Transgenic sugar beet tolerant to glyphosate

Sugar beet (Beta vulgaris L.) lines transformed with the 5-enolpyruvylshikimate-3-phosphate synthase gene (CP4 EPSPS) from Agrobacterium sp. CP4 and a glyphosate oxidase reductase gene (GOX) also isolated from bacteria resulted in the development of lines highly tolerant to glyphosate. Glyphosate (N-phosphonomethyl-glycine) is the active ingredient in Roundup®, herbicide. The EPSPS enzyme is involved in the biosynthesis of aromatic amino acids. Glyphosate binds irreversible to the EPSPS and inhibits the pathway. GOX degrades glyphosate into non-toxic compounds. 260 independent transformants have been evaluated in greenhouse and field trials for tolerance to Roundup® in 1993 and 1994. Variation of tolerance was recorded between different transformants, ranging from complete susceptibility to full tolerance. The Agrobacterium tumefaciens mediated transformation resulted in a negative correlation between copy number of the T-DNA insert and the level of tolerance to the herbicide. Transformants which contain a single copy insert showed tolerance to higher doses of glyphosate than transformants with multiple copies. Two transgenic lines were identified that showed agronomically useful tolerance to glyphosate.[PUBLICATION ABSTRACT]