Microalgae have received significant attention as potential next-generation microbiologic cell factories for biofuels. However, the production of microalgal biofuels is not yet sufficiently cost-effective for commercial applications. To screen higher lipid-producing strains, heavy carbon ion beams are applied to induce a genetic mutant. An RNA-seq technology is used to identify the pathways and genes of importance related to photosynthesis and biofuel production. The deep elucidation of photosynthesis and the fatty acid metabolism pathway involved in lipid yield is valuable information for further optimization studies. This study provided the photosynthetic efficiency and transcriptome profiling of a unicellular microalgae, Scenedesmus obliqnus mutant SO120G, with enhanced lipid production induced by heavy carbon ion beams. The lipid yield (52.5 mg L⁻¹) of SO120G mutant were enhanced 2.4 fold compared with that of the wild strain under the nitrogen deficient condition. In addition, the biomass and growth rate were 57% and 25% higher, respectively, in SO120G than in the wild type, likely owing to an improved maximum quantum efficiency (F_v/F_m) of photosynthesis. As for the major pigment compositions, the content of chlorophyll a and carotenoids was higher in SO120G than in the wild type. The transcriptome data confirmed that a total of 2077 genes with a change of at least twofold were recognized as differential expression genes (DEGs), of which 1060 genes were up-regulated and 1017 genes were down-regulated. Most of the DEGs involved in lipid biosynthesis were up-regulated with the mutant SO120G. The expression of the gene involved in the fatty acid biosynthesis and photosynthesis of SO120G was upregulated, while that related to starch metabolism decreased compared with that of the wild strain. This work demonstrated that heavy-ion irradiation is an promising strategy for quality improvement. In addition, the mutant SO120G was shown to be a potential algal strain for enhanced lipid production. Transcriptome sequencing and annotation of the mutant suggested the possible genes responsible for lipid biosynthesis and photosynthesis, and identified the putative target genes for future genetic manipulation and biotechnological applications.

Carbon-ion irradiation is a technique for trait improvement in the microalgae, but the underlying mechanisms that how it altered the biomass, and photosynthetic pigments accumulation were unclear. One mutant (DS240G-1) was obtained from Dunaliella salina by heavy ion irradiation mutagenesis. Compared to the wild type, the biomass accumulation and maximum growth rate of DS240G-1 were increased by 34% and 55% respectively, and its β-carotene content was 21% higher than the wild type. Subsequent analysis of the chlorophyll fluorescence parameters indicated that higher β-carotene productivity was likely owing to the improved maximum quantum efficiency (Fv/Fm) and decreased thermal dissipation of photosynthesis in DS240G-1 than that of wild type during cultivation. In addition, the result of this study revealed that high content of ROS may induce β-carotene accumulation in mutant DS240G-1. Also, the total fatty acid (TFA) content in mutant DS240G-1 was 79% higher than that in wild type. Owing to its high β-carotene productivity and total fatty acid content, DS240G-1 could be considered as a promising candidate for microalgae β-carotene and biodiesel production. This work provided the first insight into the biological effects involved in carbon-ions irradiation on the photosynthetic activity of D. salina. Keywords: microalgae, D. salina, carbon-ions irradiation, chlorophyll fluorescence, β-carotene DOI: 10.25165/j.ijabe.20211402.5993 Citation: Xi Y M, Liu Y, Chi Z Y, Yin L, Wang L J, Luo G H. Photosynthetic profiling of a Dunaliella salina mutant DS240G-1 with improved β-carotene productivity induced by heavy ions irradiation. Int J Agric & Biol Eng, 2021; 14(2): 211–217.

Drought adversely affects plant growth, which leads to reduced crop yields and exacerbates food insecurity. Late embryogenesis abundant (LEA) proteins are crucial for plants’ responses to abiotic stresses. This research further investigates the role of SiLEA5 by utilizing transgenic tomatoes under drought stress. The expression of SiLEA5 was upregulated under drought and abscisic acid (ABA) treatment, resulting in decreased electrolyte leakage and malondialdehyde content, alongside increased levels of osmotic regulators and antioxidant enzyme activity. These biochemical alterations reduce oxidative damage and enhance drought resistance. qRT-PCR analysis revealed the upregulation of ABA signaling genes and key enzymes involved in proline biosynthesis (P5CS) and dehydrin (DHN) synthesis under drought stress. Additionally, overexpression of SiLEA5 increased the net photosynthetic rate (Pn) and fruit yield of tomatoes by regulating stomatal density and aperture. These findings suggest that SiLEA5 may be a potential target for improving drought tolerance in tomatoes and other crops.