Development of rubber‐enriched dandelion varieties by metabolic engineering of the inulin pathway

Abstract

SummaryNatural rubber (NR) is an important raw material for a large number of industrial products. The primary source of NR is the rubber tree Hevea brasiliensis, but increased worldwide demand means that alternative sustainable sources are urgently required. The Russian dandelion (Taraxacum koksaghyz Rodin) is such an alternative because large amounts of NR are produced in its root system. However, rubber biosynthesis must be improved to develop T. koksaghyz into a commercially feasible crop. In addition to NR, T. koksaghyz also produces large amounts of the reserve carbohydrate inulin, which is stored in parenchymal root cell vacuoles near the phloem, adjacent to apoplastically separated laticifers. In contrast to NR, which accumulates throughout the year even during dormancy, inulin is synthesized during the summer and is degraded from the autumn onwards when root tissues undergo a sink‐to‐source transition. We carried out a comprehensive analysis of inulin and NR metabolism in T. koksaghyz and its close relative T. brevicorniculatum and functionally characterized the key enzyme fructan 1‐exohydrolase (1‐FEH), which catalyses the degradation of inulin to fructose and sucrose. The constitutive overexpression of Tk1‐FEH almost doubled the rubber content in the roots of two dandelion species without any trade‐offs in terms of plant fitness. To our knowledge, this is the first study showing that energy supplied by the reserve carbohydrate inulin can be used to promote the synthesis of NR in dandelions, providing a basis for the breeding of rubber‐enriched varieties for industrial rubber production.

In vitro plant regeneration from ovules of Taraxacum officinale and Taraxacum koksaghyz

“…Insights into rubber biosynthesis in Taraxacum have been gained recently (metabolic engineering of inulin pathway), which may lay the basis for genetically engineered rubber-enriched plants (Stolze et al, 2017). The primary breeding objectives of Taraxacum are to increase the rubber content and the biomass yield of the roots.…”

Uncovering mechanisms of rubber biosynthesis in Taraxacum koksaghyz – role of cis‐prenyltransferase‐like 1 protein

“…In previous experiments, downregulating the rubber CPT subunits in T. brevicorniculatum resulted not only in depletion of rubber but also in enhancement of inulin and triterpenes (Post et al ., ). Additionally, inulin degradation has been found to positively influence rubber and triterpene levels (Stolze et al ., ). Both findings suggest that these metabolic pathways are closely related to rubber synthesis.…”

“…The Russian dandelion Taraxacum koksaghyz emerges as a potent alternative natural rubber (NR) source, because it synthesizes large amounts of high‐quality poly( cis ‐1,4‐isoprene) in its roots. In addition to rubber, T. koksaghyz produces other valuable compounds such as inulin, whose degradation influences NR productivity, as well as pentacyclic triterpenes, which modify the polymer's properties (Stolze et al ., ; Xu et al ., ). Inulin, the major storage carbohydrate in roots of dandelion species, is a β‐(2‐1)‐linked fructan (Van Laere and Van Den Ende, ), whereas pentacyclic triterpenes and NR represent functionally diverse isoprenoids.…”

Functional characterization of squalene synthase and squalene epoxidase in Taraxacum koksaghyz

“…Subsequently, the TkSQS1‐RNAi and the TkSQE1‐RNAi fragments were transferred to the pLab12.5‐pREF vector by LR recombination to generate pLab12.5‐pREF‐TkSQS1‐RNAi and pLab12.5‐pREF‐TkSQE1‐RNAi. The transformation of T. koksaghyz by A. tumefaciens strain EHA105 was carried out as previously described (Stolze et al., ). Oligonucleotide sequences are shown in Supporting Information Table .…”