Chemical genetics is a scientific strategy that utilizes bioactive small molecules as experimental tools to dissect biological processes. Bioactive compounds occurring in nature represent an enormous diversity of structures that potentially can be used as activators or inhibitors of biochemical pathways, transport processes, regulatory networks, or developmental programs. Screening methods to identify bioactive small molecules can vary greatly, ranging from visual evaluation of phenotypic alterations to quantifying biometric traits such as enzyme activities. Here, we describe a general methodology that permits identification of compounds modulating the expression of reporter genes in Arabidopsis thaliana seedlings. The selection of luciferase-based reporter systems has the advantage that it allows in vivo imaging of reporter gene activity in a semiquantitative manner without affecting plant viability. We chose an Arabidopsis line harboring the luciferase reporter under the control of the jasmonate-inducible LOX2 promoter to screen for either activators or inhibitors of gene expression. The outlined assay conditions can readily be applied to Arabidopsis lines containing other reporter genes. Thereby screening for small molecules affecting different signaling pathways and/or phenotypic responses is possible.