Dissecting the regulation of fructan metabolism in chicory (Cichorium intybus) hairy roots

Abstract

Summary• Fifteen per cent of higher plants accumulate fructans. Plant development, nutritional status and stress exposure all affect fructan metabolism, and while fructan biochemistry is well understood, knowledge of its regulation has remained fragmentary. Here, we have explored chicory (Cichorium intybus) hairy root cultures (HRCs) to study the regulation of fructan metabolism in sink tissues in response to environmental cues.• In standard medium (SM), HRCs did not accumulate inulin. However, upon transfer to high-carbon (C)/low-nitrogen (N) medium, expression of sucrose:sucrose 1-fructosyltransferase (1-SST) and fructan:fructan 1-fructosyltransferase (1-FFT) was strongly induced and inulin accumulated. Upon return to SM, inulin was degraded, together with a coordinate decline of 1-SST and 1-FFT expression. In HRCs, coldinduced expression of fructan 1-exohydrolases (1-FEH I and IIa) was similar to cold induction in taproots, even in the absence of accumulated inulin.• For high-C/low-N induction of 1-SST and 1-FFT, and cold induction of 1-FEH I and IIa, the signaling pathways were addressed. While 1-SST and 1-FFT induction was similarly prevented by inhibitors of Ca 2+ signaling, protein kinases and phosphatases, cold induction of 1-FEH I and IIa revealed distinct signaling pathways.• In summary, this study has established chicory HRCs as a convenient experimental system with which to study the regulation of fructan active enzyme (FAZY) expression in heterotrophic cells.

Linking Expression of Fructan Active Enzymes, Cell Wall Invertases and Sucrose Transporters with Fructan Profiles in Growing Taproot of Chicory (Cichorium intybus): Impact of Hormonal and Environmental Cues

“…In a study on chicory hairy roots, it was shown that for their induction 1-FEH1 and 1-FEH2 require different signaling pathways (Kusch et al, 2009), this notion being corroborated by the observation that in a time-course study ABA induction of 1-FEH1 preceded 1-FEH2 induction (Bausewein, 2014; see also Figure 4 ). When comparing the induction kinetics of VI after cold-treatment ( Figure 8 ) and ABA-treatment ( Figure 4 ), the increased expression is strong but transient in both cases, leading to comparable increases of glucose of young taproots ( Figures 5 and 9 ).…”

“…A similar effect of sucrose on fructan synthesis has been shown in other fructan-accumulating plant species (Maleux and Van den Ende, 2007; Xue et al, 2011). However, a higher C/N-ratio, rather than high sucrose alone, was shown to be the major determinant for 1-SST and 1-FFT induction in chicory hairy root cultures (Kusch et al, 2009). …”

“…Measurements were operated on a Dionex ICS-3000 system with the Chromeleon 6.60 software (all components from Dionex). The extraction of total soluble carbohydrates was described in detail by Kusch et al (2009). In brief, aliquots of the final supernatant were dried in a speedvac concentrator (Bachofer, Reutlingen, Germany).…”

“…Source-to-sink transport of sucrose can be affected by many environmental factors, such as water and salt stress, N- and P-deficiency and temperature (Lemoine et al, 2013), these factors also exerting a profound impact on hormonal signaling. For chicory, the expression of FAZY genes in response to several environmental cues including N-deficiency (Kusch et al, 2009) and various abiotic stresses has been the subject of previous studies (De Roover et al, 2000; Michiels et al, 2004; Valluru and Van den Ende, 2008). Conversely, studies linking expression of genes involved in sucrose allocation from source to sink with expression profiles for FAZY genes have not yet been reported.…”

Expression of the 1-SST and 1-FFT genes and consequent fructan accumulation in Agave tequilana and A. inaequidens is differentially induced by diverse (a)biotic-stress related elicitors

“…Fructans are water soluble reserve carbohydrates found in several angiosperms adapted to regions having seasonal cold and dry periods (Vijn and Smeekens, 1999). Due to their water solubility and resistance to crystallization at freezing temperatures, they undergo biosynthesis at low temperatures, stabilize phospholipid membranes, adjust the osmotic pressure by hexose sugars release Kusch et al, 2009) and act as scavengers of reactive oxygen species (ROS) in the vicinity of vacuolar membranes (Peshev et al, 2013). They are believed to contribute to the protection against abiotic stress caused by cold (Pollock et al, 1988;Hisano et al, 2008), excessive salinity (Kerepesi and Galiba, 2000), drought Livingston et al, 2009) and/or oxidative stress (Peshev et al, 2013).…”