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Oleaginous Green Alga Lobosphaera (Parietochloris) Incisa and Genetic Complementation of a Mutant Strain, Deficient in Arachidonic Acid Biosynthesis

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Oleaginous Green Alga Lobosphaera (Parietochloris) Incisa and Genetic Complementation of a Mutant Strain, Deficient in Arachidonic Acid Biosynthesis Development of a Nuclear Transformation System for Oleaginous Green Alga Lobosphaera (Parietochloris) incisa and Genetic Complementation of a Mutant Strain, Deficient in Arachidonic Acid Biosynthesis Boris Zorin1., Omer Grundman1., Inna Khozin-Goldberg1*, Stefan Leu1, Michal Shapira2, Yuval Kaye1, Nicolas Tourasse3, Olivier Vallon3, Sammy Boussiba1 1 Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel, 2 Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel, 3 UMR 7141 CNRS/Universite´ Pierre et Marie Curie, Institut de Biologie Physico-Chimique, Paris, France Abstract Microalgae are considered a promising source for various high value products, such as carotenoids, v-3 and v-6 polyunsaturated fatty acids (PUFA). The unicellular green alga Lobosphaera (Parietochloris) incisa is an outstanding candidate for the efficient phototrophic production of arachidonic acid (AA), an essential v-6 PUFA for infant brain development and a widely used ingredient in the baby formula industry. Although phototrophic production of such algal products has not yet been established, estimated costs are considered to be 2–5 times higher than competing heterotrophic production costs. This alga accumulates unprecedented amounts of AA within triacylglycerols and the molecular pathway of AA biosynthesis in L. incisa has been previously elucidated. Thus, progress in transformation and metabolic engineering of this high value alga could be exploited for increasing the efficient production of AA at competitive prices. We describe here the first successful transformation of L. incisa using the ble gene as a selection marker, under the control of the endogenous RBCS promoter. Furthermore, we have succeeded in the functional complementation of the L. incisa mutant strain P127, containing a mutated, inactive version of the delta-5 (D5) fatty acid desaturase gene. A copy of the functional D5 desaturase gene, linked to the ble selection marker, was transformed into the P127 mutant. The resulting transformants selected for zeocine resistant, had AA biosynthesis partially restored, indicating the functional complementation of the mutant strain with the wild-type gene. The results of this study present a platform for the successful genetic engineering of L. incisa and its long-chain PUFA metabolism. Citation: Zorin B, Grundman O, Khozin-Goldberg I, Leu S, Shapira M, et al. (2014) Development of a Nuclear Transformation System for Oleaginous Green Alga Lobosphaera (Parietochloris) incisa and Genetic Complementation of a Mutant Strain, Deficient in Arachidonic Acid Biosynthesis. PLoS ONE 9(8): e105223. doi:10. 1371/journal.pone.0105223 Editor: Marie-Joelle Virolle, University Paris South, France Received April 9, 2014; Accepted July 19, 2014; Published August 18, 2014 Copyright: ß 2014 Zorin et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. L. incisa strain used in this work is deposited at the Culture Collection of Algae at Go¨ttingen University under accession no. SAG 2468. Funding: This research was financially supported by the European Commission’s Seventh Framework Program for Research and Technology Development (FP7), project GIAVAP, Grant No. 266401. BZ, OG and YK acknowledge support from the Kreitman School of Advanced Graduate Studies at Ben-Gurion University. OV acknowledges support from the French state "Initiative d’Excellence" program (Grant "DYNAMO", ANR-11-LABX-0011-01). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors confirm that Prof. Michal Shapira is an Academic Editor for PLOS ONE. This does not alter their adherence to PLOS ONE Editorial policies and criteria. * Email: [email protected] . These authors contributed equally to this work. Introduction L. incisa is arachidonic acid (AA, 20:4 n-6). When cultivated under nitrogen starvation, the total FA content of the alga is over The green freshwater microalga Lobosphaera incisa (Reisigl) 35% of dry weight. AA constitutes about 60% of total FAs (TFA), comb. nov. was isolated from snow water patches in the alpine and over 90% of cell AA is deposited in TAGs, making L. incisa environment of Mt. Tateyama, Japan [1]. It belongs to the the richest plant source of the pharmaceutically and nutraceuti- Trebouxiophyceae, a class of Chlorophyte algae. Lobosphaera cally valuable AA and a target organism of high biotechnological incisa was initially assigned to the genus Parietochloris rather than interest [3] [4]. to Myrmecia [1] but was recently reclassified as belonging to The ability to store AA within reserve lipids, TAGs, was thought Lobosphaera based on zoospore morphology and 18S rDNA to be related to the need to maintain a buffering capacity for the analysis [2]. In contrast to most algae whose storage lipids long-chain polyunsaturated FA (LC-PUFA) pool under conditions triacylglycerols (TAGs) are mainly composed of saturated and of temperature change or growth recovery when rapid LC-PUFA monounsaturated fatty acids (FA), the main fatty acid in TAGs of incorporation into the cellular membranes is required for adjusting PLOS ONE | www.plosone.org 1 August 2014 | Volume 9 | Issue 8 | e105223 Nuclear Transformation System for Lobosphaera incisa membrane fluidity [5] [6]. The conversion of dihomo-c-linolenic isopropanol was added to the upper aqueous phase, and the DNA acid (DGLA, 20:3 n-6) to AA is mediated by the enzyme D5 was precipitated by centrifugation. The pellet was washed in 70% desaturase (DES5, GenBank: GU390533). Based on its chlorotic ethanol and resuspended in PCR grade water. The concentration phenotype at 15uC, we have been able to isolate P127, a L. incisa and purity of the DNA was determined by Nano-Drop (Thermo- mutant strain in DES5 [7] [8]. The chemically induced non-sense Scientific, Logan, UT). mutation caused a nucleotide alteration in the DES5 gene, leading to the appearance of stop codon and the complete loss of AA Isolation of RNA and cDNA synthesis biosynthesis. P127 accumulates DGLA, instead of AA, in TAGs The cells from 10 mL of culture with the chlorophyll content of and in polar lipids [8] [9]. 30 mg L-1 were harvested by centrifugation at 4000 rpm for In order to improve the biotechnological potential of L. incisa, 5 min, washed with double distilled sterilized water, flash-frozen in we developed a stable nuclear transformation system for its liquid N, and stored at 280uC until further use. Total RNA was metabolic engineering. Our initial attempts to transform this alga isolated following the SV Total RNA Isolation system protocol used the Streptomyces hindustanus ble gene as a selection marker (Promega, Madison, WI). cDNA was prepared from 1 mg of total connected to heterologous promoters, such as popular for RNA-template with the Verso cDNA kit (Thermo Fisher transformation of Chlamydomonas reinhardtii tandem HSP70A/ Scientific, Epson, UK). RBCS2 promoter [10], or the viral CaMV 35S. Using such constructs, transformation both by biolistic delivery and electro- Cloning procedures poration failed. Recent studies in microalgae engineering indicate PCR products were generated using the AccuPower PCR that the best transformation results are achieved by using cloned PreMix (Bioneer, Alameda, CA) and a TProfessional Thermo- endogenous promoters and regulatory untranslated regions cycler (Biometra, Goettingen, Germany). All PCR reactions were (UTRs), fused to suitable selection markers. In C. reinhardtii, made on standard conditions. The sequences of all primers used the PSAD, RBCS2 and HSP70A promoters have been widely are given in Table 1. PCR products were purified from agarose gel used to drive nuclear gene expression [11–13]. Other endogenous using the AccuPrep Gel Purification Kit (Bioneer). The In-Fusion promoters have been used to drive the expression of the ble gene, HD Cloning Kit (Clontech, Mountain View, CA) was used for the which encodes a protein that confers resistance to the antibiotic directional cloning of DNA fragments into target vectors, zeocin in many algal species. For example, the fcp promoter was according to the manufacturer’s instructions. successfully used for transformation of Phaeodactylum tricornutum [14] and likewise the bidirectional VCP2 promoter for transfor- mation of Nannochloropsis sp. [15]. Cloning of RBCS and DES5 genes Here we describe the development and characterization of a The RBCS gene, including 1 kb upstream of the predicted start transformation vector for the genetic engineering of L. incisa, codon and 430 bp downstream of the stop codon, was amplified based on the endogenous Ribulose-1,5-bisphosphate carboxylase/ using primers that annealed to the 59 (RbcS1kbF) and 39 (RbcSR) oxygenase (RuBisCO) small subunit (RBCS) promoter for ends of the gene sequence. The 6048 bp genomic loci of L. incisa expressing the ble gene as a selection marker. In order to containing DES5 gene, including 1.8 kb upstream of the predicted demonstrate the successful metabolic engineering of L. incisa,we start codon and 1 kb downstream of
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