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

Abstract

Helianthus tuberosus L., known as the Jerusalem artichoke, is a hexaploid plant species, adapted to low-nutrient soils, that accumulates high levels of inulin in its tubers. Inulin is a fructose-based polysaccharide used either as dietary fiber or for the production of bioethanol. Key enzymes involved in inulin biosynthesis are well known. However, the gene networks underpinning tuber development and inulin accumulation in H. tuberous remain elusive. To fill this gap, we selected 6,365 expressed sequence tags (ESTs) from an H. tuberosus library to set up a microarray platform and record their expression across three tuber developmental stages, when rhizomes start enlarging (T 0), at maximum tuber elongation rate (T 3), and at tuber physiological maturity (T m), in "VR" and "K8-HS142"clones. The former was selected as an early tuberizing and the latter as a late-tuberizing clone. We quantified inulin and starch levels, and qRT-PCR confirmed the expression of critical genes accounting for inulin biosynthesis. The microarray analysis revealed that the differences in morphological and physiological traits between tubers of the two clones are genetically determined since T 0 and that is relatively low the number of differentially expressed ESTs across the stages shared between the clones (93). The expression of ESTs for sucrose:sucrose 1-fructosyltransferase (1-SST) and fructan: fructan 1-fructosyltransferase (1-FFT), the two critical genes for fructans polymerization, resulted to be temporarily synchronized and mirror the progress of inulin accumulation and stretching. The expression of ESTs for starch biosynthesis was insignificant throughout the developmental stages of the clones in line with the negligible level of starch into their mature tubers, where inulin was the dominant polysaccharide. Overall, our study disclosed candidate genes underpinning the development and storage of carbohydrates in the tubers of two H. tuberosus clones. A model according to which the steady-state levels of 1-SST and 1-FFT transcripts are developmentally controlled and might represent a limiting factor for inulin accumulation has been provided. Our finding may have significant repercussions for breeding clones with improved levels of inulin for food and chemical industry.

A Fructan Exohydrolase from Maize Degrades Both Inulin and Levan and Co-Exists with 1-Kestotriose in Maize

“…In general, fructan synthesis in plants requires the presence of fructosyltransferase enzymes. Most plants with FEH enzymes (including non-fructan plants) also have fructan synthesis and accumulation ability [ 12 , 20 , 30 , 36 , 37 ]. This work speculated maize may lack fructosyltransferases for fructan chain elongation.…”

Functional Characterization of MtrGSTF7, a Glutathione S-Transferase Essential for Anthocyanin Accumulation in Medicago truncatula

“…The PCR efficiency for each primer pair was tested as reported in [ 58 ]. Gene expression quantification was calculated using the (2 −ΔCt ) method as reported in [ 59 ] with actin as a reference gene. Three biological replicates were analysed, and the significance of the differences between mean expression values was analysed by t -test.…”

Light and Temperature Shape the Phenylpropanoid Profile of Azolla filiculoides Fronds

“…For each gene, four technical replicates were amplified. The efficiency of PCR for each primer pair was tested as reported in Escaray et al ( 2017 ) before the (2 −Δ Ct ) gene expression quantification method was applied based on the differences between the relative expression of the target genes and the reference EF-1a gene to compare the relative expression profiles among genes and treatments as reported in Bizzarri et al ( 2020 ). Four biological replicates for each treatment were analyzed; the significance of the expression values was analyzed by a two-way ANOVA ( p < 0.05) procedure embedded in the R statistical package.…”