Programmed cell death (PCD) is the process when particular cells or tissues die as a part of normal development, which means that the whole process is controlled by the plant itself. In plants PCD is critical in for example formation of the hollow vessels in the vascular system. A group of proteins called metacaspases are believed to play a pivotal role in PCD in plants. As metacaspase 9 have been shown to be upregulated in Populus during xylem maturation this study attempted to locate those genes affecting its expression in Arabidopsis by forward genetics using a reporter line with green fluorescent protein (GFP) fused to the promoter of metacaspase 9. Ethyl methanesulfonate seed mutagenesis was used to generate mutants that were screened searching for plants with a GFP pattern deviating from that found in the reporter line. Mutations could then be located through mapping and deep sequencing resulting in candidate genes that could potentially be involved in regulating the expression of metacaspase 9.