Comparison of a kanamycin versus hygromycin resistance gene in transgenic plant selection of Arabidopsis thaliana L

The neomycin phosphotransferase II (nptII) and hygromycin phosphotransferase II (hptII) genes, originally isolated from E. coli are widely used as selectable markers in transgenic research. The recovery of transgenic plants in the presence of respective selection agent has been greatly facilitated by these genes. The nptII gene confers transgenic plants resistance to the antibiotic, kanamycin, kan, and the hptII gene provides transgenic plants resistance to the antibiotic, hygromycin, hyg. 

These antibiotics normally inhibit protein synthesis in plants by binding to ribosomes. However, in the transgenic plants, the encoded enzymes, NPTII and HPTII catalyze the phosphorylation of kan and hyg respectively, once they enter into plant cells. The phosphorylated kan and hyg are inactive and therefore, unable to shut down the protein synthesis machinery in plants. This enables transgenic plants to grow in the presence of these antibiotics. Because there is no endogenous NPTII or HPTII activity in plants, these antibiotics can normally inhibit the growth of non-transgenic plants.