The highly conserved microR159 (miR159) has been widely studied in multiple, diverse plant species, however, no clear conserved functional role has been identified. It acts as a genetic switch, specifically silencing the expression of a family of regulatory GAMYB genes that encode R2R3 MYB domain transcription factors. Inhibiting miR159 in Arabidopsis, tobacco (Nicotiana tabacum and Nicotiana benthamiana) and Oryza sativa, through constitutive expression of a MIM159 target mimic transgene, resulted in the de-repression of GAMYB expression in all species. This had a strong negative impact on growth and development, resulting in stunted growth in all these species. In Nicotiana tabacum, RNA-seq analysis found that genes corresponding to a strong and broad defense response was strongly induced, and consistently these MIM159 N. tabacum plants appeared highly resistant to a major pathogen, Phytophthora parasitica. However, whether resistance was due to the upregulated defence pathways, or as a result of the dwarf stature needed resolving. Therefore, I am developing transgenic systems to inhibit miR159 transiently, via the expression of an inducible MIM159 transgene, or an inducible GAMYB gene that is resistant to miR159 silencing using the inducible XVE promoter which only allows expression in the presence of estradiol. I will report progress on my experiments.