Engineered poplar for bioproduction of the triterpene squalene.

Building sustainable platforms to produce biofuels and specialty chemicals has become an increasingly important strategy to supplement and replace fossil fuels and petrochemical-derived products. Terpenoids are the most diverse class of natural products that have many commercial roles as specialty chemicals. Poplar is a fast growing, biomassdense bioenergy crop with many species known to produce large amounts of the hemiterpene isoprene, suggesting an inherent capacity to produce significant quantities of other terpenes. Here we aimed to engineer poplar with optimized pathways to produce squalene, a triterpene commonly used in cosmetic oils, a potential biofuel candidate, and the precursor to the further diversified classes of triterpenoids and sterols. The squalene production pathways were either re-targeted from the cytosol to plastids or co-produced with lipid droplets in the cytosol. Squalene and lipid droplet co-production appeared to be toxic, which we hypothesize to be due to disruption of adventitious root formation, suggesting a need for tissue specific production. Plastidial squalene production enabled up to 0.63 mg/g fresh weight in leaf tissue, which also resulted in reductions in isoprene emission and photosynthesis. These results were also studied through a technoeconomic analysis, providing further insight into developing poplar as a production host.

Acetic acid: a cheap but chief metabolic regulator for abiotic stress tolerance in plants.

As sessile organisms, plants constantly face a variety of abiotic stresses, such as drought, salinity, and metal/metalloid toxicity, all of which possess significant threats to plant growth and yield potential. Improving plant resilience to such abiotic stresses bears paramount importance in practicing sustainable agriculture worldwide. Acetic acid/acetate has been recognized as an important metabolite with multifaceted roles in regulating plant adaptation to diverse abiotic stresses. Recent studies have elucidated that acetic acid can potentiate plants' inherent mechanisms to withstand the adverse effects of abiotic stresses through the regulation of lipid metabolism, hormone signaling, epigenetic changes, and physiological defense mechanisms. Numerous studies also underpin the potential use of acetic acid in boosting crop production under unfavorable environmental conditions. This review provides a comprehensive update on the understanding of how acetic acid regulates plant photosynthesis, acts as an antitranspirant, detoxifies reactive oxygen species to alleviate oxidative stress, interacts with phytohormones to regulate physiological processes, and improves soil fertility and microbial diversity, with a specific focus on drought, salinity, and metal toxicity. We also highlight the eco-friendly and economic potential of acetic acid that may attract farmers from developing countries to harness the benefits of acetic acid application for boosting abiotic stress resistance in crops. Given that acetic acid is a widely accessible, inexpensive, and eco-friendly compound, the revelation of acetic acid-mediated regulatory pathways and its crosstalk with other signaling molecules will have significant importance in developing a sustainable strategy for mitigating abiotic stresses in crops.