An Efficient Procedure for Protoplast Isolation from Mesophyll Cells and Nuclear Fractionation in Rice Plant protoplasts, a proven physiological and versatile cell system, are widely used in high-throughput analysis and functional characterization of genes. Green protoplasts have been successfully used in investigations of plant signal transduction pathways related to hormones, metabolites and environmental challenges. This protocol, adapted from Zhang et al. (2011), describes a procedure for the isolation of rice protoplasts from green tissue and shows an efficient and rapid method for isolation of nuclei form these protoplasts which are commonly used in a variety of experimental procedures including the isolation of high-molecular-weight DNA (Watson and Thompson, 1986), in vitro DNA synthesis (Roman, 1980), isolation of labeled transcripts for differential screening of cDNA libraries (Somssich et al., 1989), preparation of nuclear extracts for in vitro transcription systems (Roberts and Okita, 1991), isolation of nuclear proteins (Harrison et al., 1992) and studies of protein targeting to the nucleus (Hicks and Raikhel, 1993).