Interaction between fructan metabolism and plant growth regulators.

MAIN CONCLUSION: The relationship of fructan to plant growth regulators is clearly more complicated than it looks and is likely related to differences between fructan molecules in size and structure as well as localization. Fructans are a complex group of carbohydrates composed mainly of fructose units linked to a sucrose molecule. Fructans are present in plants as heterogeneous mixtures with diverse molecular structures and mass, different polymerization degrees, and linkage types between fructosyl residues. Like sucrose, they are frequently stored in leaves and other organs, acting as carbohydrate reserves. Fructans are synthesized in the cell vacuole by fructosyltransferase enzymes and catabolized by fructan exohydrolase enzymes. Several publications have shown that fructan metabolism varies with the stage of plant development and in response to the environment. Recent studies have shown a correlation between plant growth regulators (PGR), fructan metabolism, and tolerance to drought and cold. PGR are compounds that profoundly influence the growth and differentiation of plant cells, tissues, and organs. They play a fundamental role in regulating plant responses to developmental and environmental signals. In this review, we summarize the most up-to-date knowledge on the metabolism of fructans and their crosstalk with PGR signaling pathways. We identify areas that require more research to complete our understanding of the role of fructans in plants.

Crystal Structure of a Sucrose-6-phosphate Hydrolase from Lactobacillus gasseri with Potential Applications in Fructan Production and the Food Industry.

Fructooligosaccharides (FOSs) are polymers of fructose with a prebiotic activity because of their production and fermentation by bacteria that inhabit the gastrointestinal tract and are widely used in the industry and new functional foods. Lactobacillus gasseri stands out as an important homofermentative microorganism related to FOS production, and its potential applications in the industry are undeniable. In this study, we report the production and characterization of a sucrose-6-phosphate hydrolase from L. gasseri belonging to the GH32 family. Apo-LgAs32 and LgAs32 complexed with ß-d-fructose structures were determined at a resolution of 1.94 and 1.84 Å, respectively. The production of FOS, fructans, 1-kestose, and nystose by the recombinant LgAs32, using sucrose as a substrate, shown in this study is very promising. When compared to its homologous enzyme from Lactobacillus reuteri, the production of 1-kestose by LgAs32 is increased; thus, LgAs32 can be considered as an alternative in fructan production and other industrial applications.

In Silico Analysis of the Structure of Fungal Fructooligosaccharides-Synthesizing Enzymes.

Fructooligosaccharides (FOS) are prebiotics commonly manufactured using fungal fructosyltransferases (FTases) or ß-fructofuranosidases. Several reports have attempted to optimize FOS production by changing operational conditions. Nevertheless, there is a lack of information related to the molecular enzyme-substrate interaction. In this study, we present an in silico evaluation of the interactions between substrates (i.e., glucose, sucrose, GF2, GF3, and GF4) and native FOS-synthesizing enzymes from fungi, with reported FOS production yield. In addition, a molecular dynamic simulation was conducted to assess the stability of these interactions. Six fungal enzymes with reported data of FOS production were selected: sucrose-sucrose 1-fructosyltransferase from A. foetidus (GenBank No. CAA04131); intracellular invertase from A. niger (GenBank No. ABB59679); extracellular invertase from A. niger (GenBank No. ABB59678); ß-fructofuranidase from A. japonicus ATCC 20611 (GenBank No. BAB67771); fructosyltransferase from A. oryzae N74 (GenBank No. ACZ48670); and fructosyltransferase from A. japonicus (PDB ID 3LF7). These enzymes shared an identity between 15 and 96 %, but have a highly conserved folding, and the characteristic FTases domains. Docking results showed that these enzymes also share a similar protein-ligand interaction profile. It was observed that the production yield of total FOS correlated with the sum of affinity energies for GF2, GF3, and GF4. Finally, we present the first molecular dynamic simulation for FOS and fungal FOS-synthesizing enzymes, showing that the protein-ligand interaction does not induce significant changes on the enzyme stability. Overall, these results represent valuable information to continue understanding the FOS synthesis process by fungal FOS-synthesizing enzymes, and they can have a significant impact toward the improvement in their catalytic properties and the synthesis of specific FOS.

Fructan active enzymes (FAZY) activities and biosynthesis of fructooligosaccharides in the vacuoles of Agave tequilana Weber Blue variety plants of different age.

MAIN CONCLUSION: Biosynthesis of agave fructans occurs in mesontle vacuoles which showed fluctuations in FAZY activities and synthesized a diverse spectrum of fructooligosaccharide isomers. Agave tequilana Weber Blue variety is an important agronomic crop in Mexico. Fructan metabolism in A. tequilana exhibits changes in fructan content, type, degree of polymerization (DP), and molecular structure. Specific activities of vacuolar fructan active enzymes (FAZY) in A. tequilana plants of different age and the biosynthesis of fructooligosaccharides (FOSs) were analyzed in this work. Vacuoles from mesontle (stem) protoplasts were isolated and collected from 2- to 7-year-old plants. For the first time, agave fructans were identified in the vacuolar content by HPAEC-PAD. Several FAZY activities (1-SST, 6-SFT, 6G-FFT, 1-FFT, and FEH) with fluctuations according to the plant age were found in protein vacuolar extracts. Among vacuolar FAZY, 1-SST activities appeared in all plant developmental stages, as well as 1-FFT and FEH activities. The enzymes 6G-FFT and 6-SST showed only minimal activities. Lowest and highest FAZY activities were found in 2- and 6-year-old plants, respectively. Synthesized products (FOS) were analyzed by TLC and HPAEC-PAD. Vacuolar FAZYs yielded large FOS isomers diversity, being 7-year-old plants the ones that synthesized a greater variety of fructans with different DP, linkages, and molecular structures. Based on the above, we are proposing a model for the FAZY activities constituting the FOS biosynthetic pathways in Agave tequilana Weber Blue variety.

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.

The expression of genes coding for sucrose:sucrose 1-fructosyltransferase (1-SST; EC 2.4.1.99) and fructan:fructan 1-fructosyltransferase (1-FFT; EC 2.4.1.100), both fructan biosynthesizing enzymes, characterization by TLC and HPAEC-PAD, as well as the quantification of the fructo-oligosaccharides (FOS) accumulating in response to the exogenous application of sucrose, kinetin (cytokinin) or other plant hormones associated with (a)biotic stress responses were determined in two Agave species grown in vitro, domesticated Agave tequilana var. azul and wild A. inaequidens. It was found that elicitors such as salicylic acid (SA), and jasmonic acid methyl ester (MeJA) had the strongest effect on fructo-oligosaccharide (FOS) accumulation. The exogenous application of 1mM SA induced a 36-fold accumulation of FOS of various degrees of polymerization (DP) in stems of A. tequilana. Other treatments, such as 50mM abscisic acid (ABA), 8% Sucrose (Suc), and 1.0 mg L(-1) kinetin (KIN) also led to a significant accumulation of low and high DP FOS in this species. Conversely, treatment with 200 µM MeJA, which was toxic to A. tequilana, induced an 85-fold accumulation of FOS in the stems of A. inaequidens. Significant FOS accumulation in this species also occurred in response to treatments with 1mM SA, 8% Suc, and 10% polyethylene glycol (PEG). Maximum yields of 13.6 and 8.9 mg FOS per g FW were obtained in stems of A. tequilana and A. inaequidens, respectively. FOS accumulation in the above treatments was tightly associated with increased expression levels of either the 1-FFT or the 1-SST gene in tissues of both Agave species.