Lucio D’andrea

Background: Specialised anti-herbivory metabolites are abundant in the solanaceous genus Nicotiana. These metabolites include the large family of 17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs). Many HGL-DTGs occur exclusively within the Nicotiana genus, but information from the molecular model species N. tabacum, N. benthamiana, and the tree tobacco N. glauca is limited. Objectives: We studied HGL-DTG occurrence and complexity in these species with the aim of providing in-depth reference annotations and comprehensive HGL-DTG inventories. Methods: We analysed polar metabolite extracts in comparison to the previously investigated wild reference species N. attenuata using positive ESI(+) and negative ESI(-) mode electrospray ionisation LC-MS and MS/MS. Results: We provide annotations of 66 HGL-DTGs with in-source and MS/MS fragmentation spectra for selected HGL-DTGs with exemplary fragment interpretations of ESI(+) as well as less studied ESI(-) spectra. We assemble a potential biosynthesis pathway comparing the presence of HGL-DTGs in N. tabacum, N. glauca, and N. benthamiana to N. attenuata. Approximately one-third of HGL-DTGs are chromatographically resolved isomers of hexose, deoxyhexose, or malonate conjugates. The number of isomers is especially high for conjugates with low numbers of deoxyhexose moieties. Conclusions: We extend the number of known HGL-DTGs with a focus on Nicotiana model species and demonstrate that the HGL-DTG family of N. tabacum plants can be surprisingly complex. Our study provides an improved basis with detailed references to previous studies of wild Nicotiana species and enables inference of HGL-DTG pathways with required enzymes for the biosynthesis of this important family of specialised defence metabolites.

Summary: MetPlast, is an R package that provides the functionalities necessary to analyze biological samples’ metabolic plasticity. This package takes advantage of the statistical framework provided by the Information Theory to quantify and defined metabolic plasticity parameters. Using previous implemented formula based on Shannon entropy we automatize the calculation and visualization of a set of metabolic plasticity indexes including metabolic diversity, metabolome specialization, and metabolite specialization. We use a publicly available metabolic data set on tomato domestication to demonstrate the power of the present tool to evaluate changes in metabolic plasticity parameters. Thus, MetPlast represents a new and invaluable member of the computational metabolomics toolbox, that will certainly help scientists to unveil hidden information in cell metabolomic landscape. Availability and implementation: Freely available at https://github.com/danlucio86/MetPlast

Plastids, the defining organelles of plant cells, undergo physiological and morphological changes to fulfill distinct biological functions. In particular, the differentiation of chloroplasts into chromoplasts results in an enhanced storage capacity for carotenoids with industrial and nutritional value such as beta-carotene (pro-vitamin A). Here, we show that synthetically inducing a burst in the production of phytoene, the first committed intermediate of the carotenoid pathway, elicits an artificial chloroplast-to-chromoplast differentiation in leaves. Phytoene overproduction initially interferes with photosynthesis, acting as a metabolic threshold switch mechanism that weakens chloroplast identity. In a second stage, phytoene conversion into downstream carotenoids is required for the differentiation of chromoplasts. Our findings reveal that lowering the photosynthetic capacity of chloroplasts and increasing the production of carotenoids are not just the consequence but an absolute requirement for chromoplast differentiation, which additionally involves a concurrent reprogramming of nuclear gene expression and plastid morphology for improved carotenoid storage.