Anthranilate synthase gene and method for increasing tryptophan production

Abstract

The present invention provides a method for conferring tolerance to an amino acid analog of tryptophan to a plant and/or altering the tryptophan content of a plant by introducing and expressing an isolated DNA segment encoding an anthranilate synthase in the cells of the plant. Transgenic plants transformed with an isolated DNA segment encoding an anthranilate synthase, as well as seeds and progeny derived from these plants, are also provided. The present invention also provides a cDNA sequence of an alpha and a beta subunit of a maize anthranilate synthase.

What is claimed is:  
     
         1 . A transgenic plant having increased levels of free L-tryptophan comprising endogenous DNA encoding native anthranilate synthase which is sensitive to inhibition by free L-tryptophan and exogenous DNA encoding exogenous anthranilate synthase which is resistant to inhibition by free L-tryptophan as compared to said native anthranilate synthase.  
     
     
         2 . A transformed plant of  claim 1  which is a monocot plant having free tryptophan at a level greater than 60 ppm.  
     
     
         3 . A transformed plant of  claim 1  derived from an untransformed plant wherein said free tryptophan content in the seed of said transformed plant is in the range of 1.1 to 50-fold higher than the tryptophan content in the seed of said untransformed plant.  
     
     
         4 . A transformed plant of  claim 1  which is a rice, rye, millet, wheat, barley, sorghum, maize or oat plant.  
     
     
         5 . A transformed plant of  claim 1  wherein said exogenous DNA is selected by screening an organism with a lethal quantity of an amino acid analog of tryptophan.  
     
     
         6 . A seed which can reproduce the transgenic plant of  claim 1 .  
     
     
         7 . A transgenic plant cell having increased levels of free L-tryptophan comprising endogenous DNA encoding native anthranilate synthase which is sensitive to inhibition by free L-tryptophan and exogenous DNA encoding exogenous anthranilate synthase which is resistant to inhibition by free L-tryptophan as compared to said native anthranilate synthase.  
     
     
         8 . A transformed plant cell of  claim 1  which is a rice, rye, millet, wheat, barley, sorghum, maize or oat plant cell.  
     
     
         9 . A transformed plant cell of  claim 1  wherein said exogenous DNA is selected by screening an organism with a lethal quantity of an amino acid analog of tryptophan.