The reliance of phytohormone biosynthesis on primary metabolite precursors

Metabolic pathways regulated by strigolactones foliar spraying enhance osmoregulation and antioxidant defense in drought-prone soybean

BACKGROUND

Drought stress is a significant abiotic stressor that hinders growth, development, and crop yield in soybeans. Strigolactones (SLs) positively regulate plant resistance to drought stress. However, the impact of foliar application of SLs having different concentrations on soybean growth and metabolic pathways related to osmoregulation remains unknown. Therefore, to clarify the impact of SLs on soybean root growth and cellular osmoregulation under drought stress, we initially identified optimal concentrations and assessed key leaf and root indices. Furthermore, we conducted transcriptomic and metabolic analyses to identify differential metabolites and up-regulated genes.

RESULTS

The results demonstrated that drought stress had a significant impact on soybean biomass, root length, root surface area, water content and photosynthetic parameters. However, when SLs were applied through foliar application at appropriate concentrations, the accumulation of ABA and soluble protein increased, which enhanced drought tolerance of soybean seedlings by regulating osmotic balance, protecting membrane integrity, photosynthesis and activating ROS scavenging system. This also led to an increase in soybean root length, lateral root number and root surface area. Furthermore, the effects of different concentrations of SLs on soybean leaves and roots were found to be time-sensitive. However, the application of 0.5 µM SLs had the greatest beneficial impact on soybean growth and root morphogenesis under drought stress. A total of 368 differential metabolites were screened in drought and drought plus SLs treatments. The up-regulated genes were mainly involved in nitrogen compound utilization, and the down-regulated metabolic pathways were mainly involved in maintaining cellular osmoregulation and antioxidant defenses.

CONCLUSIONS

SLs enhance osmoregulation in soybean plants under drought stress by regulating key metabolic pathways including Arachidonic acid metabolism, Glycerophospholipid metabolism, Linoleic acid metabolism, and Flavone and flavonol biosynthesis. This study contributes to the theoretical understanding of improving soybean adaptability and survival in response to drought stress.

Metabolomics and histopathological analysis of two tomato cultivars after co-infection with soil-borne pathogens (Southern root-knot nematode and Fusarium wilt fungus)

Southern root-knot nematode (Meloidogyne incognita) and Fusarium wilt fungus (Fusarium oxysporum) are one of the most predominant pathogens responsible for substantial agricultural yield reduction of tomato. The current study planned to assess the effects of M. incognita (Mi) and F. oxysporum (Fo) and their co-infection on two tomato cultivars, Zhongza 09 (ZZ09) and Gailing Maofen 802 (GLM802). The present study examined the effects of co-infection on leaf morphology, chlorophyll content, leaf area, and histopathology. The present study used metabolomics to evaluate plant-pathogen interactions. The outcomes of the current study revealed that chlorophyll content and leaf area decreased more in GLM802 during co-infection. In co-infection (Fo + Mi), the chlorophyll content reduction in ZZ09 was 11%, while in GLM802 the reduction reached up to 31% as compared to control. Moreover, the reduction in leaf are in ZZ09 was 31%, however, in the GLM802 reduction was observed 54% as compared to control plants. Similarly, GLM802 stems exhibited larger brown patches on their vascular bundles than ZZ09 stems. The rate of browning of GLM802 stems was 247% more than ZZ09, during co-infection. Moreover, GLM802 roots exhibited a higher abundance of hyphae and larger galls than ZZ09 roots. In metabolic studies, glutathione, succinic acid, and 2-isopropylmalic acid decreased, whereas spermine and fumaric acid increased in GLM802 co-infected stems. It indicates that GLM802 is weakly resistant; therefore, F. oxysporum and other pathogens readily damage tissue. In the co-infected stem of ZZ09, L-asparagine and shikimic acid increased, but pipecolic acid, L-saccharine, and 2-isopropylmalic acid declined. L-asparagine was crucial in preserving the stability of nitrogen metabolism, chlorophyll synthesis, and leaf growth in ZZ09. Shikimic acid's substantial accumulation could explain the limited extent of browning observed in the vascular bundles of ZZ09. Thus, the present study provides insight into M. incognita and F. oxysporum co-infection in two tomato cultivars, which may aid breeding efforts to generate commercially viable resistant cultivars. However, further research on the relationship between M. incognita and F. oxysporum in different host plants is required in the future.

Selenium alleviates the adverse effects of microplastics on kale by regulating photosynthesis, redox homeostasis, secondary metabolism and hormones

Kale is a functional food with anti-cancer, antioxidant, and anemia prevention properties. The harmful effects of the emerging pollutant microplastic (MP) on plants have been widely studied, but there is limited research how to mitigate MP damage on plants. Numerous studies have shown that Se is involved in regulating plant resistance to abiotic stresses. The paper investigated impact of MP and Se on kale growth, photosynthesis, reactive oxygen species (ROS) metabolism, phytochemicals, and endogenous hormones. Results revealed that MP triggered a ROS burst, which led to breakdown of antioxidant system in kale, and had significant toxic effects on photosynthetic system, biomass, and accumulation of secondary metabolites, as well as a significant decrease in IAA and a significant increase in GA. Under MP supply, Se mitigated the adverse effects of MP on kale by increasing photosynthetic pigment content, stimulating function of antioxidant system, enhancing secondary metabolite synthesis, and modulating hormonal networks.

Advances in functional studies of plant MYC transcription factors

Myelocytomatosis (MYC) transcription factors (TFs) belong to the basic helix-loop-helix (bHLH) family in plants and play a central role in governing a wide range of physiological processes. These processes encompass plant growth, development, adaptation to biotic and abiotic stresses, as well as secondary metabolism. In recent decades, significant strides have been made in comprehending the multifaceted regulatory functions of MYCs. This advancement has been achieved through the cloning of MYCs and the characterization of plants with MYC deficiencies or overexpression, employing comprehensive genome-wide 'omics' and protein-protein interaction technologies. MYCs act as pivotal components in integrating signals from various phytohormones' transcriptional regulators to orchestrate genome-wide transcriptional reprogramming. In this review, we have compiled current research on the role of MYCs as molecular switches that modulate signal transduction pathways mediated by phytohormones and phytochromes. This comprehensive overview allows us to address lingering questions regarding the interplay of signals in response to environmental cues and developmental shift. It also sheds light on the potential implications for enhancing plant resistance to diverse biotic and abiotic stresses through genetic improvements achieved by plant breeding and synthetic biology efforts.

The immediate metabolomic effects of whole-genome duplication in the greater duckweed, Spirodela polyrhiza

PREMISE

In plants, whole-genome duplication (WGD) is a common mutation with profound evolutionary potential. Given the costs associated with a superfluous genome copy, polyploid establishment is enigmatic. However, in the right environment, immediate phenotypic changes following WGD can facilitate establishment. Metabolite abundances are the direct output of the cell's regulatory network and determine much of the impact of environmental and genetic change on the phenotype. While it is well known that an increase in the bulk amount of genetic material can increase cell size, the impact of gene dosage multiplication on the metabolome remains largely unknown.

METHODS

We used untargeted metabolomics on four genetically distinct diploid-neoautotetraploid pairs of the greater duckweed, Spirodela polyrhiza, to investigate how WGD affects metabolite abundances per cell and per biomass.

RESULTS

Autopolyploidy increased metabolite levels per cell, but the response of individual metabolites varied considerably. However, the impact on metabolite level per biomass was restricted because the increased cell size reduced the metabolite concentration per cell. Nevertheless, we detected both quantitative and qualitative effects of WGD on the metabolome. Many effects were strain-specific, but some were shared by all four strains.

CONCLUSIONS

The nature and impact of metabolic changes after WGD depended strongly on the genotype. Dosage effects have the potential to alter the plant metabolome qualitatively and quantitatively, but were largely balanced out by the reduction in metabolite concentration due to an increase in cell size in this species.

Contrasting defence mechanisms against spider mite infestation in cyanogenic and non-cyanogenic legumes

Understanding the complex interactions between plants and herbivores is essential for improving crop resistance. Aiming to expand the role of cyanogenesis in plant defence, we investigated the response of the cyanogenic Phaseolus lunatus (lima bean) and the non-cyanogenic Phaseolus vulgaris (common bean) to Tetranychus urticae (spider mite) infestation. Despite mite infesting both legumes, leaf damage infringed by this feeder was reduced in lima bean. Comparative transcriptome analyses revealed that both species exhibited substantial metabolic and transcriptional changes upon infestation, although alterations in P. lunatus were significantly more pronounced. Specific differences in amino acid homeostasis and key genes associated with the cyanogenic pathway were observed in these species, as well as the upregulation of the mandelonitrile lyase gene (PlMNL1) following T. urticae feeding. Concomitantly, the PIMNL1 activity increased. Lima bean plants also displayed an induction of β-cyanoalanine synthase (PlCYSC1), a key enzyme for cyanide detoxification, suggesting an internal regulatory mechanism to manage the toxicity of their defence responses. These findings contribute to our understanding of the legume-herbivore interactions and underscore the potential role of cyanogenesis in the elaboration of specific defensive responses, even within the same genus, which may reflect distinctive evolutionary adaptations or varying metabolic capabilities between species.

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.

Silica nanoparticles conferring resistance to bacterial wilt in peanut (Arachis hypogaea L.)

Peanut bacterial wilt (PBW) caused by the pathogen Ralstonia solanacearum severely affects the growth and yield potential of peanut crop. In this study, we synthesized silica nanoparticles (SiO2 NPs), a prospective efficient management approach to control PBW, and conducted a hydroponic experiment to investigate the effects of different SiO2 NPs treatments (i.e., 0, 100, and 500 mg L-1 as NP0, NP100, and NP500, respectively) on promoting plant growth and resistance to R. solanacearum. Results indicated that the disease indices of NP100 and NP500 decreased by 51.5 % and 55.4 % as compared with NP0 under R. solanacearum inoculation, respectively, while the fresh and dry weights and shoot length of NP100 and NP500 increased by 7.62-42.05 %, 9.45-32.06 %, and 2.37-17.83 %, respectively. Furthermore, SiO2 NPs induced an improvement in physio-biochemical enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and lipoxygenase) which eliminated the excess production of hydrogen peroxide, superoxide anions, and malondialdehyde to alleviate PBW stress. Notably, the targeted metabolomic analysis indicated that SiO2 NPs enhanced salicylic acid (SA) contents, which involved the induction of systemic acquired resistance (SAR). Moreover, the transcriptomic analysis revealed that SiO2 NPs modulated the expression of multiple transcription factors (TFs) involved in the hormone pathway, such as AHLs, and the identification of hormone pathways related to plant defense responses, such as the SA pathway, which activated SA-dependent defense mechanisms. Meanwhile, the up-regulated expression of the SA-metabolism gene, salicylate carboxymethyltransferase (SAMT), initiated SAR to promote PBW resistance. Overall, our findings revealed that SiO2 NPs, functioning as a plant elicitor, could effectively modulate physiological enzyme activities and enhance SA contents through the regulation of SA-metabolism genes to confer the PBW resistance in peanuts, which highlighted the potential of SiO2 NPs for sustainable agricultural practices.

Dormancy release of seeds of Podophyllum hexandrum Royle accompanied by changes in phytochemicals and inorganic elements

Podophyllum hexandrum Royle is an alpine medicinal plant of considerable importance, and its seed dormancy severely inhibits population renewal. Although cold stratification can break dormancy to a certain extent, the migration and accumulation of phytochemicals and inorganic elements in the seeds during dormancy release and their functions remain unclear. Changes in phytochemicals and inorganic elements in different seed parts were analyzed during dormancy. The key differential phytochemicals and inorganic elements were screened and their association with dormancy release and their roles in dormancy release were explored. The results showed that dormancy release may have occurred following the decrease in palmitic acid and linoleic acid content in the seeds and the increase in 2,3-dihydro-3,5-dihydro-6-methyl-4 (h)-pyran-4-one content in the endosperm. Meanwhile, 6-propyltridecane and hexadecane in the seed coat may enhance the water permeability of seeds to speed up germination. Mg may migrate from the seed coat to the endosperm and seed embryos, whereas Co may migrate from the seed embryo to the seed coat. Ca, Mn, Mg, and Co are involved in various physiological metabolic processes, which may facilitate the dormancy release of P. hexandrum seeds. These findings have enhanced our understanding of the mechanisms of dormancy release in P. hexandrum seeds and can serve as a reference for the development of more effective dormancy-breaking techniques for the conservation of this endangered medicinal plant.

Physiological and omics-based insights for underpinning the molecular regulation of secondary metabolite production in medicinal plants: UV stress resilience

Despite complex phytoconstituents, the commercial potential of medicinal plants under ultraviolet (UV) stress environment hasn't been fully comprehended. Due to sessile nature, these plants are constantly exposed to damaging radiation, which disturbs their natural physiological and biochemical processes. To combat with UV stress, plants synthesized several small organic molecules (natural products of low molecular mass like alkaloids, terpenoids, flavonoids and phenolics, etc.) known as plant secondary metabolites (PSMs) that come into play to counteract the adverse effect of stress. Plants adapted a stress response by organizing the expression of several genes, enzymes, transcription factors, and proteins involved in the synthesis of chemical substances and by making the signaling cascade (a series of chemical reactions induced by a stimulus within a biological cell) flexible to boost the defensive response. To neutralize UV exposure, secondary metabolites and their signaling network regulate cellular processes at the molecular level. Conventional breeding methods are time-consuming and difficult to reveal the molecular pattern of the stress tolerance medicinal plants. Acquiring in-depth knowledge of the molecular drivers behind the defensive mechanism of medicinal plants against UV radiation would yield advantages (economical and biological) that will bring prosperity to the burgeoning world's population. Thus, this review article emphasized the comprehensive information and clues to identify several potential genes, transcription factors (TFs), proteins, biosynthetic pathways, and biological networks which are involved in resilience mechanism under UV stress in medicinal plants of high-altitudes.

Can plant hormonomics be built on simple analysis? A review

The field of plant hormonomics focuses on the qualitative and quantitative analysis of the hormone complement in plant samples, akin to other omics sciences. Plant hormones, alongside primary and secondary metabolites, govern vital processes throughout a plant's lifecycle. While active hormones have received significant attention, studying all related compounds provides valuable insights into internal processes. Conventional single-class plant hormone analysis employs thorough sample purification, short analysis and triple quadrupole tandem mass spectrometry. Conversely, comprehensive hormonomics analysis necessitates minimal purification, robust and efficient separation and better-performing mass spectrometry instruments. This review summarizes the current status of plant hormone analysis methods, focusing on sample preparation, advances in chromatographic separation and mass spectrometric detection, including a discussion on internal standard selection and the potential of derivatization. Moreover, current approaches for assessing the spatiotemporal distribution are evaluated. The review touches on the legitimacy of the term plant hormonomics by exploring the current status of methods and outlining possible future trends.

A comprehensive view of metabolic responses to CYP98 perturbation in ancestral plants

Cytochrome P450 monooxygenase 98 (CYP98) is a critical rate-limiting enzyme of the phenylpropanoid pathway. One of the end-product of the phenylpropanoid pathway is a lignin monomer, although the occurrence of lignin in bryophytes is controversial. Here we investigated the functions of PpCYP98 in Physcomitrium patens by transcriptome and metabolome analyses. We identified 5266 differentially expressed genes (DEGs) and 68 differentially abundant secondary metabolites between wild-type and ΔPpCYP98 gametophores. Of the identified metabolites, 23 phenolic acids were identified, with only one showing upregulation. Among the phenolic acids, 4-coumaroyl tartaric acid and chlorogenic acid showed significant decreases. Declines were also observed in coniferylaldehyde and coniferin, precursor substances and downstream products of the lignin monomer coniferyl alcohol, respectively. Thus, the pre-lignin synthesis pathway already exists in bryophytes, and PpCYP98 plays vital roles in this pathway. Besides, most flavonoids show significant reductions, including eriodyctiol, dihydroquecetin, and dihydromyricetin, whereas naringenin chalone and dihydrokaempferol were increased after PpCYP98 knockout. Therefore, the synthesis of flavonoids shares the core pathway with phenylpropanoids and mainly starts from caffeoyl-CoA, that is the compound of divergence between the two pathways in moss. PpCYP98 showed systemic effects on metabolisms, including carbohydrate, fatty acid, and hormonal signaling transductions, suggesting that PpCYP98 might indirectly regulate carbon influx allocation. Our results demonstrated roles of PpCYP98 were essential for the development of the early landing plant.

Carotenoids Occurring in Maize Affect the Redox Homeostasis of Fusarium graminearum and Its Production of Type B Trichothecene Mycotoxins: New Insights Supporting Their Role in Maize Resistance to Giberella Ear Rot

Fusarium graminearum is the causal agent of Gibberella ear rot (GER) in maize, a devastating fungal disease resulting in yield reduction and contamination of grains with type B trichothecene (TCTB) mycotoxins. Reducing GER damage requires the implementation of an integrated management strategy in which the use of resistant maize genotypes is a key factor. The present study aimed at providing new phenotyping tools to improve breeding pipelines by investigating the yet understudied contribution of carotenoids to GER resistance. Here, we demonstrated for the first time the efficiency of carotenoid extracts from various maize genotypes to inhibit the production of TCTB by F. graminearum. We further suggested that zeaxanthin could be a key actor of this inhibition efficiency, notably via a negative transcriptional control of several biosynthetic genes of the TCTB pathway. Besides, we demonstrated that zeaxanthin treatments led to profound perturbations in the fungal redox homeostasis by affecting the expression of key genes encoding ROS detoxifying enzymes, several of them being involved in F. graminearum virulence during plant infection. Altogether, our data support the contribution of carotenoids to the mechanisms employed by maize to counteract F. graminearum infection and its production of TCTB.

Dendrophthoe falcata (L.f.) Ettingsh. and Dendrophthoe pentandra (L.) Miq.: A review of traditional medical uses, phytochemistry, pharmacology, toxicity, and applications

Dendrophthoe falcata (L.f.) Ettingsh. (DF) and Dendrophthoe pentandra (L.) Miq. (DP) have been traditionally used for the treatment of various ailments, such as cancer, ulcers, asthma, paralysis, skin diseases, tuberculosis, and menstrual troubles, in the ethnomedicinal systems of India and Indonesia. Currently, the chemical structures of 46 compounds have been elucidated from DF and DP, including flavonoids, triterpenes, tannins, steroids, open-chain aliphatics, benzyl derivates, and cyclic chain derivatives. In vitro assays have revealed their anti-tumor and anti-microbial activities. In vivo studies have unraveled their pharmacological properties against tumors, depression, fertility disorders, inflammatory responses, and so on. Additionally, their weak toxicity to rats and brine shrimp, as well as their promising applications for pharmaceutical preparations and combined medication, were also revealed. Herein, we not only recapitulated traditional medical uses, phytochemistry, pharmacology, toxicity, and applications of DF and DP but also discussed current research limitations and future perspectives, which are instructive for those interested in them and are committed to advancing parasitic plants to the Frontier of phytomedicine. We highlighted that DF and DP will become promising medical plants rather than being discarded as notorious pests, provided that more and deeper research is undertaken.

Role of Promising Secondary Metabolites to Confer Resistance Against Environmental Stresses in Crop Plants: Current Scenario and Future Perspectives

Plants often face incompatible growing environments like drought, salinity, cold, frost, and elevated temperatures that affect plant growth and development leading to low yield and, in worse circumstances, plant death. The arsenal of versatile compounds for plant consumption and structure is called metabolites, which allows them to develop strategies to stop enemies, fight pathogens, replace their competitors and go beyond environmental restraints. These elements are formed under particular abiotic stresses like flooding, heat, drought, cold, etc., and biotic stress such as a pathogenic attack, thus associated with survival strategy of plants. Stress responses of plants are vigorous and include multifaceted crosstalk between different levels of regulation, including regulation of metabolism and expression of genes for morphological and physiological adaptation. To date, many of these compounds and their biosynthetic pathways have been found in the plant kingdom. Metabolites like amino acids, phenolics, hormones, polyamines, compatible solutes, antioxidants, pathogen related proteins (PR proteins), etc. are crucial for growth, stress tolerance, and plant defense. This review focuses on promising metabolites involved in stress tolerance under severe conditions and events signaling the mediation of stress-induced metabolic changes are presented.