Plant Science

Metabolite modifications play a critical role in enhancing plants’ adaptability to environmental changes and serve as a major source of functional diversity in metabolites. However, current metabolomics approaches are limited to targeted analyses of a small number of known modified metabolites and lack comprehensive, large-scale studies of plant metabolite modifications. Here, we describe a widely targeted metabolite modificomics (WTMM) strategy, developed using ultra-high-performance liquid chromatography–quadrupole linear ion trap (UHPLC-Q-Trap) and ultra-high-performance liquid chromatography–Q-Exactive Orbitrap (UHPLC-QE-Orbitrap) technologies. This strategy enables high-throughput identification and sensitive quantification of modified metabolites. Using tomato as a model, we conducted a metabolite modificomics study and constructed a WTMM database, identifying 165 novel modified metabolites. The WTMM strategy is broadly applicable and can be extended to the study of other plant species.

Arbuscular mycorrhizal (AM) fungi engage in symbiotic relationships with plants, influencing their phosphate (Pi) uptake pathways, metabolism, and root cell physiology. Despite the significant role of Pi, its distribution and response dynamics in mycorrhizal roots remain largely unexplored. While traditional techniques for Pi measurement have shed some light on this, real-time cellular-level monitoring has been a challenge. With the evolution of quantitative imaging with confocal microscopy, particularly the use of genetically encoded fluorescent sensors, live imaging of intracellular Pi concentrations is now achievable. Among these sensors, fluorescence resonance energy transfer (FRET)-based biosensors stand out for their accuracy. In this study, we employ the Pi-specific biosensor (cpFLIPPi-5.3m) targeted to the cytosol or plastids of Brachypodium distachyon plants, enabling us to monitor intracellular Pi dynamics during AM symbiosis. A complementary control sensor, cpFLIPPi-Null, is introduced to monitor non-Pi-specific changes. Leveraging a semi-automated ImageJ macro for sensitized FRET analysis, this method provides a precise and efficient way to determine relative intracellular Pi levels at the level of individual cells or organelles.

The flux in photosynthesis can be studied by performing ¹³CO₂ pulse labelling and analysing the temporal labelling kinetics of metabolic intermediates using gas or liquid chromatography linked to mass spectrometry. Metabolic flux analysis (MFA) is the primary approach for analysing metabolic network function and quantifying intracellular metabolic fluxes. Different MFA approaches differ based on the metabolic state (steady vs. non-steady state) and the use of stable isotope tracers. The main methodology used to investigate metabolic systems is metabolite steady state associated with stable isotope labelling experiments. Specifically, in biological systems like photoautotrophic organisms, isotopic non-stationary ¹³C metabolic flux analysis at metabolic steady state with transient isotopic labelling (¹³C-INST-MFA) is required. The common requirement for metabolic steady state, alongside its very short half-timed reactions, complicates robust MFA of photosynthetic metabolism. While custom gas chambers design has addressed these challenges in various model plants, no similar tools were developed for liquid photosynthetic cultures (e.g., algae, cyanobacteria), where diffusion and equilibration of inorganic carbon species in the medium entails a new dimension of complexity. Recently, a novel tailor-made microfluidics labelling system has been introduced, supplying short ¹³CO₂ pulses at steady state, and resolving fluxes across most photosynthetic metabolic pathways in algae. The system involves injecting algal cultures and medium containing pre-equilibrated inorganic ¹³C into a microfluidic mixer, followed by rapid metabolic quenching, enabling precise seconds-level label pulses. This was complemented by a ¹³CO₂-bubbling-based open labelling system (photobioreactor), allowing long pulses (minutes–hours) required for investigating fluxes into central C metabolism and major products. This combined labelling procedure provides a comprehensive fluxome cover for most algal photosynthetic and central C metabolism pathways, thus allowing comparative flux analyses across algae and plants.

The sesquiterpene lactone compound artemisinin is a natural medicinal product of commercial importance. This Artemisia annua–derived secondary metabolite is well known for its antimalarial activity and has been studied in several other biological assays. However, the major shortcoming in its production and commercialization is its low accumulation in the native plant. Moreover, the chemical synthesis of artemisinin is difficult and expensive due to its complex structure. Hence, an alternative and sustainable production system of artemisinin in a heterologous host is required. Previously, heterologous production of artemisinin was achieved by Agrobacterium-mediated transformation. However, this requires extensive bioengineering of modified Nicotiana plants. Recently, a technique involving direct in vivo assembly of multiple DNA fragments in the moss, P. patens, has been successfully established. We utilized this technique to engineer artemisinin biosynthetic pathway genes into the moss, and artemisinin was obtained without further modifications with high initial production. Here, we provide protocols for establishing moss culture accumulating artemisinin, including culture preparation, transformation method, and compound detection via HS-SPME, UPLC-MRM-MS, and LC-QTOF-MS. The bioengineering of moss opens up a more sustainable, cost effective, and scalable platform not only in artemisinin production but also other high-value specialized metabolites in the future.

Aphids are a serious pest of crops across the world. Aphids feed by inserting their flexible hypodermal needlelike mouthparts, or stylets, into their host plant tissues. They navigate their way to the phloem where they feed on its sap causing little mechanical damage to the plant. Additionally, while feeding, aphids secrete proteinaceous effectors in their saliva to alter plant metabolism and disrupt plant defenses to gain an advantage over the plant. Even with these arsenals to overcome plant responses, plants have evolved ways to detect and counter with defense responses to curtail aphid infestation. One of such response of cowpea to cowpea aphid infestation, is accumulation of the metabolite methylglyoxal. Methylglyoxal is an α,β-dicarbonyl ketoaldehyde that is toxic at high concentrations. Methylglyoxal levels increase modestly after exposure to a number of different abiotic and biotic stresses and has been shown to act as an emerging defense signaling molecule at low levels. Here we describe a protocol to measure methylglyoxal in cowpea leaves after cowpea aphid infestation, by utilizing a perchloric acid extraction process. The extracted supernatant was neutralized with potassium carbonate, and methylglyoxal was quantified through its reaction with N-acetyl-L-cysteine to form N-α-acetyl-S-(1-hydroxy-2-oxo-prop-1-yl)cysteine, a product that is quantified spectrophotometrically.

In this protocol, we describe how to quantify starch in guard cells of Arabidopsis thaliana using the fluorophore propidium iodide and confocal laser scanning microscopy. This simple method enables monitoring, with unprecedented resolution, the dynamics of starch in guard cells.

Plant vacuoles are the largest compartment in plant cells, occupying more than 80% of the cell volume. A variety of proteins, sugars, pigments and other metabolites are stored in these organelles (Paris et al., 1996; Olbrich et al., 2007). Flowers produce a variety of specialized metabolites, some of which are unique to this organ, such as components of pollination syndromes, i.e., scent volatiles and flavonoids (Hoballah et al., 2007; Cna'ani et al., 2015). To study the compounds stored in floral vacuoles, this compartment must be separated from the rest of the cell. To enable isolation of vacuoles, protoplasts were first generated by incubating pierced corollas with cellulase and macrozyme enzymes. After filtering and several centrifugation steps, protoplasts were separated from the debris and damaged/burst protoplasts, as revealed by microscopic observation. Concentrated protoplasts were lysed, and vacuoles were extracted by Ficoll-gradient centrifugation. Vacuoles were used for quantitative GC-MS analyses of sequestered metabolites. This method allowed us to identify vacuoles as the subcellular accumulation site of glycosylated volatile phenylpropanoids and to hypothesize that conjugated scent compounds are sequestered in the vacuoles en route to the headspace (Cna'ani et al., 2017).

This protocol delivers a method to determine the biosynthetic capability of comfrey leaves for pyrrolizidine alkaloids independently from other organs like roots or flowers.

The protocol applies and combines radioactive tracer experiments with standard and modern techniques like thin layer chromatography (TLC), solid-phase extraction (SPE), high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS).

1-MCP (1-methylcyclopropene) is a simple synthetic hydrocarbon molecule that interacts with the ethylene receptor and inhibits the response of fruit or plant to ethylene. 1-MCP has opened new opportunities in handling harvested crops and serves as a powerful tool to learn about plant response to ethylene (Watkins and Miller, 2006). 1-MCP is manufactured by Agrofresh and known by its commercial name Smartfresh^SM.

Plants use nitrate, nitrite, and ammonium as inorganic nitrogen (N) sources. These N compounds are included in plant tissues at various concentrations depending on the balance between their uptake and assimilation. Thus, the contents of nitrate, nitrite, and ammonium are physiological indicators of plant N economy. Here, we describe a protocol for measurement of these inorganic N species in A. thaliana shoots or roots.