Sweet Basil Has Distinct Synthases for Eugenol Biosynthesis in Glandular Trichomes and Roots with Different Regulatory Mechanisms

Increase of secondary metabolites in sweet basil (Ocimum basilicum L.) leaves by exposure to N2O5 with plasma technology

Exposure to N2O5 generated by plasma technology activates immunity in Arabidopsis through tryptophan metabolites. However, little is known about the effects of N2O5 exposure on other plant species. Sweet basil synthesizes many valuable secondary metabolites in its leaves. Therefore, metabolomic analyses were performed at three different exposure levels [9.7 (Ex1), 19.4 (Ex2) and 29.1 (Ex3) μmol] to assess the effects of N2O5 on basil leaves. As a result, cinnamaldehyde and phenolic acids increased with increasing doses. Certain flavonoids, columbianetin, and caryophyllene oxide increased with lower Ex1 exposure, cineole and methyl eugenol increased with moderate Ex2 exposure and L-glutathione GSH also increased with higher Ex3 exposure. Furthermore, gene expression analysis by quantitative RT-PCR showed that certain genes involved in the syntheses of secondary metabolites and jasmonic acid were significantly up-regulated early after N2O5 exposure. These results suggest that N2O5 exposure increases several valuable secondary metabolites in sweet basil leaves via plant defense responses in a controllable system.

Transcriptome-wide analysis of PIP reductase gene family identified a phenylpropene synthase crucial for the biosynthesis of dibenzocyclooctadiene lignans in Schisandra chinensis

Phenylpropenes, such as isoeugenol and eugenol, are produced as defend compounds, floral attractants, and flavor constituents by phenylpropene synthases belonging to the PIP reductase family. Moreover, isoeugenol is proposed to be involved in the biosynthesis of dibenzocyclooctadiene lignans, the main active compounds of Schisandra chinensis (Turcz.) Baill. fruits (SCF). S. chinensis, a woody vine plant, is widely used for its medicinal, horticultural, edible, and economic values. In this study, nine ScPIP genes were identified and characterized from the transcriptome datasets of SCF. The expression profiles revealed that ScPIP genes were differentially expressed during different developmental stages of SCF. Three ScPIPs were selected and cloned as candidate genes encoding phenylpropene synthases according to phylogenetic analysis. ScPIP1 was proved to function as isoeugenol synthase (IGS) and designated as ScIGS1 through in vivo functional characterization in Escherichia coli. Subcellular localization analysis demonstrated that ScIGS1 was localized in both the cytoplasm and nucleus. The three-dimensional (3D) model of ScIGS1 was obtained using homology modeling. Site-directed mutagenesis experiments revealed that the substitution of residues at positions 110 and 113 impacted the product specificity of ScIGS1 and the mutation of Lys157 to Ala abolishing catalytic function. Moreover, the kcat values of mutants were lower than that of ScIGS1 using a deep learning approach. In conclusion, this study provides a basis for further research on PIP reductases and the biosynthetic pathway of dibenzocyclooctadiene lignans.

Exploring the co-operativity of secretory structures for defense and pollination in flowering plants

MAIN CONCLUSION

In flowers multiple secretory systems cooperate to deliver specialized metabolites to support specific roles in defence and pollination. The collective roles of cell types, enzymes, and transporters are discussed. The interplay between reproductive strategies and defense mechanisms in flowering plants has long been recognized, with trade-offs between investment in defense and reproduction predicted. Glandular trichomes and secretory cavities or ducts, which are epidermal and internal structures, play a pivotal role in the secretion, accumulation, and transport of specialized secondary metabolites, and contribute significantly to defense and pollination. Recent investigations have revealed an intricate connection between these two structures, whereby specialized volatile and non-volatile metabolites are exchanged, collectively shaping their respective ecological functions. However, a comprehensive understanding of this profound integration remains largely elusive. In this review, we explore the secretory systems and associated secondary metabolism primarily in Asteraceous species to propose potential shared mechanisms facilitating the directional translocation of these metabolites to diverse destinations. We summarize recent advances in our understanding of the cooperativity between epidermal and internal secretory structures in the biosynthesis, secretion, accumulation, and emission of terpenes, providing specific well-documented examples from pyrethrum (Tanacetum cinerariifolium). Pyrethrum is renowned for its natural pyrethrin insecticides, which accumulate in the flower head, and more recently, for emitting an aphid alarm pheromone. These examples highlight the diverse specializations of secondary metabolism in pyrethrum and raise intriguing questions regarding the regulation of production and translocation of these compounds within and between its various epidermal and internal secretory systems, spanning multiple tissues, to serve distinct ecological purposes. By discussing the cooperative nature of secretory structures in flowering plants, this review sheds light on the intricate mechanisms underlying the ecological roles of terpenes in defense and pollination.

Genetic and Transcriptome Analysis of Leaf Trichome Development in Chinese Cabbage (Brassica rapa L. subsp. pekinensis) and Molecular Marker Development

Chinese cabbage (Brassica rapa L. subsp. pekinensis) is one of the vegetables with the largest cultivated area in China and has been a great addition to the daily diet of Chinese people. A genetic map has been constructed in our previous study using the F₂ population of two inbred lines of Chinese cabbage, namely "G291" (a hairy line) and "ZHB" (a hairless line), based on which a candidate gene related to trichome traits was identified on chromosome A06 with a phenotypic variance of 47%. A molecular marker was found to co-segregate with the trichome traits of the F₂ population, which is in the 5'-flanking region of BrGL1, and a corresponding patent has been granted (NO. CN 108545775 B). Transcriptome analysis was carried out on the cotyledon, the first true leaf and the leaf closest to each inflorescence of F₂ individuals of "G291 × ZHB" with or without trichomes, respectively. Ten pathways, including 189 DEGs, were identified to be involved in the development of trichomes in Chinese cabbage, which may be specifically related to the development of leaf trichomes. Most of the pathways were related to the biosynthesis of the secondary metabolites, which may help plants to adapt to the ever-changing external environment. DEGs also enriched the "plant-pathogen interaction" pathway, which is consistent with the conclusion that trichomes are related to the disease resistance of plants. Our study provides a basis for future research on the occurrence and development of trichomes in Chinese cabbage.