Fusion of male-sterile tobacco causes modifications of mtDNA leading to changes in floral morphology and restoration of fertility in cybrid plants

Protoplasts from male-sterile Nicotiana tabacum cultivars with cytoplasms of N. suaveolens, N. bigelovii and N. undulata were fused in different pairwise combinations. Cybrid plants were obtained and categorized according to their flower morphologies into groups as parental male-sterile types, recombined biparentals, novel male-steriles and male fertiles. Restriction enzyme analyses and DNA gel blot hybridizations of the mitochondrial DNA (mtDNA) of these cybrid plants revealed that all plants with parental male-sterile morphologies had banding patterns identical to the parental patterns, whereas all cybrids with flower morphologies different from their parents had novel patterns. Several restriction fragments were found to be unique to the mtDNA of male-fertile plants with perfectly restored stamen morphologies when compared to the mtDNA from cybrid plants with incomplete restoration. MtDNA gel blot hybridization analysis of fertile plants revealed that the probe for atpA hybridized to two restriction fragments, one from each parent. Further, fertile plants with complete stamen restoration lacked an expressed sequence in the 3'flanking region of atpA , in contrast to both male-sterile parents.