Upregulated Lipid Biosynthesis at the Expense of Starch Production in Potato (Solanum tuberosum) Vegetative Tissues via Simultaneous Downregulation of ADP-Glucose Pyrophosphorylase and Sugar Dependent1 Expressions

Abstract

Triacylglycerol is a major component of vegetable oil in seeds and fruits of many plants, but its production in vegetative tissues is rather limited. It would be intriguing and important to explore any possibility to expand current oil production platforms, for example from the plant vegetative tissues. By expressing a suite of transgenes involved in the triacylglycerol biosynthesis, we have previously observed substantial accumulation of triacylglycerol in tobacco (Nicotiana tabacum) leaf and potato (Solanum tuberosum) tuber. In this study, simultaneous RNA interference (RNAi) downregulation of ADP-glucose pyrophosphorylase (AGPase) and Sugar-dependent1 (SDP1), was able to increase the accumulation of triacylglycerol and other lipids in both wild type potato and the previously generated high oil potato line 69. Particularly, a 16-fold enhancement of triacylglycerol production was observed in the mature transgenic tubers derived from the wild type potato, and a two-fold increase in triacylglycerol was observed in the high oil potato line 69, accounting for about 7% of tuber dry weight, which is the highest triacylglycerol accumulation ever reported in potato. In addition to the alterations of lipid content and fatty acid composition, sugar accumulation, starch content of the RNAi potato lines in both tuber and leaf tissues were also substantially changed, as well as the tuber starch properties. Microscopic analysis further revealed variation of lipid droplet distribution and starch granule morphology in the mature transgenic tubers compared to their parent lines. This study reflects that the carbon partitioning between lipid and starch in both leaves and non-photosynthetic tuber tissues, respectively, are highly orchestrated in potato, and it is promising to convert low-energy starch to storage lipids via genetic manipulation of the carbon metabolism pathways.

Cassava shrunken-2 homolog MeAPL3 determines storage root starch and dry matter content and modulates storage root postharvest physiological deterioration

“…6 and 7). This is consistent with other studies of shrunken-2 in maize (Bhave et al 1990), rice APL2 (Lee et al 2007), and RNAi suppression lines (Xu et al 2019). An interesting associated observation was an increase in average storage root number per plant in lines with reduced starch and DMC.…”

Inactivation of rice starch branching enzyme IIb triggers broad and unexpected changes in metabolism by transcriptional reprogramming

“…For example, starch deficiency in Arabidopsis thaliana resulted in the accumulation of sugars and significantly increased fatty acid synthesis via the modulation of acetyl-CoA carboxylase activity (62). The down-regulation of AGPase also increased fatty acid accumulation in sugarcane and potato (63,64). In the rice floury shrunken endosperm 1 (fse1) mutant, the reduction in total starch and amylose levels was complemented by a ∼48% increase in total lipids (65).…”

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

“…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.…”