High level fructan accumulation in a transgenic sugar beet.

We have transformed sugar beet into a crop that produces fructans. The gene encoding 1-sucrose:sucrose fructosyl transferase (1-SST), which was isolated from Helianthus tuberosus, was introduced into sugar beet. In H. tuberosus, 1-SST mediates the first steps in fructan synthesis through the conversion of sucrose (GF) into low molecular weight fructans GF2, GF3, and GF4. In the taproot of sugar beet transformed with the 1-sst gene, the stored sucrose is almost totally converted into low molecular weight fructans. In contrast, 1-sst expression in the leaves resulted in only low levels of fructans. Despite the storage carbohydrate having been altered, the expression of the 1-sst gene did not have any visible effect on phenotype and did not affect the growth rate of the taproot as observed under greenhouse conditions.