Inulin metabolism in dicots: chicory as a model system

Fructans are fructose-based oligo- and polymers that serve as reserve carbohydrates in many plant species. The original Edelman and Jefford model for GF(n) inulin type fructan biosynthesis was confirmed by the de novo synthesis of fructans in vitro as well as by heterologous expression of the respective cDNAs in non-fructan plants. Now the model can be extended for the biosynthesis of F(n) inulin type fructans. Recent progress has now succeeded in elucidating the biochemistry and molecular biology of fructan biodegradation in chicory, an economically important species used for commercial inulin extraction. Unlike fructan biosynthetic genes that originated from vacuolar type invertase, plant fructan exohydrolases seem to have evolved from a cell wall invertase ancestor gene that later obtained a low iso-electric point and a vacuolar targeting signal. Using chicory as a model system, expression analysis revealed that fructan enzymes are mainly controlled at the transcriptional level.