Two novel diacylglycerol acyltransferase genes from Xanthoceras sorbifolia are responsible for its seed oil content

Xanthoceras sorbifolia is an excellent model system for studying triacylglycerol (TAG) biosynthesis in woody oilseed plants due to the high amount of seed oil, which is important for food and industrial uses. TAG is the major form of stored lipids in seeds and diacylglycerol acyltransferase (DGAT; EC 2. 3. 1. 20) catalyzes the final and critical step of TAG synthesis. Here, two novel DGAT genes, designated XsDGAT1 and XsDGAT2, were cloned from developing X. sorbifolia embryos. Sequence analysis showed that XsDGAT1 had little sequence homology to XsDGAT2. Heterologous expression of XsDGAT1 and XsDGAT2 in TAG-deficient yeast mutants restored TAG synthesis, confirming their biological activity. Expression of the two genes in wild-type Arabidopsis led to TAG synthesis and an increase in total seed oil in transgenic plants, with XsDGAT1 appearing to contribute to TAG synthesis at a greater level. Comparison of the expression patterns revealed that both XsDGAT1 and XsDGAT2 were expressed in the examined tissues and had similar spatiotemporal expression patterns with higher expression in embryos than in leaves and petals. The expression patterns of both XsDGAT1 and XsDGAT2 correlated with oil accumulation in developing X. sorbifolia embryos. These data suggest that XsDGAT1 and XsDGAT2 are both responsible for TAG synthesis in X. sorbifolia seeds.     

Enhancement of phenol degradation by soil bioaugmentation with Pseudomonas sp. JS150

Aims: To test whether bioaugmentation with genetically modified Pseudomonas sp. JS150 strain could be used to enhance phenol degradation in contaminated soils. Methods and Results: The efficiency of phenol removal, content of humic carbon, survival of inoculant, number of total culturable autochthonous bacteria and changes in fatty acid methyl esters (FAME) profiling obtained directly from soils were examined. Bioaugmentation significantly accelerated phenol biodegradation rate in tested soils. Phenol applied at the highest concentration (5·0 mg g^?1 soil) was completely degraded in clay soil (FC) within 65 days, whereas in sand soil (FS) within 72 days. In comparison, phenol biodegradation proceeded for 68 and 96 days in nonbioaugmented FC and FS soils, respectively. The content of humic carbon remained at the same level at the beginning and the end of incubation time in all soil treatments. The number of introduced bacteria (2·50 × 10⁹ g^?1 soil) markedly decreased during the first 4 or 8 days depending on contamination level and type of soil; however, inoculant survived over the experimental period of time. Analysis of FAME patterns indicated that changes in the percentages of cyclopropane fatty acids 17:0 cy and 19:0 cyω10c and branched fatty acids might be useful markers for monitoring the progress of phenol removal from soil. Conclusions: It was confirmed that soil bioaugmentation with Pseudomonas sp. JS150 significantly enhanced soil activity towards phenol degradation. Cyclopropane and branched fatty acids were sensitive probes for degree of phenol utilization. Significance and Impact of the Study: In future, genetically modified Pseudomonas sp. JS150 strain could be of use in the bioaugmentation of phenol‐contaminated areas.     

Seed viability and fatty acid profiles of five orchid species before and after ageing

• Changes in seed lipid composition during ageing are associated with seed viability loss in many plant species. However, due to their small seed size, this has not been previously explored in orchids. We characterized and compared the seed viability and fatty acid profiles of five orchid species before and after ageing: one tropical epiphytic orchid from Indonesia (Dendrobium strebloceras), and four temperate species from New Zealand, D. cunninghamii (epiphytic), and Gastrodia cunninghamii, Pterostylis banksii and Thelymitra nervosa (terrestrial).
• Seeds were aged under controlled laboratory conditions (3-month storage at 60% RH and 20 °C). Seed viability was tested before and after ageing using tetrazolium chloride staining. Fatty acid methyl esters from fresh and aged seeds were extracted through trans-esterification, and then analysed using gas chromatography–mass spectrometry.
• All species had high initial viability (>80%) and experienced significant viability loss after ageing. The saturated, polyunsaturated, monounsaturated and total fatty acid content decreased with ageing in all species, but this reduction was only significant for D. strebloceras, D. cunninghamii and G. cunninghamii.
• Our results suggest that fatty acid degradation is a typical response to ageing in orchids, albeit with species variation in magnitude, but the link between fatty acid degradation and viability was not elucidated. Pterostylis banksii exemplified this variation; it showed marked viability loss despite not having a significant reduction in its fatty acid content after ageing. More research is required to identify the effect of ageing on fatty acid composition in orchids, and its contribution to seed viability loss.