Increasing growth and yield by altering carbon metabolism in a transgenic leaf oil crop

Abstract

Summary Engineering high biomass plants that produce oil (triacylglycerol or TAG) in vegetative rather than seed‐related tissues could help meet our growing demand for plant oil. Several studies have already demonstrated the potential of this approach by creating transgenic crop and model plants that accumulate TAG in their leaves and stems. However, TAG synthesis may compete with other important carbon and energy reserves, including carbohydrate production, and thereby limit plant growth. The aims of this study were thus: first, to investigate the effect of TAG accumulation on growth and development of previously generated high leaf oil tobacco plants; and second, to increase plant growth and/or oil yields by further altering carbon fixation and partitioning. This study showed that TAG accumulation varied with leaf and plant developmental stage, affected leaf carbon and nitrogen partitioning and reduced the relative growth rate and final biomass of high leaf oil plants. To overcome these growth limitations, four genes related to carbon fixation (encoding CBB cycle enzymes SBPase and chloroplast‐targeted FBPase) or carbon partitioning (encoding sucrose biosynthetic enzyme cytosolic FBPase and lipid‐related transcription factor DOF4) were overexpressed in high leaf oil plants. In glasshouse conditions, all four constructs increased early growth without affecting TAG accumulation while chloroplast‐targeted FBPase and DOF4 also increased final biomass and oil yields. These results highlight the reliance of plant growth on carbon partitioning, in addition to carbon supply, and will guide future attempts to improve biomass and TAG accumulation in transgenic leaf oil crops.

Changes in Leaf-Level Nitrogen Partitioning and Mesophyll Conductance Deliver Increased Photosynthesis for Lolium perenne Leaves Engineered to Accumulate Lipid Carbon Sinks

“…Alternatively, it may be that some technologies impose too small a sink to affect photosynthesis, especially if oils are not protected and are rapidly degraded within the leaf. Conversely, too great a sink could create excessive competition for carbon, which could hinder plant development ( Mitchell et al, 2020 ). Finally, the use of global transcription factors to enhance oil accumulation may have unintended pleiotropic effects and could impede normal cellular function ( Grimberg et al, 2015 ).…”

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

“…However, the cost associated with production of fuels and other bioproducts from plant biomass is relatively high, which has been a major constraint on the widespread adoption of grasses as sources of feedstock to produce biofuels or bioproducts (Hill et al , 2006; Kumar, Long and Singh, 2018). Previous work showed that C4 grasses can be genetically engineered for increased fatty acid production, resulting in biomass with high oil content (Huang, Long and Singh, 2015; Huang et al , 2016; Wang, 2016; Zale et al , 2016; Beechey-Gradwell et al , 2020; Mitchell et al , 2020; Parajuli et al , 2020), which increases their value as biofuels. Genetically engineering high-biomass grasses to accumulate valuable bioproducts that require minimal processing post-harvest is a desirable way forward, but has many challenges.…”

“…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.…”

Metabolomics and transcriptomics analyses of sugarcane variety SP80-3280 throughout development in the field

“…During plant development, plants need to respond to developmental and environmental signals in their internal and external environments by relying on the activity of a variety of cellular components, such as for example metabolites, that trigger the appropriate metabolic responses needed for survival (Krzyzaniak et al, 2018;Matilla, 2018). It has been well described that plants have the ability to produce large amounts and a wide variety of metabolites that are important role players in their development and in response to changes in their environment (Bhatla, 2018;Bhatla & Lal, 2018;Mitchell et al, 2020), be it internal or external. These small molecules (< 1.800 Da) form the basis of crop yield and quality (Gatehouse, 2004).…”