Storing carbon in leaf lipid sinks enhances perennial ryegrass carbon capture especially under high N and elevated CO2

Abstract

By modifying two genes involved in lipid biosynthesis and storage [cysteine oleosin (cys-OLE)/diacylglycerol O-acyltransferase (DGAT)], the accumulation of stable lipid droplets in perennial ryegrass (Lolium perenne) leaves was achieved. Growth, biomass allocation, leaf structure, gas exchange parameters, fatty acids, and water-soluble carbohydrates were quantified for a high-expressing cys-OLE/DGAT ryegrass transformant (HL) and a wild-type (WT) control grown under controlled conditions with 1–10 mM nitrogen (N) supply at ambient and elevated atmospheric CO2. A dramatic shift in leaf carbon (C) storage occurred in HL leaves, away from readily mobilizable carbohydrates and towards stable lipid droplets. HL exhibited an increased growth rate, mainly in non-photosynthetic organs, leading to a decreased leaf mass fraction. HL leaves, however, displayed an increased specific leaf area and photosynthetic rate per unit leaf area, delivering greater overall C capture and leaf growth at high N supply. HL also exhibited a greater photosynthesis response to elevated atmospheric CO2. We speculate that by behaving as uniquely stable microsinks for C, cys-OLE-encapsulated lipid droplets can reduce feedback inhibition of photosynthesis and drive greater C capture. Manipulation of many genes and gene combinations has been used to increase non-seed lipid content. However, the cys-OLE/DGAT technology remains the only reported case that increases plant biomass. We contrast cys-OLE/DGAT with other lipid accumulation strategies and discuss the implications of introducing lipid sinks into non-seed organs for plant energy homeostasis and growth.

Adjustment of Photosynthetic and Antioxidant Activities to Water Deficit Is Crucial in the Drought Tolerance of Lolium multiflorum/Festuca arundinacea Introgression Forms

“…It was suggested earlier that carbon metabolism could trigger TAG accumulation in plants. This phenomenon was reported previously for forage grasses [32,57,58].…”

Will rising atmosphericCO2concentration inhibit nitrate assimilation in shoots but enhance it in roots ofC3plants?

“…The increase in total plant DW relative to total plant N and the resultant decrease in tissue N per unit DW at elevated CO 2 has been termed ‘N dilution’ and has been linked to increased accumulation of non‐structural carbohydrates and plant secondary compounds (Taub and Wang ). In some cases, elevated CO 2 can increase photosynthesis in the short term, but if photosynthate utilisation is inadequate, a source sink imbalance can arise, leading to end‐product (carbohydrate) accumulation and subsequent down‐regulation of photosynthesis linked to lower ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) concentration and activity (Ainsworth and Rogers , Zheng et al , Beechey‐Gradwell et al ). In their Summary, Bloom et al () stated that ‘hundreds of papers’ support their proposal that rising atmospheric CO 2 concentrations inhibit malate production in chloroplasts and thus impede assimilation of NO 3 − into protein in shoots of C 3 plants.…”

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.…”