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 (T0), at maximum tuber elongation rate (T3), and at tuber physiological maturity (Tm), 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 T0 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.

Highlights

  • Starch is the most common reserve carbohydrate in higher plants, about 15% of all flowering plant species store fructans

  • 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

  • New insights on gene expression and metabolism of storage carbohydrate accumulation in tubers of H. tuberosus stems from the present study, namely: i

Read more

Summary

Introduction

Starch is the most common reserve carbohydrate in higher plants, about 15% of all flowering plant species store fructans. These are linear and branched polymeric fructose extensions of sucrose (Suc) (Suzuki and Chatterton, 1993). The storage capacity of vacuoles may be larger than that of the plastids, accounting for up to 95% of the protoplast volume. The storage capacity of fructans is higher than that of starch (Brocklebank and Hendry, 1989), primarily when associated with the formation of specialized organs such as succulent stems, bulbs, and tubers

Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call