ABSTRACT
High-amylose starch is in great demand by the starch industry for its unique functional properties. However, very few high-amylose crop varieties are commercially available. Schwall et al. (2000) described the generation of very high-amylose starch containing potatoes by genetic modifi cation, by simultaneously inhibiting two isoforms of starch branching enzymes to below 1% of the wild-type activities. Starch granule morphology and composition were noticeably altered. Normal, high-molecular-weight amylopectin was absent, whereas the amylose content increased to levels comparable to the highest commercially available maize starch. In addition, the phosphorus content of starch also increased more than fi vefold. This unique starch with its high amylose, low amylopectin, and high phosphorus levels offers novel properties for food and industrial applications for potato as a crop. Though the production of high-amylose potato lines can be achieved by inhibition of two genes coding for starch branching enzymes, the use of antisense technology for gene inhibition has yielded a low frequency of high-amylose lines that mostly is correlated with high numbers of integrated T-DNA copies. To investigate whether production of high-amylose lines could be improved, RNA interference was used for inhibition of the genes Sbe1 and Sbe2 (Andersson et al., 2006). Two
constructs with 100 bp branching enzyme genes were cloned as inverted repeats controlled by a potato granule-bound starch synthase promoter. The construct pHAS3 is very effi cient, yielding high-amylose quality in more than 50% of the transgenic lines. An antisense construct resulted in only 3% of the transgenic lines of high-amylose type. It is also noticeable that pHAS3 yields low T-DNA copy inserts with an average of 83% of backbone-free transgenic lines being single copy events.
