Restoration of fertility by antisense RNA in genetically engineered male sterile tobacco plants.

Transgenic tobacco plants (Nicotiana tabacum L.) expressing the rolC gene of Agrobacterium rhizogenes under the transcriptional control of the 35S RNA promoter are male sterile. When these plants are genetically crossed with others containing the rolC gene linked in antisense orientation to the 35S RNA promoter, hybrid progeny display restoration of male fertility. Moreover, hybrid progeny are revertant for other features of the rolC phenotype, such as restoration of plant height, leaf pigment content and female fertility. The level of restoration of the characteristics of untransformed tobacco appeared to be independent of the steady-state level of antisense RNA. Addition of six transcriptional enhancer sequences upstream of the 35S transcriptional start region in the antisense construct led to a higher steady-state level of antisense RNA than that produced using a promoter linked to a single enhancer sequence. However no significant difference was observed in the level of attenuation of the rolC phenotype in the progeny of crosses with either one or six transcriptional enhancers linked to the antisense rolC gene. Antisense constructs comprising only 189 bp of the rolC 5' coding region appeared less efficient in attenuating the rolC phenotype than those including the whole rolC coding region as well as its 3' untranslated region. Furthermore, results from experiments on light-controlled rolC gene expression indicate that microsporogenesis is sensitive to rolC gene action during the early stages of flower development.