Digital Gene Expression Profiling to Explore Differentially Expressed Genes Associated with Terpenoid Biosynthesis during Fruit Development in Litsea cubeba

LcWRKY17, a WRKY Transcription Factor from Litsea cubeba, Effectively Promotes Monoterpene Synthesis

The WRKY gene family is one of the most significant transcription factor (TF) families in higher plants and participates in many secondary metabolic processes in plants. Litsea cubeba (Lour.) Person is an important woody oil plant that is high in terpenoids. However, no studies have been conducted to investigate the WRKY TFs that regulate the synthesis of terpene in L. cubeba. This paper provides a comprehensive genomic analysis of the LcWRKYs. In the L. cubeba genome, 64 LcWRKY genes were discovered. According to a comparative phylogenetic study with Arabidopsis thaliana, these L. cubeba WRKYs were divided into three groups. Some LcWRKY genes may have arisen from gene duplication, but the majority of LcWRKY evolution has been driven by segmental duplication events. Based on transcriptome data, a consistent expression pattern of LcWRKY17 and terpene synthase LcTPS42 was found at different stages of L. cubeba fruit development. Furthermore, the function of LcWRKY17 was verified by subcellular localization and transient overexpression, and overexpression of LcWRKY17 promotes monoterpene synthesis. Meanwhile, dual-Luciferase and yeast one-hybrid (Y1H) experiments showed that the LcWRKY17 transcription factor binds to W-box motifs of LcTPS42 and enhances its transcription. In conclusion, this research provided a fundamental framework for future functional analysis of the WRKY gene families, as well as breeding improvement and the regulation of secondary metabolism in L. cubeba.

Role of Litsea cubeba Essential Oil in Agricultural Products Safety: Antioxidant and Antimicrobial Applications

The essential oil from Litsea cubeba (LCEO) has good antioxidant, antimicrobial, anti-insect properties, which gives it the potential for use as a natural additive to food resources and food products in order to prevent spoilage and extend shelf life. In this study the biological activity related to food preservation was observed. The main volatile organic compounds were geranial (39.4%), neral (29.5%), and limonene (14.3%). Antioxidant activity was 30.9%, which was equal to 167.94 µg of Trolox per mL of sample. Antimicrobial activity showed the strongest inhibition against Serratia marcescens by disk diffusion method and minimum inhibitory concentrations MIC 50 and MIC 90 were the lowest for Micrococcus luteus with values 1.46 and 3.52 µL/mL, respectively. Antimicrobial activity of the LCEO vapor phase showed strong inhibition of microorganisms on apples, pears, potatoes, and kohlrabies. Over 50% of gram-positive and gram-negative bacteria and yeasts were inhibited by a concentration of 500 µL/mL. The inhibition of microorganisms was concentration dependent. Anti-insect activity was also strong, with 100% lethality of Pyrrhocoris apterus at a concentration of 25%. These results suggest that LCEO could be potentially used as a food preservative.

Overexpression of the 3-hydroxy-3-methylglutaryl-CoA synthase gene LcHMGS effectively increases the yield of monoterpenes and sesquiterpenes

Monoterpenes are important components of plant essential oils and have long been used as raw materials for spices and food flavorings. A number of studies have been performed to increase the content of monoterpenes in plants, but no obvious effect was observed. Exchange was observed between the methylerythritol phosphate (MEP) and mevalonic acid (MVA) metabolic pathways, which produce monoterpenes and sesquiterpenes, respectively. However, the specific details of the communication have not been elucidated. In the present study, we investigated the effects of overexpressing Litsea cubeba (Lour.) Persoon 3-hydroxy-3-methylglutaryl-coenzyme A synthase (LcHMGS) on the production of monoterpenes and sesquiterpenes. In addition, we also explored the flow of metabolic flux between the MEP and MVA pathways. We cloned LcHMGS and analyzed its expression pattern in various tissues. The overexpression of LcHMGS significantly increased the species and content of monoterpenes and sesquiterpenes. In addition, LcHMGS overexpression in plants induced such phenotypes as excessive growth, enlarged vegetative organs and early flowering by elevating the GA3 content. Our results demonstrate a metabolic engineering strategy to improve the yield of monoterpenes and sesquiterpenes and simultaneously increase the biomass of plants.

Changes in the Profiles of Yield, Yield Component, Oil Content, and Citral Content in Litsea cubeba (Lour.) Persoon Following Foliar Fertilization with Zinc and Boron

Mountain pepper (Litsea cubeba (Lour.) Persoon) is an important oil plant used as an ingredient in edible oil, cooking condiments, cosmetics, pesticides, and potential biofuels. Zinc and boron are essential micronutrients for plant growth. However, the effects of zinc and boron on the yield, yield component, oil content, and citral content in L. cubeba have not been determined. This study was conducted to evaluate the efficacy of the foliar application of zinc, boron, and multiple micronutrients (zinc + boron) on the yield, yield component, oil content, and citral content of three varieties (Fuyang 1 (FY1), Jianou 2 (JO2), and Jianou 3 (JO3)) of L. cubeba. Zinc sulfate (0.25%), boric acid (0.25%), and zinc sulfate (0.25%) + boric acid (0.25%) were sprayed on selected trees at five different times at full bloom and 28 days before harvest, once every seven days. The results indicated that Zn had a negative effect on the yield, yield component, oil content, and citral content of the FY1, JO2, and JO3 varieties compared to the untreated trees. B had positive effects on the yield, yield component, oil content, and citral content of the JO2 and JO3 varieties but not on those of the FY1 variety when compared to the untreated trees. The highest levels of yield, yield component, oil content, and citral content for all three varieties were obtained with the combined application of zinc sulfate + boric acid. Hence, the foliar application of multiple micronutrients (zinc + boron) is an effective method to improve the yield, oil content, and citral content in L. cubeba. In addition, the 100-fruit weight (HFW) was positively correlated with the yield, oil content, and citral content and could be used as a tool to select new cultivars with high yield, high oil content, and high citral content under zinc sulfate, boric acid, and zinc sulfate + boric acid applications in L. cubeba.