Scientists at the Max Planck Institute of Molecular Plant Physiology in Golm, Germany, have isolated a novel gene that is responsible for the phosphorylation of starch. The effects which occur if the expression of this gene is inhibited are described in the May issue of Nature Biotechnology.
Starch is composed of amylose and amylopectin, which are slightly or more highly branched glucose polymers. In addition, amylopectin can, depending on the plant organ where it is manufactured, contain different levels of phosphate monoesters. The phosphate content in potato tubers is exceptionally high as compared with other plant storage organs. Starch biosynthesis is accomplished by different forms of starch synthase which polymerize the glucose monomers using ADP-glucose, and isoforms of branching enzyme which introduce the branch points. Other enzymes are needed to determine the final starch structure, e.g. the presence of a debranching enzyme is a prerequisite to synthesize the semi-crystalline starch granules in contrast to non-crystalline glycogen, which accumulates in eukaryotes other than plants, in bacteria, or in mutants of different plant species lacking this enzyme.
Even though many starch biosynthetic enzymes are known, it has never been possible to
synthesize semi-crystalline glucans in vitro, nor has it been explained how the phosphate
monoesters are incorporated into starch. Furthermore, it is not clear at the moment which
enzymes are responsible for the breakdown of starch in vegetative plant organs. In order to
address these open questions in starch metabolism, researchers working in Jens Kossmanns in
the department headed by Lothar Willmitzer at the Max Planck Institute of Molecular Plan
Contact: Jens Kossmann