric atp A gene copy where an open reading frame of unknown origin was found to be linked in-frame to the 3'-end of a t runcated atp A gene. RNA gel-blot hybridizations revealed the presence of atp A transcripts in the male-sterile parent Nta(big)S and novel m ale-sterile cybrids, but which were absent in cybrids capable of polle n production.