The Arabidopsis (Arabidopsis thaliana) acyl-coenzyme A (CoA) desaturase-like (ADS) gene family contains nine genes encoding fatty acid desaturase-like proteins. The biological function of only one member of the family, fatty acid desaturase5 (AtADS3/ FAD5, At3g15850), is known, and this gene encodes the plastidic palmitoyl-monogalactosyldiacylglycerol D7 desaturase. We cloned seven members of the gene family that are predicted not to have a chloroplast transit peptide and expressed them in the yeast Saccharomyces cerevisiae. All seven have previously undescribed desaturase activity on very-long-chain fatty acid (VLCFA) substrates and exhibit diverse regiospecificity, catalyzing introduction of double bonds relative to the methyl end of the molecule (n-x) at n-6 (AtADS4, At1g06350), n-7 (AtADS1.3, At1g06100 and AtADS4.2, At1g06360), n-9 (AtADS1, At1g06080 and AtADS2, At2g31360) or D9 (relative to the carboxyl end of the molecule) positions (AtADS1.2, At1g06090 and AtADS1.4, At1g06120). Through forward and reverse genetics it was shown that AtADS2 is involved in the synthesis of the 24:1(n-9) and 26:1(n-9) components (X:Y, where X is chain length and Y is number of double bonds) of seed lipids, sphingolipids, and the membrane phospholipids phosphatidylserine, and phosphatidylethanolamine. Plants deficient in AtADS2 expression showed no obvious phenotype when grown under normal growing conditions, but showed an almost complete loss of phosphatidylethanolamine (42:4), phosphatidylserine(42:4), dihydroxy-monohexosylceramide(42:2)-2, trihydroxy-monohexosylceramide(42:2)-3, and trihydroxy-glycosylinositolphosphoceramide(42:2)-3, lipid species that contain the VLCFA 24:1(n-9), and trihydroxyglycosylinositolphosphoceramide(44:2)-3, a lipid containing 26:1(n-9). Acyl-CoA profiling of these plants revealed a major reduction in 24:1-CoA and a small reduction in 26:1-CoA. Overexpression of AtADS2 resulted in a substantial increase in the percentage of glycerolipid and sphingolipids species containing 24:1 and a dramatic increase in the percentage of very-long-chain monounsaturated fatty acids in the acyl-CoA pool. Plants deficient in AtADS1 expression had reduced levels of 26:1(n-9) in seed lipids, but no significant changes in leaf phospholipids or sphingolipids were observed. These findings indicate that the 24-carbon and 26-carbon monounsaturated VLCFAs of Arabidopsis result primarily from VLCFA desaturation, rather than by elongation of long chain monounsaturated fatty acids.

Fusarium head blight (FHB) is a serious disease of wheat worldwide. Cultivar resistance to FHB depends on biochemical factors that confine the pathogen spread in spikes. Breeding for cultivar resistance is considered the most practical way to manage this disease. In this study, different spectroscopy and microscopy techniques were applied to discriminate resistance in wheat genotypes against FHB. Synchrotron-based spectroscopy and imaging techniques, including focal plane array infrared and X-ray fluorescence (XRF) spectroscopy were used to understand changes in biochemical and nutrients in rachis following FHB infection. Sumai3 and Muchmore were used to represent resistant and susceptible cultivars to FHB, respectively, in this study. The histological comparison of rachis showed substantial differences in the cell wall thickness between the cultivars after infection. Synchrotron-based infrared imaging emphasized substantial difference in biochemical composition of rachis samples between the two cultivars prior to visible symptoms; in the resistant Sumai3, infrared bands representing lignin and hemicellulose were stronger and more persistent compared to the susceptible cultivar. These bands may be the candidates of biochemical markers for FHB resistance. Focal plane array infrared imaging (FPA) spectra from the rachis epidermis and vascular bundles revealed a new band (1710 cm−1) related to the oxidative stress on the susceptible cultivar only. XRF spectroscopy data revealed differences in nutrients composition between cultivars, and between controls and inoculated samples, with substantial increases observed for Ca, K, Mn, Fe, Zn, and Si in the resistant cultivar. These nutrients are related to cell wall stability, metabolic process, and plant defense mechanisms such as lignification pathway and callose deposition. The combination of cell wall composition and lignification plays a role in the mechanism of type II host resistance to FHB. Biochemical profiling using the synchrotron-based spectroscopy holds potential for screening wheat genotypes for FHB resistance.

SummaryNo temperate oilseeds crops are available that produce oil with a high saturated fatty acid content. To achieve such a profile, Brassica napus cv. DH12075 was engineered by simultaneous seed-specific over-expression of a native fatty acyl-ACP thioesterase B [BnFatB(2)] and artificial microRNA-mediated down-regulation of eight endogenous genes encoding putative stearoyl-ACP desaturases (BnSADs). Semi-quantitative RT-PCR analysis of transformed lines showed that the BnFatB(2) gene was highly over-expressed and the eight putative SAD genes were strongly down-regulated in developing seed demonstrating the successful application of microRNA as a tool for down-regulation of genes in the allotetraploid plant B. napus. Analysis of seed triacylglycerol (TAG) composition revealed that all lines contained high levels of palmitic acid (16:0) and moderately increased levels of stearic acid (18:0). Total saturated fatty acid content was increased from 7.4% in the control to 37.3-45.6% in the transformed lines, with FatB overexpression as the dominant trait. A twofold increase in 16:0 was observed in seed polar lipids. The melting point of oil from mature seeds was increased from À10°C in DH12075 to 15°C in the line with the highest saturated fatty acid content. TAG composition showed a shift from predominantly C54 TAG to C50 and C52 TAGs enriched in palmitic acid. Seedling establishment at low temperature was compromised in lines with high saturated fatty acid content. Results suggested that transcript encoding stearoyl-ACP desaturase in developing B. napus seeds is present in considerable excess of the level required for efficient desaturation of 18:0.