Wound-response jasmonate dynamics in the primary vasculature

Laser-wound stimulated adventitious root formation of Rosa canina cuttings involves a complex response at plant hormonal and metabolic level

Introduction

The presence of wounds in addition to the excision-induced wounds after severance from the stock plants is known to positively influence adventitious root formation of woody plant cuttings. Previous morphological studies highlighted laser wounding as a technique allowing to precisely control the decisive ablation depth. However, the biochemical processes involved in the response of rooting to the additional wounding remained unexplored.

Methods

The present study analyzed changes in the plant hormone and carbohydrate profiles in response to laser treatments of rose leafy single-node stem cuttings (Rosa canina 'Pfänder'). Concentrations of four groups of plant hormones and of carbohydrates were monitored in three different stem sections of the cutting base during the first eight days after excision of cuttings. In addition, histology was employed to investigate anatomical changes at the basal wound and the laser wounds at the start and the end of the experiment after 40 days.

Results

Laser ablation caused an increase of vascular tissue dimension directly in the laser wound, and increased the quantity and quality of rooting compared to control cuttings. A clear early local rise of jasmonic acid (JA) was detected directly in wounded areas after laser marking, as well as an increase in abscisic acid (ABA) that persisted for the subsequent days. Indole-3-acetic acid (IAA) levels were relatively high on day zero, but decreased thereafter. Interestingly, higher IAA levels were maintained in the stem section below the axillary bud compared with the opposite section. Laser-treated cuttings presented a clear increase in contents of IAA-amino acid conjugates (IAAGlu and IAAsp) and the oxidation product OxIAA. Differences in concentration of these IAA metabolites were related to the position of the laser wound relative to the axillary bud and leaf. Additionally, laser treatments caused gradually increased levels of the cytokinin N6-isopentenyladenine (iP) in laser-treated zones, and of zeatin riboside specifically when the laser wound was placed on the leaf-bud side. Additional laser wounding reduced starch and sucrose levels in all wounded sections at the end of the evaluation period, independently of the wounding location.

Discussion

The results of this study indicate that presence of additional injured tissue triggers a complex biochemical adjustment at the base of the cutting responsible of inducing vascular tissue growth and capable of generating a positive response to adventitious root formation.

Identification of "modified OPDA (mo-OPDA)" as a Michael adduct of cis-OPDA

cis-(+)-12-Oxo-phytodienoic acid (cis-OPDA) is a significant plant oxylipin, known as a biosynthetic precursor of the plant hormone jasmonoyl-l-isoleucine (JA-Ile), and a bioactive substance in plant environmental stresses. A recent study showed that a plant dioxygenase, Jasmonate Induced Dioxygenase 1 (JID1), converts cis-OPDA into an unidentified metabolite termed "modified-OPDA (mo-OPDA)" in Arabidopsis thaliana. Here, using ultra-performance liquid chromatography coupled with triple quad mass spectrometry (UPLC-MS/MS) experiment, the chemical identity of "mo-OPDA" was demonstrated and identified as a conjugate between cis-OPDA and 2-mercaptoethanol (cis-OPDA-2ME), an artifact produced by Michael addition during the JID1 digestion of cis-OPDA. However, previous reports demonstrated a decreased accumulation of cis-OPDA in the JID1-OE line, suggesting the existence of an unknown JID1-mediated mechanism regulating the level of cis-OPDA in A. thaliana.

ROS are universal cell-to-cell stress signals

The interplay between reactive oxygen species (ROS) and the redox state of cells is deeply rooted in the biology of almost all organisms, regulating development, growth, and responses to the environment. Recent studies revealed that the ROS levels and redox state of one cell can be transmitted, as an information 'state' or 'currency', to other cells and spread by cell-to-cell communication within an entire community of cells or an organism. Here, we discuss the different pathways that mediate cell-to-cell signaling in plants, their hierarchy, and the different mechanisms that transmit ROS/redox signaling between different cells. We further hypothesize that ROS/redox signaling between different organisms could play a key role within the 'one world' principle, impacting human health and our future.

Revisiting plant electric signaling: Challenging an old phenomenon with novel discoveries

Higher plants efficiently orchestrate rapid systemic responses to diverse environmental stimuli through electric signaling. This review explores the mechanisms underlying two main types of electric signals in plants, action potentials (APs) and slow wave potentials (SWPs), and how new discoveries challenge conventional neurophysiological paradigms traditionally forming their theoretical foundations. Animal APs are biophysically well-defined, whereas plant APs are often classified based on their shape, lacking thorough characterization. SWPs are depolarizing electric signals deviating from this shape, leading to an oversimplified classification of plant electric signals. Indeed, investigating the generation and propagation of plant APs and SWPs showcases a complex interplay of mechanisms that sustain self-propagating signals and internally propagating stimuli, resulting in membrane depolarization, cytosolic calcium increase, and alterations in reactive oxygen species and pH. A holistic understanding of plant electric signaling will rely on unraveling the network of ion-conducting proteins, signaling molecules, and mechanisms for signal generation and propagation.

Phospholipid Signaling in Crop Plants: A Field to Explore

In plant models such as Arabidopsis thaliana, phosphatidic acid (PA), a key molecule of lipid signaling, was shown not only to be involved in stress responses, but also in plant development and nutrition. In this article, we highlight lipid signaling existing in crop species. Based on open access databases, we update the list of sequences encoding phospholipases D, phosphoinositide-dependent phospholipases C, and diacylglycerol-kinases, enzymes that lead to the production of PA. We show that structural features of these enzymes from model plants are conserved in equivalent proteins from selected crop species. We then present an in-depth discussion of the structural characteristics of these proteins before focusing on PA binding proteins. For the purpose of this article, we consider RESPIRATORY BURST OXIDASE HOMOLOGUEs (RBOHs), the most documented PA target proteins. Finally, we present pioneering experiments that show, by different approaches such as monitoring of gene expression, use of pharmacological agents, ectopic over-expression of genes, and the creation of silenced mutants, that lipid signaling plays major roles in crop species. Finally, we present major open questions that require attention since we have only a perception of the peak of the iceberg when it comes to the exciting field of phospholipid signaling in plants.

Isolation and Structure Determination of cis-OPDA-α-Monoglyceride from Arabidopsis thaliana

cis-12-oxo-Phytodieneoic acid-α-monoglyceride (1) was isolated from Arabidopsis thaliana. The chemical structure of 1 was elucidated based on exhaustive 1D and 2D NMR spectroscopic measurements and supported by FDMS and HRFDMS data. The absolute configuration of the cis-OPDA moiety in 1 was determined by comparison of 1H NMR spectra and ECD measurements. With respect to the absolute configuration of the β-position of the glycerol backbone, the 2:3 ratio of (S) to (R) was determined by making ester-bonded derivatives with (R)-(+)-α-methoxy-α-trifluoromethylphenylacetyl chloride and comparing 1H NMR spectra. Wounding stress did not increase endogenous levels of 1, and it was revealed 1 had an inhibitory effect of A. thaliana post germination growth. Notably, the endogenous amount of 1 was higher than the amounts of (+)-7-iso-jasmonic acid and (+)-cis-OPDA in intact plants. 1 also showed antimicrobial activity against Gram-positive bacteria, but jasmonic acid did not. It was also found that α-linolenic acid-α-monoglyceride was converted into 1 in the A. thaliana plant, which implied α-linolenic acid-α-monoglyceride was a biosynthetic intermediate of 1.

Advanced high-resolution chromatographic strategies for efficient isolation of natural products from complex biological matrices: from metabolite profiling to pure chemical entities

The isolation of pure compounds from extracts represents a key step common to all investigations of natural product (NP) research. Isolation methods have gone through a remarkable evolution. Current approaches combine powerful metabolite profiling methods for compounds annotation with omics mining results and/or bioassay for bioactive NPs/biomarkers priorisation. Targeted isolation of prioritized NPs is performed using high-resolution chromatographic methods that closely match those used for analytical profiling. Considerable progress has been made by the introduction of innovative stationary phases providing remarkable selectivity for efficient NPs isolation. Today, efficient separation conditions determined at the analytical scale using high- or ultra-high-performance liquid chromatography can be optimized via HPLC modelling software and efficiently transferred to the semi-preparative scale by chromatographic calculation. This ensures similar selectivity at both the analytical and preparative scales and provides a precise separation prediction. High-resolution conditions at the preparative scale can notably be granted using optimized sample preparation and dry load sample introduction. Monitoring by ultraviolet, mass spectrometry, and or universal systems such as evaporative light scattering detectors and nuclear magnetic resonance allows to precisely guide the isolation or trigger the collection of specific NPs with different structural scaffolds. Such approaches can be applied at different scales depending on the amounts of NPs to be isolated. This review will showcase recent research to highlight both the potential and constraints of using these cutting-edge technologies for the isolation of plant and microorganism metabolites. Several strategies involving their application will be examined and critically discussed.

Graphical abstract

pH change accompanying long-distance electrical signal controls systemic jasmonate biosynthesis

Local damaging stimuli cause a rapid increase in the content of the defense phytohormone jasmonic acid (JA) and its biologically active derivative jasmonoyl-L-isoleucine (JA-Ile) in undamaged distal tissues. The increase in JA and JA-Ile levels was coincident with a rapid decrease in the levels of the precursor 12-oxo-phytodienoic acid (OPDA). The propagation of a stimulus-induced long-distance electrical signal, variation potential (VP), which is accompanied by intracellular changes in pH and Ca2+ levels, preceded systemic changes in jasmonate content. The decrease in pH during VP, mediated by transient inactivation of the plasma membrane H+-ATPase, induced the conversion of OPDA to JA, probably by regulating the availability of the OPDA substrate to JA biosynthetic enzymes. The regulation of systemic synthesis of JA and JA-Ile by the Ca2+ wave accompanying VP most likely occurs by the same mechanism of pH-induced conversion of OPDA to JA due to Ca2+-mediated decrease in pH as a result of H+-ATPase inactivation. Thus, the transient increase in intracellular Ca2+ levels and the transient decrease in intracellular pH are most likely the key mechanisms of VP-mediated regulation of jasmonate production in systemic tissues upon local stimulation.

Phytohormones in a universe of regulatory metabolites: lessons from jasmonate

Small-molecule phytohormones exert control over plant growth, development, and stress responses by coordinating the patterns of gene expression within and between cells. Increasing evidence indicates that currently recognized plant hormones are part of a larger group of regulatory metabolites that have acquired signaling properties during the evolution of land plants. This rich assortment of chemical signals reflects the tremendous diversity of plant secondary metabolism, which offers evolutionary solutions to the daunting challenges of sessility and other unique aspects of plant biology. A major gap in our current understanding of plant regulatory metabolites is the lack of insight into the direct targets of these compounds. Here, we illustrate the blurred distinction between classical phytohormones and other bioactive metabolites by highlighting the major scientific advances that transformed the view of jasmonate from an interesting floral scent to a potent transcriptional regulator. Lessons from jasmonate research generally apply to other phytohormones and thus may help provide a broad understanding of regulatory metabolite-protein interactions. In providing a framework that links small-molecule diversity to transcriptional plasticity, we hope to stimulate future research to explore the evolution, functions, and mechanisms of perception of a broad range of plant regulatory metabolites.

Identification and characterization of GLYCEROLIPASE A1 for wound-triggered JA biosynthesis in Nicotiana benthamiana leaves

Although many important discoveries have been made regarding the jasmonate signaling pathway, how jasmonate biosynthesis is initiated is still a major unanswered question in the field. Previous evidences suggest that jasmonate biosynthesis is limited by the availability of fatty acid precursor, such as ⍺-linolenic acid (⍺-LA). This indicates that the lipase responsible for releasing α-LA in the chloroplast, where early steps of jasmonate biosynthesis take place, is the key initial step in the jasmonate biosynthetic pathway. Nicotiana benthamiana glycerol lipase A1 (NbGLA1) is homologous to N. attenuata GLA1 (NaGLA1) which has been reported to be a major lipase in leaves for jasmonate biosynthesis. NbGLA1 was studied for its potential usefulness in a species that is more common in laboratories. Virus-induced gene silencing of both NbGLA1 and NbGLA2, another homolog, resulted in more than 80% reduction in jasmonic acid (JA) biosynthesis in wounded leaves. Overexpression of NbGLA1 utilizing an inducible vector system failed to increase JA, indicating that transcriptional induction of NbGLA1 is insufficient to trigger JA biosynthesis. However, co-treatment with wounding in addition to NbGLA1 induction increased JA accumulation several fold higher than the gene expression or wounding alone, indicating an enhancement of the enzyme activity by wounding. Domain-deletion of a 126-bp C-terminal region hypothesized to have regulatory roles increased NbGLA1-induced JA level. Together, the data show NbGLA1 to be a major lipase for wound-induced JA biosynthesis in N. benthamiana leaves and demonstrate the use of inducible promoter-driven construct of NbGLA1 in conjunction with its transient expression in N. benthamiana as a useful system to study its protein function.