No abstract

Most plant viruses are transmitted by insect vectors. We present an alternative method for the introduction of infectious viral DNA that uses the ability of Agrobacterium to transfer DNA from bacterial cells to plants. Cauliflower mosaic virus was chosen to develop this method because it is the best characterized plant DNA virus and can be introduced into plants via aphids, virus particles, viral DNA, or suitably treated cloned DNA. We show that systemic infection of turnips results from wounding and inoculation with strains of Agrobacterium tumefdciens in which more than one genome of cauliflower mosaic virus have been placed tandemly in the T-DNA of thO tumor-induiheg plasmid. Thus such constructions allow escape of the viral genome from the T-DNA once inside the plkuts. The combined use of the tumor-inducing plasmid and viral DNA opens the way to molecular biological approaches that are not possible with either system alone.

A transferred DNA (T-DNA) tagging vector with the potential to produce dominant mutations was used with cocultured Agrobacterium tumefaciens and protoplasts to tag genes involved in the action of the plant growth substance auxin. Transgenic calli were selected for their ability to grow in the absence of auxin in the culture media. From one experiment, 12 calli that displayed this phenotype were recovered, of which 11 were able to regenerate into plants. In one plant studied in detail, protoplast division in the absence of auxin genetically cosegregated with a single T-DNA insert. A messenger RNA encoded by a 6.4-kilobase sequence of plant genomic DNA rescued from the mutant is overexpressed relative to untransformed plants. The genomic DNA, as well as a cognate complementary DNA, once transfected into protoplasts promote growth and cell division in vitro in the absence of exogenously added auxin.

The gene ENOD40 is expressed during early stages of legume nodule development. A homolog was isolated from tobacco, which, as does ENOD40 from legumes, encodes an oligopeptide of about 10 amino acids. In tobacco protoplasts, these peptides change the response to auxin at concentrations as low as 10(-12) to 10(-16)M. The peptides encoded by ENOD40 appear to act as plant growth regulators.

No abstract