Reporter genes are widely used for studying the expression of foreign genes in transformed plants tissues. Using appropriate promoter-reporter gene constructs, this technique allows an independent verification of the transformed status of tissues growing on media containing selective antibiotics or herbicides. In addition, it serves as a principal means to follow gene transfer and monitor genetic transformation of plant species. Encoded by the E. coli GUS gene (also referred to as uidA), GUS protein is a hydrolase that catalyses the cleavage of a variety of beta-glucuronide derivatives available for colorimetric, fluorimetric and histochemical assays. Several features make the gus gene superior as a reporter gene for plant studies and in the production of genetically engineered crops.