Mapping the biosynthesis of industrially relevant fatty acids: Insights from 13C-labeling in alternative crops

To address global issues related to food and energy security, my research group is studying alternative crops, historically considered as weeds until recently being identified as promising sources of renewable specialty fuels and other industrially-relevant chemicals. Indeed, Physaria fendleri (aka. lesquerella) and Thlaspi arvense (aka. field pennycress), winter annuals closely related to Arabidopsis thaliana, produce and store in their seeds unusual fatty acids (FAs) that can replace several petrochemicals currently used in industry. Our long-term goal is to advance these plants—that can be grown off-season—as dedicated bioenergy and industrial crops. However, for these oilseed crops to become economically viable sources of unusual FAs, oil synthesis needs to be improved. A lack of knowledge of the metabolic pathways underlying FA synthesis in Physaria and pennycress seeds presents a major constraint. This study aims to find potential biochemical step(s) that limit(s) oil synthesis, which will serve as targets for future crop improvement.

To advance towards this goal, we analyzed the endosperm composition by LC-MS/MS to develop and validate culture conditions that mimic the development of the embryos in planta. Using developing Physaria and pennycress embryos in culture, we were able i) to determine the efficiency with which embryos convert substrates into biomass components, and ii) to replace the substrates by ¹³C-labeled ones and monitor the flow of ¹³C-carbon in central metabolic pathways leading to oil synthesis. Our studies demonstrated that pennycress embryos metabolize carbon into biomass with an efficiency significantly higher than other photosynthetic embryos. Interestingly, Physaria and pennycress use non-conventional pathways to channel carbon into oil. ¹³C-Metabolic Flux Analysis is ongoing to build a map of carbon flow through central metabolism. This study describes the combination of innovative tools that will pave the way for controlling seed composition in promising alternative crops.