Method for selecting transformed plant cells using ethionine and cystathionine gamma synthase as the selection agent and marker gene

Abstract

Disclosed are transgenic plants having edible portions that produce methional during processing. The plants contain increased methionine levels such that upon processing of the edible portion(s), methional levels are increased and lead to food products that possess improved flavor stability and/or quality. Plants of the Solanaceous family e.g., potato, tomato and eggplant, and other methional-producing plants including maize and soybean, are preferred plants. Several ways of genetically engineering plants to produce increased free Met levels are disclosed, with introduction of a non-native nucleic acid encoding cystathionine gamma synthase (CGS) and tissue-specific expression of an anti-sense S-adenosyl-methionine synthetase being preferred. Also disclosed are methods for selecting transformed plant cells using ethionine and CGS as the selection agent and marker gene respectively.

1 . A transgenic plant of the  Solanaceous  family comprising at least one non-native nucleic acid that when expressed in said plant results in increased free methionine levels relative to native free methionine levels.  
     
     
         2 . The transgenic plant of  claim 1  wherein said non-native nucleic acid encodes cystathionine gamma synthase (CGS).  
     
     
         3 . The transgenic plant of  claim 2  wherein said non-native nucleic acid encodes a wild-type  Arabidopsis  CGS.  
     
     
         4 . The transgenic plant of  claim 2  wherein said non-native nucleic acid encodes a mutant, non-self regulating  Arabidopsis  CGS.  
     
     
         5 . The transgenic plant of  claim 2  wherein said non-native nucleic acid is derived from a flowering plant, yeast or algae.  
     
     
         6 . The transgenic plant of  claim 5  wherein the non-native nucleic acid is derived from a plant that is potato, tomato, tobacco, ice plant or maize.  
     
     
         7 . The transgenic plant of  claim 2  wherein said non-native nucleic acid encodes a bacterial CGS.  
     
     
         8 . The transgenic plant of  claim 1  that is a potato and wherein said non-native nucleic acid comprises a tuber-specific promoter operably linked to an anti-sense S-adenosyl-methionine synthetase (SAMS) DNA.  
     
     
         9 . The transgenic plant of  claim 8  wherein the tuber-specific promoter is a patatin promoter.  
     
     
         10 . The transgenic plant of  claim 1  wherein said non-native nucleic acid comprises an anti-sense threonine synthase DNA.  
     
     
         11 . The transgenic plant of  claim 1  which is a potato plant.  
     
     
         12 . The transgenic plant of  claim 1  which is a tomato plant.  
     
     
         13 . Seed derived from the transgenic plant of  claim 1 .  
     
     
         14 . A transgenic plant comprising at least one non-native nucleic acid other than a nucleic acid that encodes a plant cystathionine gamma synthase, that is expressed in said plant and results in increased free methionine levels relative to native free methionine levels, wherein an edible portion of said transgenic plant contains increased methional levels when processed compared to methional levels in a processed edible portion obtained from a wild-type plant.  
     
     
         15 . The transgenic plant of  claim 14  that is a maize plant.  
     
     
         16 . The transgenic plant of  claim 14  that is a soybean plant.  
     
     
         17 . A method of making a plant having increased free methionine levels, comprising preparing a transgenic  Solanaceous  plant having a genome that contains a non-native nucleic acid molecule that is expressed in said plant and causes said plant to have increased free methionine levels compared to native free methionine levels.  
     
     
         18 . The method of  claim 17  comprising transforming a protoplast derived from a cell of a wild-type  Solanaceous  plant with the non-native DNA molecule to produce a transformed protoplast, and generating the transgenic plant from the transformed protoplast.  
     
     
         19 . The method of  claim 17  comprising introducing the non-native DNA molecule into tissue of a wild-type  Solanaceous  plant to produce transformed tissue, and regenerating the transgenic  Solanaceous  plant from the transformed tissue.  
     
     
         20 . A method of making a transgenic  Solanaceous  plant having enhanced flavor quality or stability, comprising preparing a transgenic  Solanaceous  plant having a genome that contains a non-native DNA molecule that is expressed in said plant and causes said plant to have increased free methionine levels compared to native free methionine levels, and wherein an edible portion of said transgenic plant when processed, contains increased methional levels relative to methional levels in a processed edible portion of a wild-type  Solanaceous  plant.  
     
     
         21 . The method of  claim 20  further comprising harvesting said transgenic plant and processing said edible portion of said transgenic plant.  
     
     
         22 . A processed product prepared by the method of  claim 21 .  
     
     
         23 . The processed product of  claim 22  comprising potato tuber.  
     
     
         24 . The processed product of  claim 22  comprising tomato fruit.  
     
     
         25 . A method of making a plant having increased free methionine levels, comprising preparing a transgenic plant having a genome that contains a non-native nucleic acid other than a nucleic acid encoding a plant cystathionine gamma synthetase molecule that is expressed in said plant and causes said plant to have increased free methionine levels compared to native free methionine levels and wherein an edible portion of said transgenic plant contains increased methional levels when processed compared to methional levels in a processed edible portion obtained from a wild-type plant.  
     
     
         26 . The method of  claim 25  comprising transforming a protoplast derived from a cell of a wild-type plant with the non-native DNA molecule to produce a transformed protoplast, and generating the transgenic plant from the transformed protoplast.  
     
     
         27 . The method of  claim 25  comprising introducing the non-native DNA molecule into tissue of a plant to produce transformed tissue, and regenerating the transgenic maize or soybean plant from the transformed tissue.  
     
     
         28 . A method of making a transgenic plant having enhanced flavor quality or stability, comprising preparing a transgenic plant having a genome that contains a non-native DNA molecule that is expressed in said plant and causes said plant to have increased free methionine levels compared to native free methionine levels, and wherein an edible portion of said plant when processed, contains increased methional levels relative to methional levels in a processed, edible portion of a wild-type plant.  
     
     
         29 . The method of  claim 28 , further comprising harvesting said transgenic plant and processing said edible portion of said transgenic plant.  
     
     
         30 . A processed product prepared by the method of  claim 29 .  
     
     
         31 . The processed product of  claim 30  comprising maize seed.  
     
     
         32 . The processed product of  claim 30  comprising soybean seed.