Cloning, Developmental, and Tissue-Specific Expression of Sucrose:Sucrose 1-Fructosyl Transferase from Taraxacum officinale. Fructan Localization in Roots

Abstract

Sucrose:sucrose 1-fructosyl transferase (1-SST) is the key enzyme initiating fructan synthesis in Asteraceae. Using reverse transcriptase-PCR, we isolated the cDNA for 1-SST from Taraxacum officinale. The cDNA-derived amino acid sequence showed very high homology to other Asteracean 1-SSTs (Cichorium intybus 86%, Cynara scolymus 82%, Helianthus tuberosus 80%), but homology to 1-SST from Allium cepa (46%) and Aspergillus foetidus (18%) was much lower. Fructan concentrations, 1-SST activities, 1-SST protein, and mRNA concentrations were compared in different organs during vegetative and generative development of T. officinale plants. Expression of 1-SST was abundant in young roots but very low in leaves. 1-SST was also expressed at the flowering stages in roots, stalks, and receptacles. A good correlation was found between northern and western blots showing transcriptional regulation of 1-SST. At the pre-flowering stage, 1-SST mRNA concentrations and 1-SST activities were higher in the root phloem than in the xylem, resulting in the higher fructan concentrations in the phloem. Fructan localization studies indicated that fructan is preferentially stored in phloem parenchyma cells in the vicinity of the secondary sieve tube elements. However, inulin-like crystals occasionally appeared in xylem vessels.

Development of rubber‐enriched dandelion varieties by metabolic engineering of the inulin pathway

“…From midsummer to autumn, the expression of the fructosyltransferases declined to nearly undetectable ( Tk1‐SST ) or low ( Tk1‐FFT ) levels in November, while the quantity and DP of inulin decreased. The correlation between fructosyltransferase expression and inulin levels has been already shown in chicory, Jerusalem artichoke and T. officinale (Koops and Jonker, 1996; Lüscher et al ., 1996; Van den Ende and Van Laere, 1996; Van den Ende et al ., 2000b). During the summer, an oversupply of photoassimilates seems to activate Tk1‐SST and Tk1‐FFT , promoting the accumulation of large amounts of high‐quality inulin in parenchymal cells adjacent to the root phloem (Javorsky, 1944; Van den Ende et al ., 2000b).…”

“…The correlation between fructosyltransferase expression and inulin levels has been already shown in chicory, Jerusalem artichoke and T. officinale (Koops and Jonker, 1996; Lüscher et al ., 1996; Van den Ende and Van Laere, 1996; Van den Ende et al ., 2000b). During the summer, an oversupply of photoassimilates seems to activate Tk1‐SST and Tk1‐FFT , promoting the accumulation of large amounts of high‐quality inulin in parenchymal cells adjacent to the root phloem (Javorsky, 1944; Van den Ende et al ., 2000b). The down‐regulation of fructosyltransferases from midsummer to autumn resulted in the accumulation of sucrose in the root cells of T. koksaghyz (Figure 2b).…”

“…Fructans are water‐soluble reserve carbohydrates that are thought to be synthesized and stored within the vacuoles in ~15% of all angiosperm species, including chicory ( Cichorium intybus ), Jerusalem artichoke ( Helianthus tuberosus ), artichoke ( Cynara scolymus ) and dandelions, and several cereals and grasses (Carpita et al ., 1991; Darwen and John, 1989; Hellwege et al ., 2000; Hendry, 1987; Van den Ende et al ., 2000b; Wagner et al ., 1983). Dandelion inulin crystals are clustered in parenchymal root cell vacuoles close to phloem tissues adjacent to laticifers (Javorsky, 1944; Van den Ende et al ., 2000b) (Figure 1).…”

“…Fructans are water‐soluble reserve carbohydrates that are thought to be synthesized and stored within the vacuoles in ~15% of all angiosperm species, including chicory ( Cichorium intybus ), Jerusalem artichoke ( Helianthus tuberosus ), artichoke ( Cynara scolymus ) and dandelions, and several cereals and grasses (Carpita et al ., 1991; Darwen and John, 1989; Hellwege et al ., 2000; Hendry, 1987; Van den Ende et al ., 2000b; Wagner et al ., 1983). Dandelion inulin crystals are clustered in parenchymal root cell vacuoles close to phloem tissues adjacent to laticifers (Javorsky, 1944; Van den Ende et al ., 2000b) (Figure 1). The abundance of photoassimilates during the summer leads to the continuous accumulation of inulin during vegetative growth, as shown in chicory, Jerusalem artichoke and dandelions (van Arkel et al ., 2012; Javorsky, 1944; Marx et al ., 1997; Schorr‐Galindo and Guiraud, 1997; Van den Ende et al ., 2000b).…”

Cloning and Functional Analysis of Sucrose:Sucrose 1-Fructosyltransferase from Tall Fescue

“…As originally postulated by Edelman and Jefford (1968), inulin is synthesized from Suc via a trisaccharide intermediate by the concerted action of two distinct fructosyltransferases: (a) Suc:Suc 1-fructosyltransferase (1-SST, EC 2.4.1.99), which produces the inulin trisaccharide 1-kestose (isokestose) and Glc from Suc (Koops and Jonker, 1996;Lü scher et al, 1996;Lü scher et al, 2000; Van den Ende et al, 2000), and (b) fructan: fructan 1-fructosyltransferase (1-FFT, EC 2.4.1.100; Lü scher et al, 1993;Koops and Jonker, 1994), which transfers Fru moieties between fructan molecules.…”