The mechanism by which plants synthesize and store high amounts of triacylglycerols (TAG) in tissues other than seeds is not well understood. The comprehension of controls for carbon partitioning and oil accumulation in nonseed tissues is essential to generate oil-rich biomass in perennial bioenergy crops. Persea americana (avocado), a basal angiosperm with unique features that are ancestral to most flowering plants, stores ~ 70 % TAG per dry weight in its mesocarp, a nonseed tissue. Transcriptome analyses of select pathways, from generation of pyruvate and leading up to TAG accumulation, in mesocarp tissues of avocado was conducted and compared with that of oil-rich monocot (oil palm) and dicot (rapeseed and castor) tissues to identify tissue- and species-specific regulation and biosynthesis of TAG in plants. RNA-Seq analyses of select lipid metabolic pathways of avocado mesocarp revealed patterns similar to that of other oil-rich species. However, only some predominant orthologs of the fatty acid biosynthetic pathway genes in this basal angiosperm were similar to those of monocots and dicots. The accumulation of TAG, rich in oleic acid, was associated with higher transcript levels for a putative stearoyl-ACP desaturase and endoplasmic reticulum (ER)-associated acyl-CoA synthetases, during fruit development. Gene expression levels for enzymes involved in terminal steps to TAG biosynthesis in the ER further indicated that both acyl-CoA-dependent and -independent mechanisms might play a role in TAG assembly, depending on the developmental stage of the fruit. Furthermore, in addition to the expression of an ortholog of WRINKLED1 (WRI1), a regulator of fatty acid biosynthesis, high transcript levels for WRI2-like and WRI3-like suggest a role for additional transcription factors in nonseed oil accumulation. Plastid pyruvate necessary for fatty acid synthesis is likely driven by the upregulation of genes involved in glycolysis and transport of its intermediates. Together, a comparative transcriptome analyses for storage oil biosynthesis in diverse plants and tissues suggested that several distinct and conserved features in this basal angiosperm species might contribute towards its rich TAG content. Our work represents a comprehensive transcriptome resource for a basal angiosperm species and provides insight into their lipid metabolism in mesocarp tissues. Furthermore, comparison of the transcriptome of oil-rich mesocarp of avocado, with oil-rich seed and nonseed tissues of monocot and dicot species, revealed lipid gene orthologs that are highly conserved during evolution. The orthologs that are distinctively expressed in oil-rich mesocarp tissues of this basal angiosperm, such as WRI2, ER-associated acyl-CoA synthetases, and lipid-droplet associated proteins were also identified. This study provides a foundation for future investigations to increase oil-content and has implications for metabolic engineering to enhance storage oil content in nonseed tissues of diverse species.

Thirty years ago, the discovery of a cannabinoid (CB) receptor that interacts with the psychoactive compound in Cannabis led to the identification of anandamide, an endogenous receptor ligand or endocannabinoid. Research on endocannabinoids has since exploded, and additional receptors along with their lipid mediators and signaling pathways continue to be revealed. Specifically, in humans, the release of endocannabinoids from membrane lipids occurs on demand and the signaling process is rapidly attenuated by the breakdown of the ligand suggesting a tight regulation of the endocannabinoid system (ECS). Additionally, the varying distribution of CB receptors between the central nervous system and other tissues allows for the ECS to participate in a wide range of cognitive and physiological processes. Select plant-derived ‘phyto’cannabinoids such as Δ-9-tetrahydrocannabinol (Δ⁹-THC) bind to the CB receptors and trigger the ECS, and in the case of Δ⁹-THC, while it has therapeutic value, can also produce detrimental effects. Current research is aimed at the identification of additional phytocannabinoids with minimal psychotropic effects with potential for therapeutic development. Although decades of research on the ECS and its components have expanded our understanding of the mechanisms and implications of endocannabinoid signaling in mammals, it continues to evolve. Here, we provide a brief overview of the ECS and its overlap with other related lipid-mediated signaling pathways.

Tree peony (Paeonia section Moutan DC.) species are woody oil crops with high unsaturated fatty acid content, including α-linolenic acid (ALA/18:3; >40% of the total fatty acid). Comparative transcriptome analyses were carried out to uncover the underlying mechanisms responsible for high and low ALA content in the developing seeds of P. rockii and P. lutea, respectively. Expression analysis of acyl lipid metabolism genes revealed upregulation of select genes involved in plastidial fatty acid synthesis, acyl editing, desaturation, and triacylglycerol assembly in seeds of P. rockii relative to P. lutea. Also, in association with ALA content in seeds, transcript levels for fatty acid desaturases (SAD, FAD2, and FAD3), which encode enzymes necessary for polyunsaturated fatty acid synthesis, were higher in P. rockii compared to P. lutea. Furthermore, the overexpression of PrFAD2 and PrFAD3 in Arabidopsis increased linoleic and ALA content, respectively, and modulated the final ratio 18:2/18:3 in the seed oil. In conclusion, we identified the key steps and validated the necessary desaturases that contribute to efficient ALA synthesis in a woody oil crop. Together, these results will aid to increase essential fatty acid content in seeds of tree peonies and other crops of agronomic interest.

Iris sanguinea is a perennial flowering plant that is typically cultivated through seeds or bulbs. However, due to limitations in conventional propagation, an alternate regeneration system using seeds was developed. The protocol included optimization of sterilization, stratification and scarification methods as iris seeds exhibit physiological dormancy. In addition to chlorine-based disinfection, alkaline or heat treatment was used to break seed dormancy and reduce contamination. When seeds were soaked in water at 80 °C overnight, and sterilized with 75% EtOH for 30 s and 4% NaOCl solution for 20 minutes, contamination was reduced to 10% and a 73.3% germination was achieved. The germinated seedlings with 2-3 leaves and radicle were used as explants to induce adventitious buds. The optimal MS medium with 0.5 mg L⁻¹ 6-benzylaminopurine, 0.2 mg L⁻¹ NAA, and 1.0 mg L⁻¹ kinetin resulted in 93.3% shoot induction and a proliferation coefficient of 5.30. Medium with 0.5 mg L⁻¹ NAA achieved 96.4% rooting of the adventitious shoots. The survival rate was more than 90% after 30 days growth in the cultivated matrix. In conclusion, a successful regeneration system for propagation of I. sanguinea was developed using seeds, which could be utilized for large-scale propagation of irises of ecological and horticultural importance.

In higher plants, acyl-CoA:diacylglycerol acyltransferase (DGAT) and phospholipid:diacylglycerol acyltransferase (PDAT) catalyze the terminal step of triacylglycerol (TAG) synthesis in acyl-CoA-dependent and -independent pathways, respectively. Avocado (Persea americana) mesocarp, a nonseed tissue, accumulates significant amounts of TAG (~70% by dry weight) that is rich in heart-healthy oleic acid (18:1). The oil accumulation stages of avocado mesocarp development coincide with high expression levels for type-1 DGAT (DGAT1) and PDAT1, although type-2 DGAT (DGAT2) expression remains low. The strong preference for oleic acid demonstrated by the avocado mesocarp TAG biosynthetic machinery represents lucrative biotechnological opportunities, yet functional characterization of these three acyltransferases has not been explored to date. We expressed avocado PaDGAT1, PaDGAT2, and PaPDAT1 in bakers’ yeast and leaves of Nicotiana benthamiana. PaDGAT1 complemented the TAG biosynthesis deficiency in the quadruple mutant yeast strain H1246, and substantially elevated total cellular lipid content. In vitro enzyme assays showed that PaDGAT1 prefers oleic acid compared to palmitic acid (16:0). Both PaDGAT1 and PaPDAT1 increased the lipid content and elevated oleic acid levels when expressed independently or together, transiently in N. benthamiana leaves. These results indicate that PaDGAT1 and PaPDAT1 prefer oleate-containing substrates, and their coordinated expression likely contributes to sustained TAG synthesis that is enriched in oleic acid. This study establishes a knowledge base for future metabolic engineering studies focused on exploitation of the biochemical properties of PaDGAT1 and PaPDAT1.