Gene expression and induction of secondary metabolites in Nepeta cataria L. (catnip)
Creators: name: Allen, Kirsten A.
Publisher: name: No Publisher Supplied
Year: 2024

description: Catnip (Nepeta cataria L.) is an emerging medicinal and aromatic crop valued for its essential oil rich in nepetalactones. Nepeta species have numerous traditional uses across cultures and exhibit promising biological activities such as antimicrobial, antioxidant, bioherbicidal, and insect repellent properties. Many of these bioactivities are attributed to nepetalactones and other iridoid monoterpenes unique to the Nepeta genus. As commercial interest grows in catnip cultivation, strategies to enhance its production of bioactive metabolites are needed. This dissertation contributes novel insights to the growing body of work surrounding catnip and related species through the following aims: (1) investigate the effects of rooting adjuvants on the adventitious rooting of catnip stem cuttings; (2) determine the ability of salicylic acid to stimulate nepetalactone biosynthesis and induce related pathway genes in catnip; and (3) examine the untargeted metabolomic profiles of catnip flowers, leaves, and roots. Chapter 1 introduces the ethnobotanical applications of Nepeta species and their unique biochemistry. Recent discoveries have elucidated the pathways that biosynthesize nepetalactones which are regulated by iridoid synthase and nepetalactol dehydrogenase enzymes. This chapter also provides a review of the literature surrounding the use of abiotic elicitors on several species in this genus and others within the greater Lamiaceae family. Since the optimization of clonal propagation techniques is crucial for breeding programs and commercial production, Chapter 2 investigates the use of indole-3-butyric acid (IBA) and various aqueous solvents on the adventitious rooting of catnip stem cuttings. These rooting treatments neither stimulated nor inhibited catnip rooting. This is likely because catnip produces sufficient levels of endogenous auxins. This chapter also evaluates the allelochemical effects of diluted catnip essential oil (EO) on catnip, basil, and oregano stem cuttings. The EO treatments not only inhibited rooting, but also reduced the survival of these species suggesting potential herbicidal activity. Nepetalactones, iridoid monoterpenes unique to the Nepeta genus, contribute to the bioactivity of its volatile EO. Thus, Chapter 3 explores the ability of 0.5 mM and 1.0 mM salicylic acid (SA) treatments to induce nepetalactone production and the expression of its related biosynthetic genes in hydroponically grown catnip. Both the 0.5 mM and 1.0 mM SA treatments resulted in upregulation of GPPS and NEPS1. Correlation analysis revealed a low positive co-expression strength between the two genes. However, within the 24-hour time course of the study significant changes in nepetalactone yield were not observed. Chapter 4 expands on the work completed in Chapter 3 by evaluating the effects of SA for a longer time period. Our results did not reveal statistically significant differences in nepetalactone yield between plants treated with SA and untreated plants, but we did observe higher nepetalactone yields in older plants indicating time as a significant source of variation. Also, the relative gene expression of NEPS1 was transiently upregulated during the 1-week time course. This suggests that exogenous treatments can influence the expression of genes in catnip and potentially have downstream effects on the production of its bioactive metabolites. Lastly, Chapter 5 analyzes the global metabolome of Nepeta cataria. This untargeted metabolomics approach uncovers and compares the metabolite profiles of three catnip organs: flowers, leaves, and roots. Multivariate analyses reveal significant differences in metabolite enrichment between the three organs. The enriched metabolic pathways correspond to the specialized ecophysiological functions of each plant organ. Integrating metabolomics data with other omics datasets can improve our mechanistic understanding of catnip biochemistry from the cellular level to the systems-level.