Gentamycin resistance in Nicotiana conferred by AAC(3)-I, a narrow substrate specificity acetyltransferase.

Abstract

Acetylation of the amino group in position 3 of the 2-desoxystreptamine moiety [AAC(3)] of gentamycin is a potent and wide-spread resistance mechanism in bacteria. Several marker genes coding for AAC(3) enzymes with varying substrate ranges or differing molecular properties have been identified. The enzymes AAC(3)-I and AAC(3)-II have a narrow substrate range and confer resistance to gentamycin and its close structural derivatives only, whereas genes encoding AAC(3)-III and AAC(3)-IV enzymes have a broad substrate range, modifying kanamycins, tobramycin, neomycin and paromomycin [1, 2]. Genes encoding AAC(3)-III and AAC(3)-IV enzymes were expressed in plants and shown to confer resistance to gentamicin, kanamycin (one of the genes), and possibly to other antibiotics [3]. Resistance to more than one antibiotic limits the use of the chimeric marker gene. We report that the narrow substrate range AAC(3)-I enzyme from the transposable element Tn21 [2] also provides a useful gentamycin resistance marker in plants. Materials and methods