title: Increasing the carbohydrate storage capacity of plants by engineering a glycogen-like polymer pool in the cytosol.
abstract: Global demand for higher crop yields and for more efficient utilization of agricultural products will grow over the next decades. Here, we present a new concept for boosting the carbohydrate content of plants, by channeling photosynthetically fixed carbon into a newly engineered glucose polymer pool. We transiently expressed the starch/glycogen synthases from either Saccharomyces cerevisiae or Cyanidioschyzon merolae, together with the starch branching enzyme from C. merolae, in the cytosol of Nicotiana benthamiana leaves. This effectively built a UDP-glucose-dependent glycogen biosynthesis pathway. Glycogen synthesis was observed with Transmission Electron Microscopy, and the polymer structure was further analyzed. Within three days of enzyme expression, glycogen content of the leaf was 5-10 times higher than the starch levels of the control. Further, the leaves produced less starch and sucrose, which are normally the carbohydrate end-products of photosynthesis. We conclude that after enzyme expression, the newly fixed carbohydrates were routed into the new glycogen sink and trapped. Our approach allows carbohydrates to be efficiently stored in a new subcellular compartment, thus increasing the value of vegetative crop tissues for biofuel production or animal feed. The method also opens new potential for increasing the sink strength of heterotrophic tissues.
authors.affiliation: Institute for Agricultural Sciences, Plant Biochemistry, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: Simona
authors.initials: S
authors.lastname: Eicke
authors.affiliation: Institute for Agricultural Sciences, Plant Biochemistry, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Seung
authors.affiliation: Institute for Agricultural Sciences, Plant Biochemistry, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Egli
authors.affiliation: Institute for Agricultural Sciences, Plant Biochemistry, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: Emanuel A
authors.initials: EA
authors.lastname: Devers
authors.affiliation: Institute for Agricultural Sciences, Plant Biochemistry, ETH Zurich, CH-8092 Zurich, Switzerland. Electronic address: sstreb@ethz.ch.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Streb
mesh_terms: D050260:Carbohydrate Metabolism / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D024861:Genetic Enhancement / Q000379:methods*; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D060847:Metabolic Engineering / Q000379:methods; D053858:Metabolic Networks and Pathways / Q000235:genetics; D018515:Plant Leaves / Q000502:physiology*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism*; D013213:Starch / Q000235:genetics / Q000378:metabolism*; D014026:Nicotiana / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology
chemical_list: D013213:Starch; D006003:Glycogen; D005947:Glucose
keywords: Biofuel; Carbohydrate content; Glucose polymer biosynthesis; Glycogen; Pathway engineering