Developmental modulation of inulin accumulation in storage organs of transgenic maize and transgenic potato

Many important health promoting and functional characteristics are attributed to the non-digestible polysaccharide, inulin. Its use as a prebiotic in functional food and feed has further increased inulin demand worldwide. Inulin production in crops used for food and feed application, such as maize and potato, may provide a more direct and cost-effective route to provide functional food or feed when compared to native inulin producers. Towards this end we have expressed the inulin synthesizing enzymes, 1-SST and 1-FFT from Jerusalem artichoke in maize and potato. Transgenic maize plants produced inulin type fructan (at 3.2 mg/g kernel) when expressing an endosperm targeted gene cassette. Kernel development and germination were not affected. Potato tubers expressing 1-sst accumulated 1.8 mg inulin/g tuber while tubers with a combined expression of 1-sst and 1-fft accumulated 2.6 mg inulin/g tuber. Inulin accumulation in maize kernels was modulated by kernel development. Inulin levels peaked and then underwent moderate degradation by late kernel development. In potato, inulin production was relatively stable throughout tuber development and little evidence of degradation was observed. The accumulation of 1-kestose in transgenic maize was positively correlated with kernel sucrose concentration. Introduction of the fructan synthetic pathway in a high-sucrose maize background increased inulin accumulation to 41 mg/g kernel. Evidence is presented indicating that sucrose availability is limiting fructan production in transgenic maize.