Characterization of Fructan Metabolism During Jerusalem Artichoke (Helianthus tuberosus L.) Germination

Abstract

The inulin-type fructans in Jerusalem artichoke (Helianthus tuberosus L.) tubers exhibit different degrees of polymerization and are critical for germination. We aimed to characterize the sugar metabolism dynamics in the tubers without bud eyes or shoots (T) and BE/S of indoor- and field-grown Jerusalem artichokes during germination. Ht1-FEH II and Ht1-FEH III (1-fructan exohydrolases II and III, inulin-degrading enzymes) expression increased 5 days after planting indoors, whereas Ht1-FEH II expression increased 72 days after planting in the field in T and BE/S. Ht1-SST (sucrose:sucrose 1-fructosyl transferase, inulin synthesis initiator), and Ht1-FFT (fructan:fructan 1-fructosyl transferase, inulin elongator) expression generally decreased in indoor-grown T. The enzyme activities of 1-FEH and 1-FFT were unchanged during germination in both indoor- and field-grown T and BE/S, whereas 1-SST activity decreased in indoor-grown T, while 1-FEH and 1-FFT activities increased as a function of germination time in BE/S of both indoor- and field-grown tubers. The total soluble sugar content gradually decreased in T after germination indoors or in the field, while at the end of germination, the sucrose and fructan contents decreased, and fructose content increased in the field. The enzyme activities of soluble vacuolar (VI) or neutral invertase (NI) did not change significantly, except at the late germination stage. Sucrose synthase (SS) and sucrose-phosphate synthase (SPS) activities were not significantly changed in T and BE/S in indoor-grown artichokes, while SS activity gradually increased, and SPS activity gradually decreased in field-grown artichokes, alongside sucrose degradation. Compared to T, BE/S generally had higher enzyme activities of 1-FEH and 1-FFT, promoting inulin hydrolysis. This work shows that the process of tuber germination is similar indoors and in the field, and germination studies can therefore be conducted in either environment.

A 6&1-FEH Encodes an Enzyme for Fructan Degradation and Interact with Invertase Inhibitor Protein in Maize (Zea mays L.)

“…Fructan biosynthetic enzymes (FBEs, e.g., sucrose:sucrose 1-fructosyltransferase, fructan:fructan 1-fructosyltransferase, sucrose:fructan 6-fructosyltransferase) are evolutionarily related to acid invertases present in all higher plants, but catalyze, depending on the plant species, the synthesis of different types of fructans, differing in the linkage between fructose units (i.e., 6→2 (levan type), 1→2 (inulin type), or branched) [2]. Fructan degradation is catalyzed by fructan exohydrolases (FEHs), which remove terminal fructose units [3,4,5]. FEH enzymes may either be specific for α-(2,1) fructose linkages (1-FEHs: Inulinases), for α-(2,6) fructose linkages (6-FEHs, levanases), or may hydrolyze both types of fructans (6&1-FEHs).…”

Whole-Transcriptome Analysis Unveils the Synchronized Activities of Genes for Fructans in Developing Tubers of the Jerusalem Artichoke

“…A recent study has characterized the transcriptional levels of 1-SST and 1-FFT genes and measured the activity of the enzymes coded by these genes and by fructan exohydrolase (FEHs) genes, essential for inulin degradation, to analyze the sugar metabolism dynamics in tubers and bud eyes/shoots of a cultivar of H. tuberosus during germination (Jiao et al, 2018). The transcriptional profiles of the Jerusalem artichoke FEHs under stress was also investigated (Xu et al, 2015).…”

“…However, despite the wealth of knowledge on the enzymology of inulin in H. tuberosus, the gene networks underpinning tuber development and inulin accumulation therein have yet to be fully elucidated. There are only few studies aimed at unearthing the transcriptional profiles of genes involved in carbohydrate accumulation and metabolism in these organs (Jung et al, 2014;Jiao et al, 2018).…”

Exohidrolasas fructosílicas y su importancia en el metabolismo de fructanos en Agave tequilana Weber var. azul

“…Sumado a los intentos realizados para mejorar la concentración y el DP de fructanos en las plantas de agave mediante la optimización de las condiciones de cultivo, existe un interés creciente en la aplicación de estrategias desarrolladas por la ingeniería genética. Por otro lado, se han realizado avances en el conocimiento de las vías metabólicas de síntesis de fructanos en las plantas a partir del estudio de determinadas enzimas, como las hidrolasas glicosídicas [8,71].…”

“…La hidrólisis de estos carbohidratos se realiza con exohidrolasas fructosílicas (FEH), las cuales son enzimas que retiran los residuos de fructosa terminales [7,8]. El estudio de estas enzimas en la planta Agave tequilana Weber var.…”