Howard Paul Hershey

Isolation and characterization of cDNA clones for RNA species induced by substituted benzenesulfonamides in corn

A search of compounds capable of inducing specific gene expression in plants without affecting growth and development led to the examination of changes in the pattern of gene expression in corn after treatment with substituted benzenesulfonamide herbicide safeners. Following hydroponic treatment of corn with the safener N-(aminocarbonyl)-2-chlorobenzenesulfonamide (2-CBSU), the specific induction of new translatable mRNA species was observed. Replicate copies of a cDNA library made using RNA from 2-CBSU-treated corn roots were differentially screened with cDNA probes made from either the same mRNA fraction used for library construction or mRNA isolated from roots treated with 2-chlorobenzenesulfonamide (2-CBSA), an inactive analog of the safener. Colonies showing hybridization only with the probe made using mRNA from 2-CBSU-treated roots were further characterized to assess the specificity of the induction and decay of the corresponding induced RNA species. RNA blot analyses showed two clones, designated In2-1 and In2-2, contained plasmids that hybridized to RNAs that were induced from an undetectable background in corn roots within 30 minutes after treatment with 2-CBSU. Leaf and meristem tissues showed similar inductions of the In2-1 and In2-2 RNA species after a delay of several hours. In addition, both RNA species were induced in corn by foliar application of 2-CBSU. In contrast, neither RNA species was induced following stress treatments of plants. These results indicate a substituted benzenesulfonamide safener might be used with the promoters from the In2-1 and In2-2 genes to develop a new inducible gene expression system for plants.

The Use of Transgenic Plants to Study Phytochrome Domains Involved in Structure and Function

During the 30 years since its initial isolation, a great body of information has accumulated concerning the structure of phytochrome, the physiological responses it controls, and the genes whose expression it affects, yet little is known about the molecular mechanisms of phytochrome action. The recent advent of technologies allowing the expression of heterologous phytochrome genes in transgenic plants provide an important new method for research into the mechanisms of phytochrome action (Keller et al., 1989; Boylan and Quail, 1989; Kay et al., 1989). In the first report of this approach, Keller et al. (1989) described the expression of a functional oat phytochrome in tobacco. Transgenic plants expressing the oat protein have a radically altered phenotype characterized by decreased stem elongation, increased leaf chlorophyll content, reduced apical dominance, and delayed leaf senescence. Exploiting this “light-exaggerated” phenotype as an assay, it is now possible to identify and examine domains involved in phytochrome structure and function by in vitro mutagenesis.