Transient expression of anthocyanin genes in barley epidermal cells: Potential for use in evaluation of disease response genes

A transient assay is described that should allow evaluation of the role of host genes in disease response by enhancing or disrupting expression of those genes in specific cells and looking for effects on disease development. The assay also has the potential for assessing utility of host and non-host genes in enhancing resistance to disease in transgenic plants. Particle bombardment with a helium discharge particle gun was utilized to transiently express genes in epidermal cells of coleoptiles of barley (Hordeum vulgare). An anthocyanin reporter gene construct provided a means of identifying those cells that were transiently expressing introduced DNA. Optimal transient expression rates were achieved two days following bombardment with 1800 psi helium pressure, 1.0 mu m diameter gold particles, and coleoptile pre- and post-treatment in 0.30-0.35 M mannitol/sorbitol. Under optimal conditions, at least 35 cells expressed anthocyanin per bombardment. Transiently expressing cells were inoculated with the fungal pathogen, Erysiphe graminis f. sp. hordei, and fungal development observed. Neither the bombardment procedures, the presence of nearby dead cells, nor accumulation of anthocyanin within living cells affected fungal development in living cells. Therefore, incorporation of disease-related genes onto the same plasmid as the reporter genes will allow evaluation of the role of those genes in disease development or suppression. Since particle bombardment is possible with a great range of different plant tissues, the described methodology should exhibit wide applicability for evaluating genes in diverse plant-pathogen interactions, as well as genes involved in many other biological processes.