Abstract
SummarySqualene is a linear intermediate to nearly all classes of triterpenes and sterols and is itself highly valued for its use in wide range of industrial applications. Another unique linear triterpene is botryococcene and its methylated derivatives generated by the alga Botryococcus braunii race B, which are progenitors to fossil fuel deposits. Production of these linear triterpenes was previously engineered into transgenic tobacco by introducing the key steps of triterpene metabolism into the particular subcellular compartments. In this study, the agronomic characteristics (height, biomass accumulation, leaf area), the photosynthetic capacity (photosynthesis rate, conductance, internal CO 2 levels) and triterpene content of select lines grown under field conditions were evaluated for three consecutive growing seasons. We observed that transgenic lines targeting enzymes to the chloroplasts accumulated 50–150 times more squalene than the lines targeting the enzymes to the cytoplasm, without compromising growth or photosynthesis. We also found that the transgenic lines directing botryococcene metabolism to the chloroplast accumulated 10‐ to 33‐fold greater levels than the lines where the same enzymes were targeted to in the cytoplasm. However, growth of these high botryococcene accumulators was highly compromised, yet their photosynthesis rates remained unaffected. In addition, in the transgenic lines targeting a triterpene methyltransferase (TMT) to the chloroplasts of high squalene accumulators, 55%–65% of total squalene was methylated, whereas in the lines expressing a TMT in the cytoplasm, only 6%–13% of squalene was methylated. The growth of these methylated triterpene‐accumulating lines was more compromised than that of nonmethylated squalene lines.
Highlights
Tobacco is an annually grown herbaceous plant that produces over 2500 compounds including terpenes, alkaloids, flavonoids and anthocyanins (Nugroho and Verpoorte, 2002)
Independent T0 transgenic lines expressing squalene synthase (SQS) with FPS targeted to the chloroplasts or the cytoplasm under the direction of constitutive (CaMV35S (Benfey and Chua, 1990) and CV35S cassava mosaic virus (Verdaguer et al, 1998)) or trichome-specific promoters (cbt1, cembratrien-ol synthase (Ennajdaoui et al, 2010) and CYP16 cytochrome P450 71D16 (Wang et al, 2002)) were generated by transforming each indicated construct into KY 1068 cultivars as described previously (Figure 2, Wu et al, 2012)
T1 lines constitutively expressing plastidic-targeted botryococcene synthase (SSL1-3(M)) with FPS, or homozygous T2 lines constitutively expressing plastidic-targeted SQS, were engineered with triterpene methyltransferase (TMT) targeted to the cytoplasm or the chloroplast, yielding lines with high levels of triterpene biosynthesis targeted to the plastid compartment with various combinations of methyltransferases targeted to either the plastid or cytoplasmic compartments (Figure 2; Jiang et al, 2016)
Summary
Tobacco is an annually grown herbaceous plant that produces over 2500 compounds including terpenes, alkaloids, flavonoids and anthocyanins (Nugroho and Verpoorte, 2002). It has been grown primarily for its use in smoke and smokeless consumer products that have abundant amounts of nicotine, nornicotine, anabasine and anatabine, thought important for its consumer preference (Siminszky et al, 2005). Tobacco has received much more attention recently because genetically enhanced tobacco has been suggested as an alternative platform for pharmaceuticals and biofuel production (Wu et al, 2012). When coupled with various genetic engineering approaches, transgenic lines can provide up to 6% of their dry weight as lipids and fatty acids suitable for biofuel and biodiesel uses, rivalling oil seed production capacities (Andrianov et al, 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
