Selectable marker genes can be divided into several categories depending on whether they confer positive or negative selection and whether selection is conditional or non-conditional on the presence of external substrates.Green fluorescent protein(GFP),β-galactosidase(GAL),luciferase(LUC),β-glucuronidase(GUS),and oxalate oxidase (OxO) have been important in transgenic plant research or crop development,and have been assessed for efficiency,biosafety,scientific application and commercialization. Despit...