Up‐regulation of lipid biosynthesis increases the oil content in leaves of Sorghum bicolor

Abstract

Synthesis and accumulation of the storage lipid triacylglycerol in vegetative plant tissues has emerged as a promising strategy to meet the world's future need for vegetable oil. Sorghum (Sorghum bicolor) is a particularly attractive target crop given its high biomass, drought resistance and C photosynthesis. While oilseed-like triacylglycerol levels have been engineered in the C model plant tobacco, progress in C monocot crops has been lagging behind. In this study, we report the accumulation of triacylglycerol in sorghum leaf tissues to levels between 3 and 8.4% on a dry weight basis depending on leaf and plant developmental stage. This was achieved by the combined overexpression of genes encoding the Zea mays WRI1 transcription factor, Umbelopsis ramanniana UrDGAT2a acyltransferase and Sesamum indicum Oleosin-L oil body protein. Increased oil content was visible as lipid droplets, primarily in the leaf mesophyll cells. A comparison between a constitutive and mesophyll-specific promoter driving WRI1 expression revealed distinct changes in the overall leaf lipidome as well as transitory starch and soluble sugar levels. Metabolome profiling uncovered changes in the abundance of various amino acids and dicarboxylic acids. The results presented here are a first step forward towards the development of sorghum as a dedicated biomass oil crop and provide a basis for further combinatorial metabolic engineering.

A Versatile High Throughput Screening Platform for Plant Metabolic Engineering Highlights the Major Role of ABI3 in Lipid Metabolism Regulation

“…For example, the "Leaf Oil" platform technology, which allows plants to accumulate oil in all vegetative organs with yields potentially exceeding those of canola and oil palm, was quickly developed thanks to an extensive number of design-built-test-learn cycles (Vanhercke et al, 2013(Vanhercke et al, , 2014El Tahchy et al, 2017) that strongly relied on an efficient use of the agroinfiltration-based system. The technology is continuously being upgraded by further cycles to create tailor-made products for biofuel applications (Reynolds et al, 2015;Reynolds et al, 2017), and is also being transferred to a range of major crops such as sugarcane (Zale et al, 2016), maize (Alameldin et al, 2017) and Sorghum bicolor (Vanhercke et al, 2019). Such high biomass crops have the potential to become a future sustainable and abundant supply of plant oils for food, feed, biofuel and oleo-chemical applications (Rahman et al, 2016;Weselake, 2016).…”

Sorghum bicolorcultivars have divergent and dynamic gene regulatory networks that control the temporal expression of genes in stem tissue

“…Other proof-of-concept studies for increasing TAGs in vegetative tissues have been performed in Arabidopsis thaliana, Brachypodium distachyon, Nicotiana benthamiana, Nicotiana tabacum , sugarcane ( Saccharum spp. ), and Sorghum bicolor (Thelen and Ohlrogge, 2002; Fan, Yan and Xu, 2013; Vanhercke et al , 2013, 2019; Yang et al , 2015; Zale et al , 2016; Mitchell et al , 2020; Parajuli et al , 2020; Xu et al , 2020). For example, in engineered sugarcane, TAGs accumulated to an average of 8.0% of the dry weight of leaves and 4.3% of the dry weight of stems (Huang, Long and Singh, 2015; Zale et al , 2016; Parajuli et al , 2020).…”

“…Another study in tobacco achieved TAGs accumulation up to 19% of the dry weight of the total biomass production by over-expressing the genes encoding WRINKLED1, DGAT, and oleosins (Vanhercke et al , 2014; Zale et al , 2016). However, many of these engineering efforts to increase TAG accumulation in immature vegetative tissues have resulted in negative impacts on plant growth as observed in sorghum, potato, tobacco, and Arabidopsis (Slocombe et al , 2009; Feltus and Vandenbrink, 2012; Kelly et al , 2013; Vanhercke et al , 2014, 2019; Hofvander et al , 2016; Liu et al , 2017; Ramšak et al , 2018; Xiaoyu Xu et al , 2019; Xu et al , 2020; Mitchell et al , 2020). One hypothesis is that driving lipid accumulation under the control of tissue- and/or developmental-stage specific promoters, specifically those active during late development (Moyle and Birch, 2013; Mudge et al , 2013), will have less of an impact on photosynthetic efficiencies and plant growth than constitutive overexpression of genes of interest.…”

A Synergistic Genetic Engineering Strategy Induced Triacylglycerol Accumulation in Potato (Solanum tuberosum) Leaf

“…Up to 15% TAG in leaf dry weight (DW) was accumulated in transgenic tobacco (Nicotiana tabacum) through the simultaneous overexpression of A. thaliana WRINKLED1 (AtWRI1), A. thaliana diacylglycerol acyltransferase1 (AtDGAT1) and sesame (Sesamum indicum) OLEOSIN1 (SiOLEOSIN1) genes (Vanhercke et al, 2014a), coined the 'Push, Pull and Protect' synergistic strategy for oil increase (Vanhercke et al, 2014b). In addition, the C 4 plant sorghum (Sorghum bicolor) was recently reported to produce between 3 and 8.4% of TAG by DW in vegetative tissues following coexpression of Zea mays WRI1, Umbelopsis ramanniana DGAT2a, and SiOLEOSIN (Vanhercke et al, 2018). Further enhancement of TAG accumulation was achieved by downregulating the TAG-specific lipase sugar-dependent 1 (SDP1) gene, which resulted in doubled TAG production (30% of DW) in transgenic tobacco leaf (Vanhercke et al, 2017), while sugarcane (Saccharum officinarum) engineered with the similar methodology also displayed a 95-fold enhancement of TAG content in vegetative tissues (Zale et al, 2016).…”