Draft genome sequence and genetic transformation of the oleaginous alga Nannochloropsis gaditana

Abstract

The potential use of algae in biofuels applications is receiving significant attention. However, none of the current algal model species are competitive production strains. Here we present a draft genome sequence and a genetic transformation method for the marine microalga Nannochloropsis gaditana CCMP526. We show that N. gaditana has highly favourable lipid yields, and is a promising production organism. The genome assembly includes nuclear (~29 Mb) and organellar genomes, and contains 9,052 gene models. We define the genes required for glycerolipid biogenesis and detail the differential regulation of genes during nitrogen-limited lipid biosynthesis. Phylogenomic analysis identifies genetic attributes of this organism, including unique stramenopile photosynthesis genes and gene expansions that may explain the distinguishing photoautotrophic phenotypes observed. The availability of a genome sequence and transformation methods will facilitate investigations into N. gaditana lipid biosynthesis and permit genetic engineering strategies to further improve this naturally productive alga.

RNA-Seq and metabolic flux analysis of Tetraselmis sp. M8 during nitrogen starvation reveals a two-stage lipid accumulation mechanism

“…M8, although FA synthesis was down-regulated, the down-regulation of genes (TAG lipase, ACSase) at the committing steps, as well as at the ECH-gene of the β-oxidation pathway may indicate that the observed increase in lipid accumulation at this time point is a result of reduced lipid degradation, rather than increased lipid synthesis. This observation has also been observed in Nannochloropsis gaditana, where the lack of up-regulation amongst lipid biosynthesis genes despite increased lipid production has been attributed to sufficiently abundant existing lipid production machinery carried over from growth phase, coupled with a shift in carbon flux away from carbohydrate synthesis (Radakovits et al, 2012). There is evidence supporting this in Tetraselmis sp.…”

Methylcrotonyl-CoA Carboxylase Regulates Triacylglycerol Accumulation in the Model Diatom Phaeodactylum tricornutum

“…Although it was postulated that catabolism of amino acids in microalgae under nitrogen starvation would yield various TCA intermediates that could feed into the TCA cycle and be directed to fatty acid biosynthesis (Hockin et al, 2012;Radakovits et al, 2012), our findings provide compelling evidence that it is principally BCAA catabolism that contributes to TAG biosynthesis in this way. Responses of genes encoding lipid biosynthetic enzymes during TAG accumulation in P. tricornutum were almost the same as those in plants and C. reinhardtii (Miller et al, 2010;Chapman and Ohlrogge, 2012), but different from those in oleaginous Nannochloropsis species (Radakovits et al, 2012;Vieler et al, 2012). Nannochloropsis species constitutively produce TAG even during logarithmic growth, and few genes that are directly involved in lipid biosynthesis are transcriptionally upregulated to a significant extent.…”

Choreography of Transcriptomes and Lipidomes ofNannochloropsisReveals the Mechanisms of Oil Synthesis in Microalgae

“…Because carbon fixation efficiency can be affected by intracellular CO 2 concentrations, we examined the transcriptional dynamics of a number of genes involved in CO 2 concentration regulation mechanisms. Both carbonic anhydrase (CA)-mediated carbon-concentrating metabolism and a C4 cyclelike mechanism have previously been reported in heterokonts, including several diatoms and Nannochloropsis spp (Roberts et al, 2007;Kroth et al, 2008;Radakovits et al, 2012;Vieler et al, 2012). In IMET1, five putative CA genes were identified, along with two putative bicarbonate transporters and two low CO 2 -inducible genes (LCIA) that encode a putative formate/nitrite transporter protein in the plastid envelope.…”

“…In C. reinhardtii, the excess photosynthetically fixed carbons and energy are mainly stored in the form of starch and to a much lesser extent TAG under high light or under high light plus N depletion (Buléon et al, 1997;Li et al, 2010aLi et al, , 2010b. In oleaginous microalgae (e.g., Nannochloropsis spp), TAG is the main carbon and energy reserve along with smaller amounts of the water-soluble polysaccharide chrysolaminarin under stress conditions (Radakovits et al, 2012;Vieler et al, 2012;Wang et al, 2014). The genetic makeup and molecular mechanisms that bestow oleaginous microalgae the ability to produce extraordinary amounts of TAG in response to stress remain to be elucidated.…”

“…Nannochloropsis species/strains are of industrial interest due to their ability to grow rapidly, synthesize large amounts of TAGs and high-value polyunsaturated FAs (e.g., eicosapentaenoic acid), and tolerate broad environmental and culture conditions (Sukenik, 1991;Wang et al, 2012). Recently, the genomes of multiple species of Nannochloropsis have been sequenced and partially annotated (Radakovits et al, 2012;Vieler et al, 2012;Wei et al, 2013;Wang et al, 2014). Several transcriptomic analyses have also been conducted with Nannochloropsis (Vieler et al, 2012;Carpinelli et al, 2013;Zheng et al, 2013); however, the individual-snapshot mRNA analyses, which tested only one or two time points, has failed to capture the temporal dynamics of gene expression.…”