Many effector genes in M.oryzae are only expressed in plant tissue after invasive growth, and have very low expression in conidia and mycelium. We determined a workflow to screen mutants showing constitutive expression of fluorescence-labeled effector gene fusions in spores. By using quantitative imaging, bioinformatics analysis and genetic complementation, we elucidated that RGS1 (Regulator of G-protein Signalling 1) acts as a dominant transcriptional suppressor and governs a subset of effectors as a regulon in M.oryzae during the morphogenesis of appressorium maturation.