High threonine producing lines of Nicotiana tobacum and methods for producing

A method for producing a modified tobacco plant line comprising an altered phenotype having an increase in at least one aspartate-derived branched amino acid selected from the group consisting of lysine, isoleucine, methionine, and threonine by selection for a mutation which results in the altered phenotype in the M1 generation, comprising the steps of:

• incubating seeds for the tobacco plant in a solution comprising a mutagen;
• washing the seeds free of the mutagen;
• germinating the seeds and growing M1 seedlings;
• adding a selection agent comprising lysine or threonine to the seedlings, wherein the selection agent selects for a chimeric plant, wherein the chimeric M1 plant at least partially comprises the altered phenotype of an increase in at least one aspartate-derived branched chain amino acid selected from the group consisting of lysine, isoleucine, methionine, and threonine;
• growing the M1 chimeric plant to generate M2 seeds, wherein the M2 seeds comprise non-mutagenized M2 seeds and mutagenized M2 seeds comprising the altered phenotype;
• and
• germinating the M2 seeds in a medium containing at least one selection agent comprising lysine or threonine to select for M2 plants comprising the altered phenotype of an increase in at least one aspartate-derived branched chain amino acid selected from the group consisting of lysine, isoleucine, methionine, and threonine.