Fatty Acid composition in tobacco I. Green tobacco plants

When the heat is on: High temperature resistance of buds from European tree species

The heat resistance of meristematic tissues is crucial for the survival of plants exposed to high temperatures, as experienced during a forest fire. Although the risk and frequency of forest fires are increasing due to climate change, knowledge about the heat susceptibility of buds, which enclose apical meristems and thus enable resprouting and apical growth, is scarce. In this study, the heat resistance of buds in two different phenological stages was experimentally assessed for 10 European tree species. Cellular heat tolerance of buds was analyzed by determining the electrolyte leakage following heat exposure. Further, the heat insulation capability was tested by measuring the time required to reach lethal internal temperatures linked to bud traits. Our results highlighted differences in cellular heat tolerance and insulation capability among the study species. The phenological stage was found to affect both the thermal stability of cells and the buds' insulation. Further, a good relationship between size-related bud traits and insulation capability was established. Species-specific data on the heat resistance of buds give a more accurate picture of the fire susceptibility of European tree species and provide useful information for estimating tree post-fire responses more precisely.

NtMYB12a acts downstream of sucrose to inhibit fatty acid accumulation by targeting lipoxygenase and SFAR genes in tobacco

MYB12 promotes flavonol biosynthesis in plants by targeting several early biosynthesis genes (EBGs) of this pathway. The transcriptions of these EBGs are also induced by sucrose signal. However, whether MYB12 is activated by sucrose signal and what the other roles MYB12 has in regulating plant metabolism are poorly understood. In this study, two NtMYB12 genes were cloned from Nicotiana tabacum. Both NtMYB12a and NtMYB12b are involved in regulating flavonoids biosynthesis in tobacco. NtMYB12a is further shown to inhibit the accumulation of fatty acid (FA) in tobacco leaves and seeds. Post-translational activation and chromatin immunoprecipitation assays demonstrate that NtMYB12a directly promotes the transcriptions of NtLOX6, NtLOX5, NtSFAR4 and NtGDSL2, which encode lipoxygenase (LOX) or SFAR enzymes catalyzing the degradation of FA. NtLOX6 and NtLOX5 are shown to prevent the accumulation of FA in the mature seeds and significantly reduced the percentage of polyunsaturated fatty acids (PUFAs) in tobacco. Sucrose stimulates the transcription of NtMYB12a, and loss function of NtMYB12a partially suppresses the decrease of FA content in tobacco seedlings caused by sucrose treatment. The regulation of sucrose on the expression of NtLOX6 and NtGDSL2 genes is mediated by NtMYB12a, whereas those of NtLOX5 and NtSFAR4 genes are independent of sucrose.

Design of high-oleic tobacco (Nicotiana tabacum L.) seed oil by CRISPR-Cas9-mediated knockout of NtFAD2-2

BACKGROUND

Tobacco seed oil could be used as an appropriate feedstock for biodiesel production. However, the high linoleic acid content of tobacco seed oil makes it susceptible to oxidation. Altering the fatty acid profile by increasing the content of oleic acid could improve the properties of biodiesel produced from tobacco seed oil.

RESULTS

Four FAD2 genes, NtFAD2-1a, NtFAD2-1b, NtFAD2-2a, and NtFAD2-2b, were identified in allotetraploid tobacco genome. Phylogenetic analysis of protein sequences showed that NtFAD2-1a and NtFAD2-2a originated from N. tomentosiformis, while NtFAD2-1b and NtFAD2-2b from N. sylvestris. Expression analysis revealed that NtFAD2-2a and NtFAD2-2b transcripts were more abundant in developing seeds than in other tissues, while NtFAD2-1a and NtFAD2-1b showed low transcript levels in developing seed. Phylogenic analysis showed that NtFAD2-2a and NtFAD2-2b were seed-type FAD2 genes. Heterologous expression in yeast cells demonstrated that both NtFAD2-2a and NtFAD2-2b protein could introduce a double bond at the Δ12 position of fatty acid chain. The fatty acid profile analysis of tobacco fad2-2 mutant seeds derived from CRISPR-Cas9 edited plants showed dramatic increase of oleic acid content from 11% to over 79%, whereas linoleic acid decreased from 72 to 7%. In addition, the fatty acid composition of leaf was not affected in fad2-2 mutant plants.

CONCLUSION

Our data showed that knockout of seed-type FAD2 genes in tobacco could significantly increase the oleic acid content in seed oil. This research suggests that CRISPR-Cas9 system offers a rapid and highly efficient method in the tobacco seed lipid engineering programs.

Effect of mcl-PHA synthesis in flax on plant mechanical properties and cell wall composition

The high demand for new biomaterials makes synthesis of polyhydroxyalkanoates (PHA) in plants an interesting and desirable achievement. Production of polymers in plants is an example of application of biotechnology for improving the properties of plants, e.g. industrial properties, but it can also provide knowledge about plant physiology and metabolism. The subject of the present study was an industrially important plant: flax, Linum usitatissimum L., of a fibre cultivar (cv Nike). In the study the gene encoding PHA synthase from Pseudomonas aeruginosa, fused to a peroxisomal targeting signal, was expressed in flax plants with the aim of modifying the mechanical properties of plants. Medium-chain-length (mcl) hydroxy acids in flax plants from tissue cultures were detected by GC-FID and FTIR method. The introduced changes did not affect fatty acid content and composition in generated flax plants. Since mcl-PHA are known as elastomers, the mechanical properties of created plants were examined. Modified plants showed increases in the values of all measured parameters (except strain at break evaluated for one modified line). The largest increase was noted for tensile stiffness, which was 2- to 3-fold higher than in wild-type plants. The values estimated for another parameter, Young's modulus, was almost at the same level in generated flax plants, and they were about 2.7-fold higher when compared to unmodified plants. The created plants also exhibited up to about 2.4-fold higher tensile strength. The observed changes were accompanied by alterations in the expression of selected genes, related to cell wall metabolism in line with the highest expression of phaC1 gene. Biochemical data were confirmed by spectroscopic methods, which also revealed that crystallinity index values of cellulose in modified flax plants were increased in comparison to wild-type flax plants and correlated with biomechanical properties of plants.

Identification of a secretory phospholipase A2 from Papaver somniferum L. that transforms membrane phospholipids

The full-length sequence of a new secretory phospholipase A2 was identified in opium poppy seedlings (Papaver somniferum L.). The cDNA of poppy phospholipase A2, denoted as pspla2, encodes a protein of 159 amino acids with a 31 amino acid long signal peptide at the N-terminus. PsPLA2 contains a PLA2 signature domain (PA2c), including the Ca(2+)-binding loop (YGKYCGxxxxGC) and the catalytic site motif (DACCxxHDxC) with the conserved catalytic histidine and the calcium-coordinating aspartate residues. The aspartate of the His/Asp dyad playing an important role in animal sPLA2 catalysis is substituted by a serine residue. Furthermore, the PsPLA2 sequence contains 12 conserved cysteine residues to form 6 structural disulfide bonds. The calculated molecular weight of the mature PsPLA2 is 14.0 kDa. Based on the primary structure PsPLA2 belongs to the XIB group of PLA2s. Untagged recombinant PsPLA2 obtained by expression in Escherichia coli, renaturation from inclusion bodies and purification by cation-exchange chromatography was characterized in vitro. The pH optimum for activity of PsPLA2 was found to be pH 7, when using mixed micelles of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and Triton X-100. PsPLA2 specifically cleaves fatty acids from the sn-2 position of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and shows a pronounced preference for PC over phosphatidyl ethanolamine, -glycerol and -inositol. The active recombinant enzyme was tested in vitro against natural phospholipids isolated from poppy plants and preferably released the unsaturated fatty acids, linoleic acid and linolenic acid, from the naturally occurring mixture of substrate lipids.

Metabolic Reconstruction of Setaria italica: A Systems Biology Approach for Integrating Tissue-Specific Omics and Pathway Analysis of Bioenergy Grasses

The urgent need for major gains in industrial crops productivity and in biofuel production from bioenergy grasses have reinforced attention on understanding C4 photosynthesis. Systems biology studies of C4 model plants may reveal important features of C4 metabolism. Here we chose foxtail millet (Setaria italica), as a C4 model plant and developed protocols to perform systems biology studies. As part of the systems approach, we have developed and used a genome-scale metabolic reconstruction in combination with the use of multi-omics technologies to gain more insights into the metabolism of S. italica. mRNA, protein, and metabolite abundances, were measured in mature and immature stem/leaf phytomers, and the multi-omics data were integrated into the metabolic reconstruction framework to capture key metabolic features in different developmental stages of the plant. RNA-Seq reads were mapped to the S. italica resulting for 83% coverage of the protein coding genes of S. italica. Besides revealing similarities and differences in central metabolism of mature and immature tissues, transcriptome analysis indicates significant gene expression of two malic enzyme isoforms (NADP- ME and NAD-ME). Although much greater expression levels of NADP-ME genes are observed and confirmed by the correspondent protein abundances in the samples, the expression of multiple genes combined to the significant abundance of metabolites that participates in C4 metabolism of NAD-ME and NADP-ME subtypes suggest that S. italica may use mixed decarboxylation modes of C4 photosynthetic pathways under different plant developmental stages. The overall analysis also indicates different levels of regulation in mature and immature tissues in carbon fixation, glycolysis, TCA cycle, amino acids, fatty acids, lignin, and cellulose syntheses. Altogether, the multi-omics analysis reveals different biological entities and their interrelation and regulation over plant development. With this study, we demonstrated that this systems approach is powerful enough to complement the functional metabolic annotation of bioenergy grasses.

Effects of DDT on the growth of crop plants

The effects of DDT on the germination and growth of plants were studied using many crop species. Of the species tested, oil-rich seeds of plants, such as peanut (Arachis hypogaea) and mustard (Brassica juncea), were more prone to DDT induced inhibition of germination and subsequent plant growth than cereals, pulses and fibre crops, like rice (Oryza sativa), barley (Hordeum vulgare), mung bean Vigna radiata), pigeon pea (Cajanus cajan) and cotton (Gossypium hirsutum). Studies with (14)C labelled DDT showed that insecticide uptake by seeds was directly proportional to seed size. However, there was no direct relationship between DDT uptake by the seeds and its subsequent translocation to the growing regions or the degree of growth inhibition. Data suggest that oil content of the seeds per se has a bearing on the susceptibility or tolerance of a plant to DDT. It is suggested that lipids of the plant cell solubilize and disperse DDT in the cytoplasm, which, in turn, affects normal metabolism within the cell.