Methods for increasing starch content in plants

Abstract

Methods and compositions for increasing the starch content in green tissues of a plant are provided. The method comprises down-regulating me activity of starch degradation enzymes in a plant. The resulting transgenic plants of the invention have increased starch content in green tissues and exhibit a starch excess phenotype. In one embodiment the method involves manipulating a monocot plant to down-regulate the activity of a starch degradation enzyme. The plants are useful for improving the yield of free sugars from plant biomass and increase dried green tissue storage stability.

What is claimed is: 
     
         1 . A transgenic plant comprising a polynucleotide operably linked to a phosphoenol pyruvate carboxylase promoter, wherein expression of the polynucleotide inhibits or suppresses the expression in green tissues of one or more endogenous starch degradation enzymes selected from the group consisting of chloroplastic alpha amylase, glucan water dikinase, phosphoglucan water dikinase, limit dextrinase, isoamylase, chloroplastic beta-amylase, chloroplastic glucan phosphorylase, disproportionating enzyme, chloroplastic maltose transporter protein (Mex1), chloroplastic glucose transporter protein, and chloroplastic triose phosphate transporter protein, and the transgenic plant is one selected from the group consisting of maize, sugarcane, sorghum, millet, and switchgrass. 
     
     
         2 . An animal feed comprising a desiccated transgenic plant from one of maize, sugarcane, sorghum, millet, or switchgrass, wherein the transgenic plant comprises a polynucleotide operably linked to a phosphoenol pyruvate carboxylase promoter, and wherein expression of the polynucleotide inhibits or suppresses the expression in green tissues of one or more endogenous starch degradation enzymes selected from the group consisting of chloroplastic alpha amylase, glucan water dikinase, phosphoglucan water dikinase, limit dextrinase, isoamylase, chloroplastic beta-amylase, chloroplastic glucan phosphorylase, disproportionating enzyme, chloroplastic maltose transporter protein (Mex1), chloroplastic glucose transporter protein, and chloroplastic triose phosphate transporter protein. 
     
     
         3 . A method of preparing livestock feed comprising desiccating a transgenic plant comprising a polynucleotide operably linked to a phosphoenol pyruvate carboxylase promoter, wherein expression of the polynucleotide inhibits or suppresses the expression in green tissues of one or more endogenous starch degradation enzymes selected from the group consisting of chloroplastic alpha amylase, glucan water dikinase, phosphoglucan water dikinase, limit dextrinase, isoamylase, chloroplastic beta-amylase, chloroplastic glucan phosphorylase, disproportionating enzyme, chloroplastic maltose transporter protein (Mex1), chloroplastic glucose transporter protein, and chloroplastic triose phosphate transporter protein, and the transgenic plant is one selected from the group consisting of maize, sugarcane, sorghum, millet, and switchgrass. 
     
     
         4 . A nucleic acid comprising a polynucleotide operably linked to a phosphoenol pyruvate carboxylase promoter, wherein expression of the polynucleotide in a transgenic plant from one selected from the group consisting of maize, sugarcane, sorghum, millet, and switchgrass inhibits or suppresses the expression in green tissues of one or more endogenous starch degradation enzymes selected from the group consisting of chloroplastic alpha amylase, glucan water dikinase, phosphoglucan water dikinase, limit dextrinase, isoamylase, chloroplastic beta-amylase, chloroplastic glucan phosphorylase, disproportionating enzyme, chloroplastic maltose transporter protein (Mex1), chloroplastic glucose transporter protein, and chloroplastic triose phosphate transporter protein. 
     
     
         5 . An expression cassette for transformation of a plant from one of maize, sugarcane, sorghum, millet, or switchgrass, the expression cassette comprising a nucleic acid comprising a polynucleotide operably linked to a phosphoenol pyruvate carboxylase promoter, wherein expression of the polynucleotide in a transgenic plant from one of maize, sugarcane, sorghum, millet, or switchgrass inhibits or suppresses the expression in green tissues of one or more endogenous starch degradation enzymes selected from the group consisting of chloroplastic alpha amylase, glucan water dikinase, phosphoglucan water dikinase, limit dextrinase, isoamylase, chloroplastic beta-amylase, chloroplastic glucan phosphorylase, disproportionating enzyme, chloroplastic maltose transporter protein (Mex1), chloroplastic glucose transporter protein, and chloroplastic triose phosphate transporter protein.