Nannochloropsis, a rich source of diacylglycerol acyltransferases for engineering of triacylglycerol content in different hosts

Abstract

BackgroundPhotosynthetic microalgae are considered a viable and sustainable resource for biofuel feedstocks, because they can produce higher biomass per land area than plants and can be grown on non-arable land. Among many microalgae considered for biofuel production, Nannochloropsis oceanica (CCMP1779) is particularly promising, because following nutrient deprivation it produces very high amounts of triacylglycerols (TAG). The committed step in TAG synthesis is catalyzed by acyl-CoA:diacylglycerol acyltransferase (DGAT). Remarkably, a total of 13 putative DGAT-encoding genes have been previously identified in CCMP1779 but most have not yet been studied in detail.ResultsBased on their expression profile, six out of 12 type-2 DGAT-encoding genes (NoDGTT1-NoDGTT6) were chosen for their possible role in TAG biosynthesis and the respective cDNAs were expressed in a TAG synthesis-deficient mutant of yeast. Yeast expressing NoDGTT5 accumulated TAG to the highest level. Over-expression of NoDGTT5 in CCMP1779 grown in N-replete medium resulted in levels of TAG normally observed only after N deprivation. Reduced growth rates accompanied NoDGTT5 over-expression in CCMP1779. Constitutive expression of NoDGTT5 in Arabidopsis thaliana was accompanied by increased TAG content in seeds and leaves. A broad substrate specificity for NoDGTT5 was revealed, with preference for unsaturated acyl groups. Furthermore, NoDGTT5 was able to successfully rescue the Arabidopsis tag1-1 mutant by restoring the TAG content in seeds.ConclusionsTaken together, our results identified NoDGTT5 as the most promising gene for the engineering of TAG synthesis in multiple hosts among the 13 DGAT-encoding genes of N. oceanica CCMP1779. Consequently, this study demonstrates the potential of NoDGTT5 as a tool for enhancing the energy density in biomass by increasing TAG content in transgenic crops used for biofuel production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0686-8) contains supplementary material, which is available to authorized users.

Novel insights into salinity-induced lipogenesis and carotenogenesis in the oleaginous astaxanthin-producing alga Chromochloris zofingiensis: a multi-omics study

“…DGAT catalyzes the last committed step and has been demonstrated to play a critical role in TAG accumulation in various algal species [53,54,[60][61][62]. Recently, we showed by functional complementation in TAG-deficient yeast that seven out of the ten C. zofingiensis DGAT s were able to restore TAG synthesis, with DGAT1A being most functional followed by DGTT5 and DGAT1B [63].…”

Properties and Biotechnological Applications of Acyl‐CoA:diacylglycerol Acyltransferase and Phospholipid:diacylglycerol Acyltransferase from Terrestrial Plants and Microalgae

“…Following these aforementioned studies, many groups have further used DGAT1 from different species to boost seed content in various crops such as G. max (Hatanaka et al, ; Roesler et al, ), B. juncea (Savadi et al, ), Z. mays (Alameldin et al, ), C. sativa (Kim et al, ), and Jatropa curcas (Maravi et al, ). Moreover, overexpression of DGAT1 from microalgae, such as Chlorella ellipsoidea and Nannochloropsis oceanica , also led to increased oil content in Arabidopsis and B. napus (Guo et al, ; Zienkiewicz et al, ). Furthermore, DGAT1 has been used to increase the proportion of unusual fatty acids in seed oil, particularly epoxy fatty acid in G. max (coexpressed with an EPOXYGENASE gene; Li et al, ) and capric acid in C. sativa (in combination with fatty acyl‐ACP thioesterase B1 and LPAAT from Cuphea viscosissima ; Iskandarov et al, ).…”

Engineering microalgae through chloroplast transformation to produce high‐value industrial products

“…These algal species have also been genetically engineered to produce various biofuels. They are relatively easy to culture and large‐scale cultivation is conducted by various companies and institutes . Recently, Gan et al.…”