A high-oleic-acid and low-palmitic-acid soybean: agronomic performance and evaluation as a feedstock for biodiesel.

Phenotypic characterization of soybean event 335-13, which possesses oil with an increased oleic acid content (> 85%) and reduced palmitic acid content (< 5%), was conducted across multiple environments during 2004 and 2005. Under these conditions, the stability of the novel fatty acid profile of the oil was not influenced by environment. Importantly, the novel soybean event 335-13 was not compromised in yield in both irrigated and non-irrigated production schemes. Moreover, seed characteristics, including total oil and protein, as well as amino acid profile, were not altered as a result of the large shift in the fatty acid profile. The novel oil trait was inherited in a simple Mendelian fashion. The event 335-13 was also evaluated as a feedstock for biodiesel. Extruded oil from event 335-13 produced a biodiesel with improved cold flow and enhanced oxidative stability, two critical fuel parameters that can limit the utility of this renewable transportation fuel.

Co-expression of the borage Delta 6 desaturase and the Arabidopsis Delta 15 desaturase results in high accumulation of stearidonic acid in the seeds of transgenic soybean.

Two relatively rare fatty acids, gamma-linolenic acid (GLA) and stearidonic acid (STA), have attracted much interest due to their nutraceutical and pharmaceutical potential. STA, in particular, has been considered a valuable alternative source for omega-3 fatty acids due to its enhanced conversion efficiency in animals to eicosapentaenoic acid when compared with the more widely consumed omega-3 fatty acid, alpha-linolenic acid (ALA), present in most vegetable oils. Exploiting the wealth of information currently available on in planta oil biosynthesis and coupling this information with the tool of genetic engineering it is now feasible to deliberately perturb fatty acid pools to generate unique oils in commodity crops. In an attempt to maximize the STA content of soybean oil, a borage Delta(6) desaturase and an Arabidopsis Delta(15) desaturase were pyramided by either sexual crossing of transgenic events, re-transformation of a Delta(6) desaturase event with the Delta(15) desaturase or co-transformation of both desaturases. Expression of both desaturases in this study was under the control of the seed-specific soybean beta-conglycinin promoter. Soybean events that carried only the Delta(15 )desaturase possessed a significant elevation of ALA content, while events with both desaturases displayed a relative STA abundance greater than 29%, creating a soybean with omega-3 fatty acids representing over 60% of the fatty acid profile. Analyses of the membrane lipids in a subset of the transgenic events suggest that soybean seeds compensate for enhanced production of polyunsaturated fatty acids by increasing the relative content of palmitic acid in phosphatidylcholine and other phospholipids.

Ribozyme termination of RNA transcripts down-regulate seed fatty acid genes in transgenic soybean.

We investigated whether termination of transcripts with a self-cleaving ribozyme can enhance nuclear retention and serve as a tool to decrease specific plant gene expression. Nuclear retention was first monitored in tobacco using the beta-glucuronidase gene terminated with either the 35S CaMV 3' untranslated sequence (UTR) or a cis-acting ribozyme. Northern blot analysis of nuclear RNA and total RNA, and in situ hybridizations showed that the ribozyme-terminated transcripts were preferentially retained in the nucleus of transgenic tobacco. Ribozyme-terminated transcripts were subsequently tested as a gene down-regulation strategy in soybean. The embryo-specific Delta-12 fatty acid desaturase FAD2-1 gene was targeted because its down-regulation elevates oleic acid content of seed storage lipids. Both ribozyme-terminated antisense and standard antisense constructs were capable of gene down-regulation, producing over 57% oleic acid compared with less than 18% in wild-type seed. Ribozyme termination cassettes were also constructed to evaluate sense transcripts for single gene down-regulation and the simultaneous down-regulation of two embryo-specific genes in soybean using a single promoter. Eight independent soybean transformants were screened that harboured standard plus sense or ribozyme terminated FAD2-1 cassette. Two of the eight ribozyme terminated transformants displayed oleic acids levels in the seed storage lipids of over 75%, while none of the standard plus sense FAD2-1 lines showed elevated oleic acid phenotypes. The dual constructs targeted FAD2-1 and the FatB gene encoding a palmitoyl-thioesterase. Five transgenic soybean lines harbouring the dual constructs had oleic acid levels, greater than 85%, and saturated fatty acids levels, less than 6%. Thus, ribozyme termination of transcripts can be utilized to specifically down-regulate endogenous gene expression in soybean.