The miR159 family is an ancient microRNA (miRNA) that silences GAMYB family members throughout terrestrial plants. In Arabidopsis, miR159 can act as a molecular switch that completely suppresses the expression of MYB33 and MYB65 in vegetative tissues. Only in anthers and seeds is MYB33/65 expressed, where they participate in programmed cell death (PCD) of tapetal and aleurone cells. Recently, using MIMIC (MIM159) technology to transgenically suppress the function of miR159 in tobacco (Nicotiana tabacum) leads to widespread activation of GAMYB expression. This in turn resulted in up-regulation of genes associated with disease resistance and PCD, and immunity of the MIM159 tobacco plants to Phytophthora parasitica. However, from analogous MIM159 experiments in rice and Arabidopsis, it was unclear whether defence genes and immunity is activated upon miR159 inhibition. My project aims to elucidate the function of the highly conserved miR159-GAMYB pathway, and whether there are species-specific differences. Firstly, I will carry out RNA-seq on MIM159 plants of different species to obtain an understanding on which genes are differentially expressed upon miR159 inhibition. Secondly, I will set up a reporter gene system that detects activation of GAMYB expression to elucidate when this pathway becomes active in vegetative tissues. This uses the Arabidopsis CYS PROTEINASE1 (CP1), whose expression is tightly correlated with GAMYB expression. Both CP1-RUBY and CP1-GUS reporter genes will be transformed into Arabidopsis plants. These plant will be challenged will a variety of biotic/abiotic stresses and exogenous immune system triggers to determine when this pathway becomes active.