Starch is an important industrial raw material both for food and non-food purposes. In plants, starch is deposited in the leaf and in the storage tissues such as seed endosperm, roots or tubers. Starch is a glucose polymer, and its synthesis involves four groups of enzymes, ADP-glucose-pyrophosphorylase (AGPase), starch synthases (SS), starch branching enzymes (SBE), and starch debranching enzymes (DBE). In barley, four isoforms of SBE have been identified and the temporal and spatial expression of their genes (sbe) has been studied in our lab.

The long-term objective of our research is to produce novel starches in planta for industrial applications. This requires the transformation of barley in order to produce transgenic plants with altered activity for one or more sbe genes. Using a plant-optimized version of Green Fluorescent Protein (GFP) as the only marker we produced a transgenic Nordic elite cultivar of barley in 1999. The usefulness of GFP as a marker has also been applied in various transient experiments and for this reason a set of monocotyledonous expression vectors has been developed. Using these vectors, the spatial expression pattern of the sbeII genes has been investigated.

The sbeIIa and sbeIIb genes are differentially transcribed during barley seed development. The sbeIIb gene is expressed exclusively in the endosperm while the sbeIIa gene is expressed also in embryonic and vegetative tissues. The tissue specific regulation of the sbeII genes was hown to be executed via a repressor protein acting on a cis element located in the second intron of the sbeIIb gene. We also suggest that the repression is controlled by the local sugar concentration in the barley seed endosperm.