Development of Vegetative Oil Sorghum: From Lab-to-Field
Biomass crops engineered to accumulate energy-dense triacylglycerols (TAG or “vegetable oils”) in their vegetative tissues have emerged as potential feedstocks to meet the growing demand for renewable diesel and sustainable aviation fuel (SAF). Unlike oil palm and oilseed crops, the current commercial sources of TAG, vegetative tissues, such as leaves and stems, only transiently accumulate TAG. In this report, we used grain (Texas430 or TX430) and sugar-accumulating “sweet” (Ramada) genotypes of sorghum, a high-yielding, environmentally resilient biomass crop, to accumulate TAG in leaves and stems. We initially tested several gene combinations for a “push-pull-protect" strategy. The top TAG-yielding constructs contained five oil transgenes for a sorghum Wrinkled1 transcription factor (“push”), a Cuphea viscosissima diacylglycerol acyltransferase (DGAT; "pull"), a modified sesame oleosin (“protect”) and two combinations of specialized Cuphea lysophosphatidic acid acyltransferases and medium-chain acyl-acyl carrier protein thioesterases. Though intended to generate oils with medium-chain fatty acids, engineered lines accumulated oleic acid-rich oil to amounts of up to 2.5% DW in leaves and 2.0% DW in stems in the greenhouse, 36-fold and 49-fold increases relative to wild-type plants, respectively. Under field conditions, the top-performing event accumulated TAG to amount of up to 5.5% DW in leaves and 3.5% DW in stems, 78-fold and 58-fold increases, respectively, relative to wild-type TX430. Transcriptomic and fluxomic analyses revealed potential bottlenecks for increased TAG accumulation. Overall, our studies highlight the utility of a lab-to-field pipeline coupled with systems biology studies to deliver high vegetative oil sorghum for SAF and renewable diesel production. Overall design: RNAseq was conducted to compare changes in trascriptome between WT and TAG-producing transgenic event. Field is located at Eastern Nebraska Research and Education Center (ENREC) in Mead, NE, USA (41°08'42.7"N 96°26'20.5"W). Total RNA was extracted using field-grown mature leaves at early reproductive stage in 2021. No additional treatment applied to the field or plants.