The negative association between protein and oil production in soybean (Glycine max) seed is well-documented. However, this inverse relationship is based primarily on the composition of mature seed, which reflects the cumulative result of events over the course of soybean seed development and therefore does not convey information specific to metabolic fluctuations during developmental growth regimes. In this study, we assessed maternal nutrient supply via measurement of seed coat exudates and metabolite levels within the cotyledon throughout development to identify trends in the accumulation of central carbon and nitrogen metabolic intermediates. Active metabolic activity during late seed development was probed through transient labeling with 13C substrates. The results indicated: i) a drop in lipid contents during seed maturation with a concomitant increase in carbohydrates, ii) a transition from seed filling to maturation phases characterized by quantitatively balanced changes in carbon use and CO2 release, iii) changes in measured carbon and nitrogen resources supplied maternally throughout development, iv) 13C metabolite production through gluconeogenic stepsfor sustained carbohydrate accumulation as the maternal nutrient supply diminishes, and v) oligosaccharide biosynthesis within the seed coat during the maturation phase. These results highlight temporal engineering targets for altering final biomass composition to increase the value of soybeans and a path to breaking the inverse correlation between seed protein and oil content.

HighlightFatty acid composition determines oil qualities. Not only the selectivity of BnDGAT1 enzymes, but also the concentration of the fatty acid substrates, determines the oil composition in Brassica napus seeds.

The ability to transform Camelina sativa easily with biosynthetic enzymes derived from other plants has made this oil seed crop an ideal platform for the production of unusual lipids valuable for different applications. However, in addition to expressing transgenic enzymes, the suppression of endogenous enzyme activity to reduce competition for common substrates or cofactors is also required to enhance the production of target compounds. As camelina possesses a relatively undifferentiated hexaploid genome, up to three gene homeologs can code for any particular enzymatic activity, complicating efforts to alter endogenous biosynthetic pathways. New genome editing technologies, such as that offered by the CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein) system, offer the capability to introduce mutations into specifically targeted genomic sites. Here, by using a carefully designed guide RNA identical to all three homeologs, we demonstrate the ability of the CRISPR/Cas genome editing system to introduce mutations in all three CsDGAT1 or CsPDAT1 homeologous genes important for triacylglycerol (TAG) synthesis in developing seeds. Sequence analysis from transgenic T1 plants revealed that each CsDGAT1 or each CsPDAT1 homeolog was altered by multiple mutations, resulting in a genetic mosaic in the plants. Interestingly, seed harvested from both CsDGAT1- and CsPDAT1-targeted lines was often shrunken and wrinkled. Further, lipid analysis revealed that many lines produced seed with reduced oil content and altered fatty acid composition, consistent with the role of the targeted genes in seed oil biosynthesis. The CRISPR/Cas system therefore represents a useful method to alter endogenous biosynthetic pathways efficiently in polyploid species such as camelina.

Camelina (Camelina sativa L. Crantz) is an alternative oilseed crop with potential for fallow replacement in dryland cerealbased crop production systems in the semiarid Great Plains. Th e interaction between genotype and environment was investigated on camelina seed yield, oil content, and fatty acid composition across two locations in the U.S. Great Plains. Treatments were three spring camelina genotypes (cultivars Blaine Creek, Pronghorn, and Shoshone), three growing seasons (2013, 2014, and 2015) and two locations (at Hays, KS, and Moccasin, MT). Results showed camelina grown at Hays yielded 54% less than that at Moccasin. Blaine Creek yielded 17 and 42% more than Pronghorn and Shoshone at Hays but yields were not diff erent among genotypes at Moccasin. Oil content ranged from 262 g kg -1 at Hays to 359 g kg -1 at Moccasin. Th e proportion of polyunsaturated fatty acids (PUFAs) ranged from 51% at Hays to 55% at Moccasin, whereas monounsaturated fatty acid (MUFA) and saturated fatty acid (SFA) contents were greater at Hays. Th e linolenic acid content ranged from 26% when Pronghorn was planted at Hays to 35% when planted at Moccasin. In general, the variations in seed yield and fatty acid profi le corresponded well with growing season precipitation and temperatures at each environment.

Long chain fatty acid synthetases (LACSs) activate the fatty acid chains produced by plastidial de novo biosynthesis to generate acyl-CoA derivatives, important intermediates in lipid metabolism. Oilseeds, like sunflower, accumulate high levels of triacylglycerols (TAGs) in their seeds to nourish the embryo during germination. This requires that sunflower seed endosperm supports very active glycerolipid synthesis during development. Sunflower seed plastids produce large amounts of fatty acids, which must be activated through the action of LACSs, in order to be incorporated into TAGs. We cloned two different LACS genes from developing sunflower endosperm, HaLACS1 and HaLACS2, which displayed sequence homology with Arabidopsis LACS9 and LACS8 genes, respectively. These genes were expressed at high levels in developing seeds and exhibited distinct subcellular distributions. We generated constructs in which these proteins were fused to green fluorescent protein and performed transient expression experiments in tobacco cells. The HaLACS1 protein associated with the external envelope of tobacco chloroplasts, whereas HaLACS2 was strongly bound to the endoplasmic reticulum. Finally, both proteins were overexpressed in Escherichia coli and recovered as active enzymes in the bacterial membranes. Both enzymes displayed similar substrate specificities, with a very high preference for oleic acid and weaker activity toward stearic acid. On the basis of our findings, we discuss the role of these enzymes in sunflower oil synthesis.