Abstract:In this study, we identified a lowluminescence mutant referred to as rll4 (reduced LUC luminescence 4) by screening a M2 population derived from an ethyl methane sulfonate (EMS)mutagenized transgenic parental line ColLUC, which harbors a firefly luciferase reporter (LUC) gene under the control of 2×35S promoter. Genetic analysis demonstrated that the rll4 locus contains a single nuclearencoded recessive mutation. By using mapbased cloning strategy, we narrowed down the rll4 locus between the molecular markers CL417B10M1 and CL418B2M2, which are located at BAC (Bacterial Artificial Chromosome) clones F20D10 and F20M13 on chromosome 4, respectively. Methylationsensitive restriction enzyme PCR (ChopPCR) results showed the DNA methylation levels of a few genomic loci were increased in rll4 mutant. Reverse transcriptionPCR (RTPCR) results revealed that the expression levels of several endogenous targets of RNAdirected DNA methylation (RdDM) pathway were decreased in rll4 mutant while the expression of ROS1 (REPRESSOR OF SILENCING 1) remained unchanged. Taken together, these results suggest that RLL4 locus is probably involved in DNA demethylation process in A. thaliana.