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KAI2 receptors, classified as plant α/β hydrolase enzymes, are capable of perceiving smoke-derived butenolide signals and endogenous yet unidentified KAI2-ligands (KLs). While the number of functional KAI2 receptors varies among land plant species, rice has only one KAI2 gene. Rice, a significant crop and representative of grasses, relies on KAI2-mediated Arbuscular mycorrhiza (AM) symbioses to flourish in traditionally arid and nutrient-poor environments. This study presents the first crystal structure of an active rice (Oryza sativa, Os) KAI2 hydrolase receptor. Our structural and biochemical analyses uncover grass-unique pocket residues influencing ligand sensitivity and hydrolytic activity. Through structure-guided analysis, we identify a specific residue whose mutation enables the increase or decrease of ligand perception, catalytic activity, and signal transduction. Furthermore, we investigate OsKAI2-mediated signaling by examining its ability to form a complex with its binding partner, the F-box protein DWARF3 (D3) ubiquitin ligase and subsequent degradation of the target substrate OsSMAX1, demonstrating the significant role of hydrophobic interactions in the OsKAI2-D3 interface. This study provides new insights into the diverse and pivotal roles of the OsKAI2 signaling pathway in the plant kingdom, particularly in grasses.

The arbuscular mycorrhizal (AM) symbiosis formed by most extant land plants with symbiotic fungi evolved 450 Ma. AM promotes plant growth by improving mineral nutrient and water uptake, while the symbiotic fungi obtain carbon in return. A number of plant genes regulating the steps leading to an efficient symbiosis have been identified; however, our understanding of the metabolic processes involved in the symbiosis and how they were wired to symbiosis regulation during plant evolution remains limited. Among them, the exchange of chemical signals, the activation of dedicated biosynthesis pathways and the production of secondary metabolites regulating late stages of the AM symbiosis begin to be well described across several land plant clades. Here, we review our current understanding of these processes and propose future directions to fully grasp the phylogenetic distribution and role played by small molecules during this ancient plant symbiosis. This article is part of the theme issue 'The evolution of plant metabolism'. [ABSTRACT FROM AUTHOR]

Summary: The phytohormone strigolactone (SL) inhibits shoot branching, whereas the signalling metabolite trehalose 6‐phosphate (Tre6P) promotes branching. How Tre6P and SL signalling may interact and which molecular mechanisms might be involved remains largely unknown.Transcript profiling of Arabidopsis SL mutants revealed a cluster of differentially expressed genes highly enriched in the Tre6P pathway compared with wild‐type (WT) plants or brc1 mutants. Tre6P‐related genes were also differentially expressed in axillary buds of garden pea (Pisum sativum) SL mutants.Tre6P levels were elevated in the SL signalling mutant more axillary (max) growth 2 compared with other SL mutants or WT plants indicating a role of MAX2‐dependent SL signalling in regulating Tre6P levels.A transgenic approach to increase Tre6P levels demonstrated that all SL mutant lines and brc1 flowered earlier, showing all of these mutants were responsive to Tre6P. Elevated Tre6P led to increased branching in WT plants but not in max2 and max4 mutants, indicating some dependency between the SL pathway and Tre6P regulation of shoot branching. By contrast, elevated Tre6P led to an enhanced branching phenotype in brc1 mutants indicating independence between BRC1 and Tre6P. A model is proposed whereby SL signalling represses branching via Tre6P and independently of the BRC1 pathway. [ABSTRACT FROM AUTHOR]

Inter-kingdom communication through small molecules is essential to the coexistence of organisms in an ecosystem. In soil communities, the plant root is a nexus of interactions for a remarkable number of fungi and is a source of small-molecule plant hormones that shape fungal compositions. Although hormone signaling pathways are established in plants, how fungi perceive and respond to molecules is unclear because many plant-associated fungi are recalcitrant to experimentation. Here, we develop an approach using the model fungus, Saccharomyces cerevisiae , to elucidate mechanisms of fungal response to plant hormones. Two plant hormones, strigolactone and methyl jasmonate, produce unique transcript profiles in yeast, affecting phosphate and sugar metabolism, respectively. Genetic analysis in combination with structural studies suggests that SLs require the high-affinity transporter Pho84 to modulate phosphate homeostasis. The ability to study small-molecule plant hormones in a tractable genetic system should have utility in understanding fungal-plant interactions. [Display omitted] • The plant hormone strigolactone hijacks phosphate metabolism in baker's yeast • Strigolactone allosterically inhibits the high-affinity phosphate transporter Pho84 • A conserved transmembrane pocket in Pho84 is required for strigolactone function • Strigolactone modulates phosphate homeostasis in plant-associated fungi Strigolactones act as both plant hormones and as environmental communication signals to plant-associated fungi. Bradley et al. show that strigolactone modulates phosphate homeostasis in baker's yeast by antagonizing the phosphate transporter Pho84. This strigolactone response is conserved in other fungi, suggesting that yeast will facilitate our understanding of natural plant-fungal communication. [ABSTRACT FROM AUTHOR]

Root parasitic plants in the Orobanchaceae, such as Striga and Orobanche , cause significant damage to crop production. The germination step of these root parasitic plants is induced by host-root-derived strigolactones. After germination, the radicles elongate toward the host and invade the host root. We have previously discovered that a simple amino acid, tryptophan (Trp), as well as its metabolite, the plant hormone indole-3-acetic acid (IAA), can inhibit radicle elongation of Orobanche minor. These results suggest that auxin plays a crucial role in the radicle elongation step in root parasitic plants. In this report, we used various auxin chemical probes to dissect the auxin function in the radicle growth of O. minor and Striga hermonthica. We found that synthetic auxins inhibited radicle elongation. In addition, auxin receptor antagonist, auxinole, rescued the inhibition of radicle growth by exogenous IAA. Moreover, a polar transport inhibitor of auxin, N -1-naphthylphthalamic acid, affected radicle bending. We also proved that exogenously applied Trp is converted into IAA in O. minor seeds, and auxinole partly rescued this radicle elongation. Taken together, our data demonstrate a pivotal role for auxin in radicle growth. Thus, manipulation of auxin function in root parasitic plants should offer a useful approach to combat these parasites. [ABSTRACT FROM AUTHOR]

Salt stress is a key environmental factor altering rice plant growth. Strigolactones (GR24) play a vital role in responding to various abiotic stresses and regulating plant growth. However, the regulatory mechanisms of SLs on rice seedlings under salt stress have not yet been clarified. A pot experiment was undertaken to evaluate the effects of GR24 soaking on the rice variety 'Huanghuazhan' (salt-sensitive) seedling growth, antioxidant metabolism, and endogenous hormones under NaCl stress. Results showed that NaCl stress significantly inhibited rice growth; disrupted antioxidant enzymes activity; and increased the content of soluble proteins (SPs), proline (Pro), malondialdehyde (MDA) and hydrogen–peroxide (H2O2). GR24 significantly improved photosynthetic pigments and antioxidant–enzyme activities, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate–peroxidase (APX); increased SP, ascorbic acid (AsA); and reduced glutathione (GSH) content and MDA, H2O2, and Pro content, resulting in the mitigation of oxidative injury caused by NaCl stress. Moreover, GR24 significantly increased the content of strigolactones (SLs), cytokinin (CTK), auxin (IAA), Gibberellin A3 (GA3), and IAA/ABA and CTK/ABA ratios and decreased the abscisic acid (ABA). Findings indicated that GR24 alleviated oxidative damage caused by NaCl stress by increasing photosynthetic and antioxidant capacity and maintaining the balance of endogenous hormones, thus improving the salt tolerance of rice seedlings. [ABSTRACT FROM AUTHOR]

Strigolactone (SL) is a signal factor that plays a vital role in plants. The application of SL for the storability of horticultural products has recently received attention. In this experiment, fresh-cut apples were treated with SL at diverse concentrations and stored at 4 °C for 10 days, and the changes in quality characteristics, antioxidant system, hydrogen sulfide metabolism, and nitric oxide metabolism were determined. Compared with other treatments, the results showed that SL treatment at 0.50 µmol L−1 had excellent effects on maintaining fruit surface color, weight, firmness, reduced respiration rate, soluble solids content, and electrolyte leakage. SL treatment increased antioxidant enzyme activities, reduced reactive oxygen species (ROS) accumulation, altered the nitric oxide synthase (NOS)-like pathway to promote endogenous NO production in the fruit, and facilitated the L-cysteine-catalyzed process to increase the endogenous hydrogen sulfide (H2S) content. In addition, SL treatment affected the mRNA transcription levels of several genes related to the antioxidant system, H2S metabolism, and NO synthesis, including MdSOD, MdCAT, MdPOD, and MdSAT. Taken together, the results indicated that 0.50 µmol L−1 SL treatment improves the endogenous synthesis of NO and H2S, enhances the antioxidative system, and maintains the quality of fresh-cut apples during their shelf life. Therefore, the present study opens up the possibility of using the exogenous application of strigolactone in the fresh-cut processing industry. [ABSTRACT FROM AUTHOR]

Abstract Due to the high solubility of Cd in water, it is considered a potential toxin which can cause cancer in humans. In plants, it is associated with the development of oxidative stress due to the generation of reactive oxygen species. To overcome this issue, the roles of different plant hormones are vital. Strigolactones, one of such natural plant hormones, show promise in alleviating cadmium toxicity by mitigating its harmful effects. Acidified biochar (AB) can also effectively mitigate cadmium toxicity via ion adsorption and pH buffering. However, the combined effects of strigolactone and AB still need in-depth investigations in the context of existing literature. This study aimed to assess the individual and combined impacts of SLs (0 and 25 µM) and AB (0 and 0.75% w/w) on radish growth under Cd toxicity, i.e., 0 and 20 mg Cd/kg soil. Using a fully randomized design (CRD), each treatment was administered in four replicates. In comparison to the control under 20 mg Cd/kg soil contamination, the results showed that 25 µM strigolactone + 0.75% AB significantly improved the following: radish shoot length (~ 17%), root length (~ 47%), plant fresh weight (~ 28%), plant dry weight (~ 96%), chlorophyll a (~ 43%), chlorophyll b (~ 31%), and total chlorophyll (~ 37%). It was also noted that 0.75% AB was more pronounced in decreasing antioxidant activities than 25 µM strigolactone under 20 mg Cd/ kg soil toxicity. However, performing 25 µM strigolactone + 0.75% AB was far better than the sole application of 25 µM strigolactone and 0.75% AB in decreasing antioxidant activities in radish plants. In conclusion, by regulating antioxidant activities, 25 µM strigolactone + 0.75% AB can increase radish growth in cadmium-contaminated soils.

The article discusses the role of the RAM1 transcription factor in regulating arbuscular mycorrhizal (AM) symbiosis in non-legume plants, specifically focusing on tomato. AM symbiosis is a process where plants form a mutually beneficial relationship with fungi in the soil. The study found that RAM1 may negatively regulate mycorrhization by inhibiting the production of strigolactones, which are chemicals released by the plant to stimulate fungal spore germination. The article also mentions other factors involved in AM symbiosis, such as hormone signaling and transcriptional regulation. Further research is needed to fully understand the complex regulatory mechanisms of AM symbiosis in non-legume plants. [Extracted from the article]

This study uncovers the potential of salicylic acid (SA) and synthetic Strigolactone (GR24) in enhancing menthol biosynthesis and antioxidant defense mechanisms in Mentha piperita L. Our comprehensive analysis, which included a series of controlled experiments and data analysis of the effects of these phytohormones on enzymatic antioxidants catalase (CAT) and ascorbate peroxidase (APX) and non-enzymatic antioxidants, including carotenoids and proline, revealed promising results. The study also examined their impact on lipid peroxidation, hydrogen peroxide levels, and the expression of genes critical to menthol and menthofuran synthesis. The results indicated that SA and GR24 significantly increased menthol production and reduced the levels of menthofuran and pulegone, suggesting upregulation in the plant's innate defense systems. Furthermore, the activities of CAT and APX were elevated, reflecting a strengthened antioxidant response. Interestingly, the menthofuran synthase (MFS) was higher in the control group. At the same time, pulegone reductase (PR) genes and menthol dehydrogenase (MDH) gene expression were upregulated, highlighting the protective effects of SA and GR24. These findings underscore the potential of SA and GR24 to serve as effective bio-stimulants, improving the quality and resilience of peppermint plants and thereby contributing to eco-friendly agricultural practices in pollution-stressed environments. [ABSTRACT FROM AUTHOR]

The fodder soybean (Glycine max) is an excellent leguminous forage with a high protein content and hay yield, cultivated comprehensively in alpine regions, but seasonal drought in northern regions severely impacts the growth of seedlings. Melatonin (MT) and strigolactone (SL) are critical in relieving the restraint of plant growth in water-deficient environments, but the mechanisms of MT- and SL-mediated drought resistance in fodder soybean needs to be explored. This study mainly investigated the potential morphophysiological mechanism of MT and SL treatments in protecting fodder soybean from drought stress. The fodder soybean 'Gongnong 535' was treated with 100 µM MT or 1 µM SL under normal, moderate, and severe water deficit conditions. The results showed that MT and SL treatments enhanced the plant growth parameters and stomatal aperture under drought stress. Moreover, the observed reductions in superoxide ion (O2.-), malondialdehyde (MDA), and relative electrical conductivity (REC), along with enhancements in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as higher levels of ascorbate (AsA), glutathione (GSH), soluble sugar (SS), soluble protein (SP), and free proline (Pro), indicated that MT and SL application effectively alleviated the oxidative damage and prevented the cell membrane disruption caused by drought stress. Additionally, MT and SL treatments improved photosynthesis and growth in fodder soybean seedlings under water stress by adjusting chlorophyll pigments, gas exchange indexes, and chlorophyll fluorescence parameters, as well as endogenous hormone levels. Simultaneously, MT and SL influenced the expression of genes associated with photosynthesis and antioxidant defenses, as well as phytohormone concentrations. Notably, the protective effect of the SL treatment was superior to that of MT in water-deficient conditions. This study contributes to further understanding the defensive mechanism of MT and SL against drought stress. [ABSTRACT FROM AUTHOR]

SUMMARY: Strigolactones (SL) function as plant hormones in control of multiple aspects of plant development, mostly via the regulation of gene expression. Immediate early‐gene regulation by SL remains unexplored due to difficulty in dissecting early from late gene expression responses to SL. We used synthetic SL, rac‐GR24 treatment of protoplasts and RNA‐seq to explore early SL‐induced changes in gene expression over time (5–180 minutes) and discovered rapid, dynamic and SL receptor D14‐dependent regulation of gene expression in response to rac‐GR24. Importantly, we discovered a significant dependence of SL signalling on chromatin remodelling processes, as the induction of a key SL‐induced transcription factor BRANCHED1 requires the SWI/SNF chromatin remodelling ATPase SPLAYED (SYD) and leads to upregulation of a homologue SWI/SNF ATPase BRAHMA. ATAC‐seq profiling of genome‐wide changes in chromatin accessibility in response to rac‐GR24 identified large‐scale changes, with over 1400 differentially accessible regions. These changes in chromatin accessibility often precede transcriptional changes and are likely to harbour SL cis‐regulatory elements. Importantly, we discovered that this early and extensive modification of the chromatin landscape also requires SYD. This study, therefore, provides evidence that SL signalling requires regulation of chromatin accessibility, and it identifies genomic locations harbouring likely SL cis‐regulatory sequences. Significance Statement: We have identified that the significant transcriptomic reprogramming by rac‐GR24 requires extensive changes to chromatin accessibility at over a thousand locations throughout the genome. We showed that two chromatin remodellers, SPLAYED and BRAHMA, are involved in this response. Our findings discovered a new component of gene regulation by the plant hormone strigolactone. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) are plant hormones with significant roles in plant growth, development and environmental interactions. SLs were first discovered to stimulate the germination of parasitic plants such as Striga and Orobanche, but they have now been revealed to regulate a variety of physiological processes in plants. Since their detection as germination stimulants, SLs have received a lot of attention for their several activities in controlling shoot branching, stress responses and symbiotic interactions with beneficial microorganisms. This review examines recent bioinformatics approaches to evaluating SLs and their receptors. By thoroughly exploring the significance of SLs in plant biology, this article highlights the potential for interdisciplinary research to fully use SLs in agriculture and other applications. [ABSTRACT FROM AUTHOR]

One of Nigerian's preferred crops is cowpea(Vigna unguiculata(L)Walp) because it is recognized as a key food and nutritional security legume in Sub Saharan Africa. Striga gesnerioides(Willd.)Vatke is a primary biotic constraint of cowpea production in West Africa. There are currently limited sources of resistance in cowpea germplasm and there exists the potential for resistance breakdown. Hence, the objective of this paper was to evaluate post-emergence Striga gesnerioides damages and determination of phosphate fertilizer containment concentration at low inoculum level in cowpea (Vigna unguiculata (L)Walp.) using appropriate standard method with a bid to meet sustainable development (SD) Goal 2.0 (food security), Twenty five morphological traits comprising seventeen quantitative and eight qualitative traits were evaluated. In this research, assessments of cowpea varieties were carried out to determine phenotypic traits which make them Striga resistant/susceptible. Striga gesnerioides damage of cowpea was post-emergent and not pre-emergent as commonly reported. Zero Striga gesnerioides emergence point was 50 kg/ha TSP. [ABSTRACT FROM AUTHOR]

The effects of exogenous strigolactone (using strigolactone analog GR24) on the cadmium (Cd) accumulation in Solanum nigrum var. humile were studied by a pot experiment. The Cd treatment (0.1 mg/L) inhibited the growth of S. nigrum var. humile, indicating that 0.1 mg/L produced the stress to S. nigrum var. humile. Spraying GR24 at 1 μmol/L did not change plant dry biomass, increased the photosynthetic pigment content and catalase activity, and decreased the peroxidase activity under Cd stress. By contrast, spraying GR24 at 2 μmol/L had no significant effects on these parameters. The superoxide dismutase activity was decreased by GR24 at 1 μmol/L, but increased by GR24 at 2 μmol/L. Nevertheless, both GR24 at 1 and 2 μmol/L increased the Cd contents, bioconcentration factors, and Cd extractions in various plant organs. Compared to Cd treatment, GR24 at 1 and 2 μmol/L increased the shoot Cd extraction by 20.0% and 14.5%, respectively. So, application of exogenous strigolactone could improve the phytoremediation capacity of S. nigrum var. humile. Correlation and grey relational analyses showed that the root Cd content, shoot Cd content, and root Cd extraction were the top three parameters closely related to the shoot Cd extraction. These findings suggest that exogenous strigolactone can effectively promote the Cd accumulation in S. nigrum var. humile, presenting a promising solution to enhance its phytoremediation capacity. [ABSTRACT FROM AUTHOR]

Due to the high solubility of Cd in water, it is considered a potential toxin which can cause cancer in humans. In plants, it is associated with the development of oxidative stress due to the generation of reactive oxygen species. To overcome this issue, the roles of different plant hormones are vital. Strigolactones, one of such natural plant hormones, show promise in alleviating cadmium toxicity by mitigating its harmful effects. Acidified biochar (AB) can also effectively mitigate cadmium toxicity via ion adsorption and pH buffering. However, the combined effects of strigolactone and AB still need in-depth investigations in the context of existing literature. This study aimed to assess the individual and combined impacts of SLs (0 and 25 µM) and AB (0 and 0.75% w/w) on radish growth under Cd toxicity, i.e., 0 and 20 mg Cd/kg soil. Using a fully randomized design (CRD), each treatment was administered in four replicates. In comparison to the control under 20 mg Cd/kg soil contamination, the results showed that 25 µM strigolactone + 0.75% AB significantly improved the following: radish shoot length (~ 17%), root length (~ 47%), plant fresh weight (~ 28%), plant dry weight (~ 96%), chlorophyll a (~ 43%), chlorophyll b (~ 31%), and total chlorophyll (~ 37%). It was also noted that 0.75% AB was more pronounced in decreasing antioxidant activities than 25 µM strigolactone under 20 mg Cd/ kg soil toxicity. However, performing 25 µM strigolactone + 0.75% AB was far better than the sole application of 25 µM strigolactone and 0.75% AB in decreasing antioxidant activities in radish plants. In conclusion, by regulating antioxidant activities, 25 µM strigolactone + 0.75% AB can increase radish growth in cadmium-contaminated soils. [ABSTRACT FROM AUTHOR]

The phytohormones strigolactones (SLs) control root and shoot branching and are exuded from roots into the rhizosphere to stimulate interaction with mycorrhizal fungi. The exuded SLs serve as signaling molecules for the germination of parasitic plants. The broomrape Phelipanche aegyptiaca is a widespread noxious weed in various crop plants, including tomato (Solanum lycopersicum). We have isolated three mutants that impair SL functioning in the tomato variety M82: SHOOT BRANCHING 1 (sb1) and SHOOT BRANCHING 2 (sb2), which abolish SL biosynthesis, and SHOOT BRANCHING 3 (sb3), which impairs SL perception. The over-branching phenotype of the sb mutants resulted in a severe yield loss. The isogenic property of the mutations in a determinate growth variety enabled the quantitative evaluation of the contribution of SL to yield under field conditions. As expected, the mutants sb1 and sb2 were completely resistant to infection by P. aegyptiaca due to the lack of SL in the roots. In contrast, sb3 was more susceptible to P. aegyptiaca than the wild-type M82. The SL concentration in roots of the sb3 was two-fold higher than in the wild type due to the upregulation of the transcription of SL biosynthesis genes. This phenomenon suggests that the steady-state level of root SLs is regulated by a feedback mechanism that involves the SL signaling pathway. Surprisingly, grafting wild-type varieties on sb1 and sb2 rootstocks eliminated the branching phenotype and yield loss, indicating that SL synthesized in the shoots is sufficient to control shoot branching. Moreover, commercial tomato varieties grafted on sb1 were protected from P. aegyptiaca infection without significant yield loss, offering a practical solution to the broomrape crisis. [ABSTRACT FROM AUTHOR]

To adapt to fluctuations in light intensity, temperatures, and water/nutrient availability, plants have to dynamically and flexibly adjust their metabolism and growth processes. Specifically, hormone synthesis and signal transduction promptly respond to environmental stimuli. Understanding the mechanisms by which plants adapt to their environment is a hot spot of plant biology research. In this editorial, we provide a summary of recent advances in the roles and underlying mechanisms of abscisic acid (ABA) in coping with various stresses. Additionally, we highlight the functions of newly discovered hormones such as strigolactone. Furthermore, we emphasize future research directions aimed at gaining a deeper understanding of how plants maintain cellular homeostasis with the goal of improving crop yield in the background of global change.

Strigolactones (SLs) are a unique and novel class of phytohormones that regulate numerous processes of growth and development in plants. Besides their endogenous functions as hormones, SLs are exuded by plant roots to stimulate critical interactions with symbiotic fungi but can also be exploited by parasitic plants to trigger their seed germination. In the past decade, since their discovery as phytohormones, rapid progress has been made in understanding the SL biosynthesis and signaling pathway. Of particular interest are the diversification of natural SLs and their exact mode of perception, selectivity, and hydrolysis by their dedicated receptors in plants. Here we provide an overview of the emerging field of SL perception with a focus on the diversity of canonical, non-canonical, and synthetic SL probes. Moreover, this review offers useful structural insights into SL perception, the precise molecular adaptations that define receptor-ligand specificities, and the mechanisms of SL hydrolysis and its attenuation by downstream signaling components.

Abstract Salinity stress can significantly delay plant growth. It can disrupt water and nutrient uptake, reducing crop yields and poor plant health. The use of strigolactone can be an effective technique to overcome this issue. Strigolactone enhances plant growth by promoting root development and improvement in physiological attributes. The current pot study used strigolactone to amend chili under no salinity and salinity stress environments. There were four treatments, i.e., 0, 10µM strigolactone, 20µM strigolactone and 30µM strigolactone. All treatments were applied in four replications following a completely randomized design (CRD). Results showed that 20µM strigolactone caused a significant increase in chili plant height (21.07%), dry weight (33.60%), fruit length (19.24%), fruit girth (35.37%), and fruit yield (60.74%) compared to control under salinity stress. Significant enhancement in chili chlorophyll a (18.65%), chlorophyll b (43.52%), and total chlorophyll (25.09%) under salinity stress validated the effectiveness of 20µM strigolactone application as treatment over control. Furthermore, improvement in nitrogen, phosphorus, and potassium concentration in leaves confirmed the efficient functioning of 20µM strigolactone compared to other concentrations under salinity stress. The study concluded that 20µM strigolactone is recommended for mitigating salinity stress in chili plants. Growers are advised to apply 20µM strigolactone to enhance their chili production under salinity stress.

Summary: Arabidopsis thaliana (Arabidopsis) shoot architecture is largely determined by the pattern of axillary buds that grow into lateral branches, the regulation of which requires integrating both local and systemic signals.Nodal explants – stem explants each bearing one leaf and its associated axillary bud – are a simplified system to understand the regulation of bud activation. To explore signal integration in bud activation, we characterised the growth dynamics of buds in nodal explants in key mutants and under different treatments.We observed that isolated axillary buds activate in two genetically and physiologically separable phases: a slow‐growing lag phase, followed by a switch to rapid outgrowth. Modifying BRANCHED1 expression or the properties of the auxin transport network, including via strigolactone application, changed the length of the lag phase. While most interventions affected only the length of the lag phase, strigolactone treatment and a second bud also affected the rapid growth phase.Our results are consistent with the hypothesis that the slow‐growing lag phase corresponds to the time during which buds establish canalised auxin transport out of the bud, after which they enter a rapid growth phase. Our work also hints at a role for auxin transport in influencing the maximum growth rate of branches. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs), a class of plant apocarotenoids, serve dual roles as rhizosphere-signaling molecules and plant hormones. Orobanchol, a major naturally occurring SL, along with its various derivatives, has been detected in the root exudates of plants of the Fabaceae family. Medicaol, fabacyl acetate, and orobanchyl acetate were identified in the root exudates of barrelmedic (Medicago truncatula), pea (Pisum sativum), and cowpea (Vigna unguiculata), respectively. Although the biosynthetic pathway leading to orobanchol production has been elucidated, the biosynthetic pathways of the orobanchol derivatives have not yet been fully elucidated. Here, we report the identification of 2-oxoglutaratedependent dioxygenases (DOXs) and BAHD acyltransferases responsible for converting orobanchol to these derivatives in Fabaceae plants. First, the metabolic pathways downstream of orobanchol were analyzed using substrate feeding experiments. Prohexadione, an inhibitor of DOX inhibits the conversion of orobanchol to medicaol in barrel medic. The DOX inhibitor also reduced the formation of fabacyl acetate and fabacol, a precursor of fabacyl acetate, in pea. Subsequently, we utilized a dataset based on comparative transcriptome analysis to select a candidate gene encoding DOX for medicaol synthase in barrel medic. Recombinant proteins of the gene converted orobanchol to medicaol. The candidate genes encoding DOX and BAHD acyltransferase for fabacol synthase and fabacol acetyltransferase, respectively, were selected by co-expression analysis in pea. The recombinant proteins of the candidate genes converted orobanchol to fabacol and acetylated fabacol. Furthermore, fabacol acetyltransferase and its homolog in cowpea acetylated orobanchol. The kinetics and substrate specificity analyses revealed high affinity and strict recognition of the substrates of the identified enzymes. These findings shed light on the molecular mechanisms underlying the structural diversity of SLs. [ABSTRACT FROM AUTHOR]

Key message: Exogenous SL positively regulates pepper DS by altering the root morphology, photosynthetic character, antioxidant enzyme activity, stomatal behavior, and SL-related gene expression. Drought stress (DS) has always been a problem for the growth and development of crops, causing significant negative impacts on crop productivity. Strigolactone (SL) is a newly discovered class of plant hormones that are involved in plants’ growth and development and environmental stresses. However, the role of SL in response to DS in pepper remains unknown. DS considerably hindered photosynthetic pigments content, damaged root architecture system, and altered antioxidant machinery. In contrast, SL application significantly restored pigment concentration modified root architecture system, and increased relative chlorophyll content (SPAD). Additionally, SL treatment reduced oxidative damage by reducing hydrogen peroxide (H2O2) (24–57%) and malondialdehyde (MDA) (79–89%) accumulation in pepper seedlings. SL-pretreated pepper seedlings showed significant improvement in antioxidant enzyme activity, proline accumulation, and soluble sugar content. Furthermore, SL-related genes (CcSMAX2, CcSMXL6, and CcSMXL3) were down-regulated under DS. These findings suggest that the foliar application of SL can alleviate the adverse effects of drought tolerance by up-regulating chlorophyll content and activating antioxidant defense mechanisms. [ABSTRACT FROM AUTHOR]

Strigolactone can improve the tolerance of plants to abiotic stress. To improve the phytoremediation capacity of cadmium (Cd) hyperaccumulator Galinsoga parviflora Cav., the effects of strigolactone (using strigolactone analog GR24 with the concentration of 1 and 2 μmol/L) on the Cd accumulation of G. parviflora were studied. Cd treatment at 0.1 mg/L inhibited the growth of G. parviflora. Under Cd stress (0.1 mg/L), GR24 had no significant effect on the biomass and catalase activity of G. parviflora, while it decreased the peroxidase activity and increased the superoxide dismutase activity. In addition, GR24 decreased the root Cd content and root Cd extraction. GR24 at 1 μmol/L increased the shoot Cd content, shoot Cd extraction, bioconcentration factor, and translocation factor, while at 2 μmol/L, the opposite effect was observed. When the concentration of GR24 was 1 μmol/L, the shoot Cd content and shoot Cd extraction increased by 8.75% and 12.35%, respectively, compared with control. Moreover, correlation and grey relational analyses showed that the translocation factor, shoot Cd content, and plant height were the top three most highly correlated parameters with the shoot Cd extraction. These findings suggest that GR24 at 1 μmol/L can improve the phytoremediation capacity of G. parviflora for Cd. [ABSTRACT FROM AUTHOR]

Salinity stress can significantly delay plant growth. It can disrupt water and nutrient uptake, reducing crop yields and poor plant health. The use of strigolactone can be an effective technique to overcome this issue. Strigolactone enhances plant growth by promoting root development and improvement in physiological attributes. The current pot study used strigolactone to amend chili under no salinity and salinity stress environments. There were four treatments, i.e., 0, 10µM strigolactone, 20µM strigolactone and 30µM strigolactone. All treatments were applied in four replications following a completely randomized design (CRD). Results showed that 20µM strigolactone caused a significant increase in chili plant height (21.07%), dry weight (33.60%), fruit length (19.24%), fruit girth (35.37%), and fruit yield (60.74%) compared to control under salinity stress. Significant enhancement in chili chlorophyll a (18.65%), chlorophyll b (43.52%), and total chlorophyll (25.09%) under salinity stress validated the effectiveness of 20µM strigolactone application as treatment over control. Furthermore, improvement in nitrogen, phosphorus, and potassium concentration in leaves confirmed the efficient functioning of 20µM strigolactone compared to other concentrations under salinity stress. The study concluded that 20µM strigolactone is recommended for mitigating salinity stress in chili plants. Growers are advised to apply 20µM strigolactone to enhance their chili production under salinity stress. [ABSTRACT FROM AUTHOR]

Axillary bud outgrowth, a key factor in ratoon rice yield formation, is regulated by several phytohormone signals. The regulatory mechanism of key genes underlying ratoon buds in response to phytohormones in ratoon rice has been less reported. In this study, GR24 (a strigolactone analogue) was used to analyze the ratooning characteristics in rice cultivar Huanghuazhan (HHZ). Results show that the elongation of the axillary buds in the first seasonal rice was significantly inhibited and the ratoon rate was reduced at most by up to 40% with GR24 treatment. Compared with the control, a significant reduction in the content of auxin and cytokinin in the second bud from the upper spike could be detected after GR24 treatment, especially 3 days after treatment. Transcriptome analysis suggested that there were at least 742 and 2877 differentially expressed genes (DEGs) within 6 h of GR24 treatment and 12 h of GR24 treatment, respectively. Further bioinformatics analysis revealed that GR24 treatment had a significant effect on the homeostasis and signal transduction of cytokinin and auxin. It is noteworthy that the gene expression levels of OsCKX1, OsCKX2, OsGH3.6, and OsGH3.8, which are involved in cytokinin or auxin metabolism, were enhanced by the 12 h GR24 treatment. Taken overall, this study showed the gene regulatory network of auxin and cytokinin homeostasis to be regulated by strigolactone in the axillary bud outgrowth of ratoon rice, which highlights the importance of these biological pathways in the regulation of axillary bud outgrowth in ratoon rice and would provide theoretical support for the molecular breeding of ratoon rice. [ABSTRACT FROM AUTHOR]

ABSTRACT Plants play an essential role in the ecological cycle; however, they face numerous global biotic and abiotic stress factors. The capacity of plants to survive in adverse conditions is called stress tolerance. Drought stress is among the major stresses faced by plants, as arid conditions affect plant development and productivity, crop yield, relative water content, nutrient intake, photosynthesis, dry matter accumulation, and respiration. Hormones play an essential role in plant stress metabolism. Until recently, it was thought that plant hormones consisted of five groups: auxin, gibberellin, cytokinin, abscisic acid, and ethylene. However, other substances synthesized by plants, such as jasmonates, brassinosteroids, salicylic acid, and nitric oxide, have also shown critical vital functions in the plant, like the hormones. Another hormone in these substances is strigolactone (SL), which has been reported to perform essential functions in stress physiology. This research investigated the effects of SL applications on drought stress on 1103 Paulsen American Grapevine Rootstock. GR24, a synthetic analog of SLs, was applied to grapevine rootstock. Physical and biochemical changes were determined (chlorophyll, membrane injurity, prolin, lipid peroxidation, soluble protein, superoxide dismutase, ascorbate peroxidase activities, phenolic compounds, plant hormones, and mineral elements). The results show that GR24 applications effectively alleviate the harmful effects of drought stress in most features.

One of Nigerian’s preferred crops is cowpea(Vigna unguiculata(L)Walp) because it is recognized as a key food and nutritional security legume in Sub Saharan Africa.Striga gesnerioides(Willd.)Vatke is a primary biotic constraint of cowpea production in West Africa. There are currently limited sources of resistance in cowpea germplasm and there exists the potential for resistance breakdown . Hence,the objective of this paper was to evaluate post-emergence Striga gesnerioides damages and determination of phosphate fertilizer containment concentration at low inoculum level in cowpea (Vigna unguiculata (L)Walp.) using appropriate standard method with a bid to meet sustainable development (SD) Goal 2.0 (food security), Twenty five morphological traits comprising seventeen quantitative and eight qualitative traits were evaluated. In this research,assessments of cowpea varieties were carried out to determine phenotypic traits which make them Striga resistant/susceptible. Striga gesnerioides damage of cowpea was post-emergent and not pre-emergent as commonly reported. Zero Striga gesnerioides emergence point was 50 kg/ha TSP.

Abstract Chromium (Cr) stress significantly hinders crop production by disrupting nutrient uptake, impairing plant growth, and contaminating soil, posing a substantial threat to agricultural sustainability. The use of deashed biochar (DAB) and strigolactone can be an effective solution to mitigate this issue. Deashed biochar enhances crop production by improving soil structure, water retention, and nutrient availability while mitigating the bioavailability of toxic substances. Strigolactone boosts plant growth by stimulating root growth, branching, shoot formation, and overall plant physiology. Nevertheless, the scientific rationale behind their collective use as an amendment to counter Cr stress remains to be substantiated. Therefore, in this study, a blend of DAB and strigolactone was employed as additives in radish cultivation, both in the absence of Cr stress and under the influence of 200Cr stress. Four treatments, i.e., 0, 20µM Strigolactone, DAB, and 20µM Strigolactone + DAB, were applied in four replications following a completely randomized design. Results demonstrate that 20µM Strigolactone + DAB produced significant improvement in radish shoot length (27.29%), root length (45.60%), plant fresh weight (33.25%), and plant dry weight (78.91%), compared to the control under Cr stress. Significant enrichment in radish chlorophyll a (20.41%), chlorophyll b (58.53%), and total chlorophyll (31.54%) over the control under Cr stress, prove the efficacy of 20µM Strigolactone + DAB treatment. In conclusion, 20µM Strigolactone + DAB is the recommended amendment for mitigating Cr stress in radish. Farmers should consider using Strigolactone + DAB amendments to combat Cr stress and enhance radish growth, contributing to a more resilient agricultural ecosystem.

Strigolactone (SL) is a signal factor that plays a vital role in plants. The application of SL for the storability of horticultural products has recently received attention. In this experiment, fresh-cut apples were treated with SL at diverse concentrations and stored at 4 °C for 10 days, and the changes in quality characteristics, antioxidant system, hydrogen sulfide metabolism, and nitric oxide metabolism were determined. Compared with other treatments, the results showed that SL treatment at 0.50 µmol L−1 had excellent effects on maintaining fruit surface color, weight, firmness, reduced respiration rate, soluble solids content, and electrolyte leakage. SL treatment increased antioxidant enzyme activities, reduced reactive oxygen species (ROS) accumulation, altered the nitric oxide synthase (NOS)-like pathway to promote endogenous NO production in the fruit, and facilitated the L-cysteine-catalyzed process to increase the endogenous hydrogen sulfide (H2S) content. In addition, SL treatment affected the mRNA transcription levels of several genes related to the antioxidant system, H2S metabolism, and NO synthesis, including MdSOD, MdCAT, MdPOD, and MdSAT. Taken together, the results indicated that 0.50 µmol L−1 SL treatment improves the endogenous synthesis of NO and H2S, enhances the antioxidative system, and maintains the quality of fresh-cut apples during their shelf life. Therefore, the present study opens up the possibility of using the exogenous application of strigolactone in the fresh-cut processing industry.

Salt stress is a key environmental factor altering rice plant growth. Strigolactones (GR24) play a vital role in responding to various abiotic stresses and regulating plant growth. However, the regulatory mechanisms of SLs on rice seedlings under salt stress have not yet been clarified. A pot experiment was undertaken to evaluate the effects of GR24 soaking on the rice variety ‘Huanghuazhan’ (salt-sensitive) seedling growth, antioxidant metabolism, and endogenous hormones under NaCl stress. Results showed that NaCl stress significantly inhibited rice growth; disrupted antioxidant enzymes activity; and increased the content of soluble proteins (SPs), proline (Pro), malondialdehyde (MDA) and hydrogen–peroxide (H2O2). GR24 significantly improved photosynthetic pigments and antioxidant–enzyme activities, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate–peroxidase (APX); increased SP, ascorbic acid (AsA); and reduced glutathione (GSH) content and MDA, H2O2, and Pro content, resulting in the mitigation of oxidative injury caused by NaCl stress. Moreover, GR24 significantly increased the content of strigolactones (SLs), cytokinin (CTK), auxin (IAA), Gibberellin A3 (GA3), and IAA/ABA and CTK/ABA ratios and decreased the abscisic acid (ABA). Findings indicated that GR24 alleviated oxidative damage caused by NaCl stress by increasing photosynthetic and antioxidant capacity and maintaining the balance of endogenous hormones, thus improving the salt tolerance of rice seedlings.

Chromium (Cr) stress significantly hinders crop production by disrupting nutrient uptake, impairing plant growth, and contaminating soil, posing a substantial threat to agricultural sustainability. The use of deashed biochar (DAB) and strigolactone can be an effective solution to mitigate this issue. Deashed biochar enhances crop production by improving soil structure, water retention, and nutrient availability while mitigating the bioavailability of toxic substances. Strigolactone boosts plant growth by stimulating root growth, branching, shoot formation, and overall plant physiology. Nevertheless, the scientific rationale behind their collective use as an amendment to counter Cr stress remains to be substantiated. Therefore, in this study, a blend of DAB and strigolactone was employed as additives in radish cultivation, both in the absence of Cr stress and under the influence of 200Cr stress. Four treatments, i.e., 0, 20µM Strigolactone, DAB, and 20µM Strigolactone + DAB, were applied in four replications following a completely randomized design. Results demonstrate that 20µM Strigolactone + DAB produced significant improvement in radish shoot length (27.29%), root length (45.60%), plant fresh weight (33.25%), and plant dry weight (78.91%), compared to the control under Cr stress. Significant enrichment in radish chlorophyll a (20.41%), chlorophyll b (58.53%), and total chlorophyll (31.54%) over the control under Cr stress, prove the efficacy of 20µM Strigolactone + DAB treatment. In conclusion, 20µM Strigolactone + DAB is the recommended amendment for mitigating Cr stress in radish. Farmers should consider using Strigolactone + DAB amendments to combat Cr stress and enhance radish growth, contributing to a more resilient agricultural ecosystem. [ABSTRACT FROM AUTHOR]

Strigolactones and abscisic acid (ABA) are apocarotenoid-derived plant hormones. Their biosynthesis starts with the conversion of trans -carotenes into cis forms, which serve as direct precursors. Iron-containing DWARF27 isomerases were shown to catalyse or contribute to the trans / cis conversions of these precursor molecules. D27 converts trans -β-carotene into 9- cis -β-carotene, which is the first committed step in strigolactone biosynthesis. Recent studies found that its paralogue, D27-LIKE1, also catalyses this conversion. A crucial step in ABA biosynthesis is the oxidative cleavage of 9- cis -violaxanthin and/or 9- cis -neoxanthin, which are formed from their trans isomers by unknown isomerases. Several lines of evidence point out that D27-like proteins directly or indirectly contribute to 9- cis -violaxanthin conversion, and eventually ABA biosynthesis. Apparently, the diversity of D27-like enzymatic activity is essential for the optimization of cis / trans ratios, and hence act to maintain apocarotenoid precursor pools. In this review, we discuss the functional divergence and redundancy of D27 paralogues and their potential direct contribution to ABA precursor biosynthesis. We provide updates on their gene expression regulation and alleged Fe–S cluster binding feature. Finally, we conclude that the functional divergence of these paralogues is not fully understood and we provide an outlook on potential directions in research. [ABSTRACT FROM AUTHOR]

Santalum album L. (Santalaceae) is an endangered tree species with high economic potential. To improve its cultivation, the role of strigolactone on the somatic embryogenesis of Santalum leaves was analyzed. Leaves were cultivated in vitro using GR24 (a synthetic analogue of strigolactone) at various concentrations (from 0.1 to 1.0 mg L−1) and meta-Topolin (mT), and integrated microscopy of the somatic embryos was used to describe the structural developments underlying the ontogenesis from the leaf under the influence of GR24. The results showed that Murashige and Skoog medium containing 0.75 mg L−1 GR24 produced a maximum percentage (92.0%) of somatic embryos from the leaf surface and cut ends. Weekly microscopic examinations of cultured tissues showed callogenic primary cell masses and minor vascular bundles along the lamina after 3 wk. The proliferation of these primary cell masses led to the emergence of embryogenic outgrowths from leaf surfaces. The areas undergoing intense cell divisions possessed prominent nuclei. The microscopic examinations confirmed the distinctive developmental stages (globular, heart-shaped, and bipolar structures) of somatic embryos. The highest shoot regeneration frequency (88.9%) and shootlet proliferation were aided by the combined incorporation of 0.5 mg L−1mT and 0.25 mg L−1 GR24. The regenerated plantlets were rooted and acclimatized successfully under ex vitro conditions with 91.0% survival in field conditions and possessed a normal phenotypic appearance. The described somatic embryogenic protocol can be effectively utilized for large-scale plantlet production, long-term storage, and genetic engineering studies in this multipotent tree species. [ABSTRACT FROM AUTHOR]

Tiller number greatly contributes to grain yield in wheat. Using ethylmethanesulfonate mutagenesis, we previously discovered the oligo-tillering mutant ot1. The tiller number was significantly lower in ot1 than in the corresponding wild type from the early tillering stage until the heading stage. Compared to the wild type, the thousand-grain weight and grain length were increased by 15.41% and 31.44%, respectively, whereas the plant height and spike length were decreased by 26.13% and 37.25%, respectively. Transcriptomic analysis was conducted at the regreening and jointing stages to identify differential expressed genes (DEGs). Functional enrichment analysis with the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) databases showed differential expression of genes associated with ADP binding, transmembrane transport, and transcriptional regulation during tiller development. Differences in tiller number in ot1 led to the upregulation of genes in the strigolactone (SL) and abscisic acid (ABA) pathways. Specifically, the SL biosynthesis genes DWARF (D27), D17, D10, and MORE AXILLARY GROWTH 1 (MAX1) were upregulated by 3.37- to 8.23-fold; the SL signal transduction genes D14 and D53 were upregulated by 1.81- and 1.32-fold, respectively; the ABA biosynthesis genes 9-CIS-EPOXICAROTENOID DIOXIGENASE 3 (NCED3) and NCED5 were upregulated by 1.66- and 3.4-fold, respectively; and SNF1-REGULATED PROTEIN KINASE2 (SnRK2) and PROTEIN PHOSPHATASE 2C (PP2C) genes were upregulated by 1.30- to 4.79-fold. This suggested that the tiller number reduction in ot1 was due to alterations in plant hormone pathways. Genes known to promote tillering growth were upregulated, whereas those known to inhibit tillering growth were downregulated. For example, PIN-FORMED 9 (PIN9), which promotes tiller development, was upregulated by 8.23-fold in ot1; Ideal Plant Architecture 1 (IPA1), which inhibits tiller development, was downregulated by 1.74-fold. There were no significant differences in the expression levels of TILLER NUMBER 1 (TN1) or TEOSINTE BRANCHED 1 (TB1), indicating that the tiller reduction in ot1 was not controlled by known genes. Our findings provide valuable data for subsequent research into the genetic bases and regulatory mechanisms of wheat tillering. [ABSTRACT FROM AUTHOR]

Dwarfing is one of the common phenotypic variations in asexually reproduced progeny of banana, and dwarfed banana is not only windproof and anti-fallout but also effective in increasing acreage yield. As a key gene in the strigolactone signalling pathway, DWARF53 (D53) plays an important role in the regulation of the height of plants. In order to gain insight into the function of the banana D53 gene, this study conducted genome-wide identification of banana D53 gene based on the M. acuminata, M. balbisiana and M. itinerans genome database. Analysis of MaD53 gene expression under high temperature, low temperature and osmotic stress based on transcriptome data and RT-qPCR was used to analyse MaD53 gene expression in different tissues as well as in different concentrations of GA and SL treatments. In this study, we identified three MaD53, three MbD53 and two MiD53 genes in banana. Phylogenetic tree analysis showed that D53 Musa are equally related to D53 Asparagales and Poales. Both high and low-temperature stresses substantially reduced the expression of the MaD53 gene, but osmotic stress treatments had less effect on the expression of the MaD53 gene. GR24 treatment did not significantly promote the height of the banana, but the expression of the MaD53 gene was significantly reduced in roots and leaves. GA treatment at 100 mg/L significantly promoted the expression of the MaD53 gene in roots, but the expression of this gene was significantly reduced in leaves. In this study, we concluded that MaD53 responds to GA and SL treatments, but "Yinniaijiao" dwarf banana may not be sensitive to GA and SL. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) represent a recently identified class of plant hormones that are crucial for plant tillering and mycorrhizal symbiosis. The D14 gene, an essential receptor within the SLs signaling pathway, has been well-examined in crops, like rice (Oryza sativa L.) and Arabidopsis (Arabidopsis thaliana L.), yet the research on its influence in maize (Zea mays L.) remains scarce. This study successfully clones and establishes Arabidopsis D14 gene overexpression lines (OE lines). When compared with the wild type (WT), the OE lines exhibited significantly longer primary roots during germination. By seven weeks of age, these lines showed reductions in plant height and tillering, alongside slight decreases in rosette and leaf sizes, coupled with early aging symptoms. Fluorescence-based quantitative assays indicated notable hormonal fluctuations in OE lines versus the WT, implying that D14 overexpression disrupts plant hormonal homeostasis. The OE lines, exposed to cold, drought, and sodium chloride stressors during germination, displayed an especially pronounced resistance to drought. The drought resistance of OE lines, as evident from dehydration–rehydration assays, outmatched that of the WT lines. Additionally, under drought conditions, the OE lines accumulated less reactive oxygen species (ROS) as revealed by the assessment of the related physiological and biochemical parameters. Upon confronting the pathogens Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), post-infection, fluorescence quantitative investigations showed a significant boost in the salicylic acid (SA)-related gene expression in OE lines compared to their WT counterparts. Overall, our findings designate the SL receptor D14 as a key upregulator of drought tolerance and a regulator in the biotic stress response, thereby advancing our understanding of the maize SL signaling pathway by elucidating the function of the pivotal D14 gene. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) are a class of terpenoid lactones initially identified as seed germination stimulants for root parasitic plants more than 50 years ago. Long after this initial discovery, SLs were re-characterized as the symbiotic signals for arbuscular mycorrhizal fungi that supply inorganic nutrients, such as phosphate, to their host plants. In 2008, SLs were found to be endogenous plant hormones that regulate shoot branching in plants. The discovery of SLs as a new class of plant hormones has significantly advanced research in this field. Studies over the past 15 years have elucidated almost the entire pathway of SL biosynthesis and the overall mechanism of its signaling. This review summarizes research on the SL biosynthetic pathway, and the current state of knowledge of the SL perception mechanism. [ABSTRACT FROM AUTHOR]

Key message: Strigolactone has the potential to influence hormone metabolism, in addition to having a role in inhibiting axillary bud elongation, which could be regulated by the expression of phytohormones-related genes. The elongation of axillary buds affects the economic benefits of tobacco. In this study, it was investigated the effect of strigolactone (SL) on the elongation of tobacco axillary buds and its endogenous hormone metabolism and related gene expression by applying the artificial analog of SL, GR24, and an inhibitor of SL synthesis, TIS-108, to the axillary buds. The results showed that the elongation of axillary buds was significantly inhibited by GR24 on day 2 and day 9. Ultra-high-performance liquid-chromatography-mass spectrometry results further showed that SL significantly affected the metabolism of endogenous plant hormones, altering both their levels and the ratios between each endogenous hormone. Particularly, the levels of auxin (IAA), trans-zeatin-riboside (tZR), N6-(∆2-isopentenyl) adenine (iP), gibberellin A4 (GA4), jasmonic acid (JA), and jasmonoyl isoleucine (JA-Ile) were decreased after GR24 treatment on day 9, but the levels of 1-aminocyclopropane-1-carboxylic acid (ACC) and gibberellin A1 (GA1) were significantly increased. Further analysis of endogenous hormonal balance revealed that after the treatment with GR24 on day 9, the ratio of IAA to cytokinin (CTK) was markedly increased, but the ratios of IAA to abscisic acid (ABA), salicylic acid (SA), ACC, JAs, and, GAs were notably decreased. In addition, according to RNA-seq analysis, multiple differentially expressed genes were found, such as GH3.1, AUX/IAA, SUAR20, IPT, CKX1, GA2ox1, ACO3, ERF1, PR1, and HCT, which may play critical roles in the biosynthesis, deactivation, signaling pathway of phytohormones, and the biosynthesis of flavonoids to regulate the elongation of axillary buds in tobacco. This work lays the certain theoretical foundation for the application of SL in regulating the elongation of axillary buds of tobacco. [ABSTRACT FROM AUTHOR]

This article explores the role of brassinosteroids (BRs) in regulating bud outgrowth and crop architecture. Short stature crops developed during the green revolution disrupted the gibberellin (GA) pathway, leading to reduced height but increased tillering. BRs have emerged as an alternative dwarfing pathway that can decouple tillering from height. The article discusses how BRs integrate with the branching signaling network, particularly through the transcription factor TB1, and highlights the potential for genetic manipulation of BR biosynthesis or signaling components to modify shoot architecture. Further research is needed to understand the effects of BRs on other branching hormones and to uncover new targets for modifying crop architecture. [Extracted from the article]

Tillering is an important part in strawberry growth, and strawberries can reproduce nutritionally through stolons to generate genetically stable offspring. However, excessive tillering during the fruit-growing stage can negatively impact fruit yield and quality. In this study, different concentrations of exogenous rac-GR24 (GR24) are used to treat the strawberry plants. It was found that GR24 effectively inhibited the sprouting of strawberry stolons, while promoting the growth of the stems and leaves. Among the treatments, the most effective concentration was found to be 5 μmol/L GR24. This treatment resulted in a decrease in the glucose content in the strawberry crowns and also caused changes in the contents of two endogenous phytohormones, gibberellic acid (GA3) and trans-zeatin riboside (tZR). Transcriptome data further suggested that exogenous GR24 may inhibit strawberry plant tillering by affecting various phytohormone signaling pathways and the sugar metabolism pathway. In 5 μmol/L GR24-treated plants, the expression level of type-B response regulator (B-ARR) was down-regulated and the expression level of CYTOKININ RESPONSE 1 (CRE1), histidine-containing phosphotransfer protein (AHP), and type-A response regulator (A-ARR) were up-regulated, suggesting the inhibition of the cytokinin (CTK) signaling pathway. The down-regulation of auxin (AUX) and auxin response factor (ARF), as well as the up-regulation of auxin/indole-3-acetic acid (AUX/IAA), led to the inhibition of the indole-3-acetic acid (IAA) signaling pathway. Additionally, the up-regulation of pyrabactin resistance 1/ pyrabactin resistance 1-like (PYR/PYL), non-fermenting 1-related protein kinase 2 (SnRK2), and ABRE binding factors (ABF) and the down-regulation of protein phosphatase 2C (PP2C) were observed in the up-regulated abscisic acid (ABA) signaling pathways. In the sugar metabolism pathway, the up-regulation of invertase (INV), hexokinase (HK), and fructokinase (FRK) and the down-regulation of trehalase (TREH) and beta-amylase (BMY) led to a decreased glucose synthesis and an increased glucose consumption. Therefore, GR24 can effectively inhibit strawberry plant tillering through these pathways, making it an effective reagent for tillering inhibition. [ABSTRACT FROM AUTHOR]

Poa pratensis is widely distributed in cold temperate regions and can be used as a species for stress restoration and as a forage for livestock. Studying the genetic characteristics of tillering occurrence in bluegrass provides a theoretical basis for studying plant yield formation, environmental adaptation, and improving survival competitiveness. The regulating effects of endogenous hormone IAA content and the expression of related genes ARF1, ARF12, ARF14, ZT content and the expression of related genes CKX2, CKX3, CKX4, SL content and the expression of related genes D14-like, D14.1-like and D14 in wild Kentucky bluegrass were investigated. Kentucky bluegrass from Sunan and Qingshui was used to evaluate the influence of hormone and gene expression on tillering behavior. Endogenous hormone contents and expression levels of related genes in stems and roots of both materials were measured at prophase, peak, and anaphase of tillering. The results showed that among the three materials, the Sunan material had a better tillering ability for Poa pratensis, while the Qingshui material had poorer tillering ability. The downregulation of CKX2, CKX3, and CKX4 gene expression levels promotes the synthesis of ZT, thereby improving the tillering ability of the germplasm. Upregulation of ARF14, D14, and D14.1-like gene expression levels enhances the synthesis of IAA and SL, thereby inhibiting tillering. More importantly, the interaction between hormones affects the tillering ability of bluegrass, and high levels of ZT/IAA, ZT/SL, and ZT/(IAA+SL) values promote tillering. In summary, this study reveals the mechanism by which hormones regulate the occurrence of tillering in Kentucky bluegrass, providing a theoretical basis for understanding the genetic characteristics of plant type, effectively regulating tillering, studying yield development, environmental adaptation, and improving survival rate. [ABSTRACT FROM AUTHOR]

Plants, the cornerstone of life on Earth, are constantly struggling with a number of challenges arising from both biotic and abiotic stressors. To overcome these adverse factors, plants have evolved complex defense mechanisms involving both a number of cell signaling pathways and a complex network of interactions with microorganisms. Among these interactions, the relationship between symbiotic arbuscular mycorrhizal fungi (AMF) and strigolactones (SLs) stands as an important interplay that has a significant impact on increased resistance to environmental stresses and improved nutrient uptake and the subsequent enhanced plant growth. AMF establishes mutualistic partnerships with plants by colonizing root systems, and offers a range of benefits, such as increased nutrient absorption, improved water uptake and increased resistance to both biotic and abiotic stresses. SLs play a fundamental role in shaping root architecture, promoting the growth of lateral roots and regulating plant defense responses. AMF can promote the production and release of SLs by plants, which in turn promote symbiotic interactions due to their role as signaling molecules with the ability to attract beneficial microbes. The complete knowledge of this synergy has the potential to develop applications to optimize agricultural practices, improve nutrient use efficiency and ultimately increase crop yields. This review explores the roles played by AMF and SLs in plant development and stress tolerance, highlighting their individual contributions and the synergistic nature of their interaction. [ABSTRACT FROM AUTHOR]

Drought stress significantly restricts the growth, yield, and quality of peppers. Strigolactone (SL), a relatively new plant hormone, has shown promise in alleviating drought-related symptoms in pepper plants. However, there is limited knowledge on how SL affects the gene expression in peppers when exposed to drought stress (DS) after the foliar application of SL. To explore this, we conducted a thorough physiological and transcriptome analysis investigation to uncover the mechanisms through which SL mitigates the effects of DS on pepper seedlings. DS inhibited the growth of pepper seedlings, altered antioxidant enzyme activity, reduced relative water content (RWC), and caused oxidative damage. On the contrary, the application of SL significantly enhanced RWC, promoted root morphology, and increased leaf pigment content. SL also protected pepper seedlings from drought-induced oxidative damage by reducing MDA and H2O2 levels and maintaining POD, CAT, and SOD activity. Moreover, transcriptomic analysis revealed that differentially expressed genes were enriched in ribosomes, ABC transporters, phenylpropanoid biosynthesis, and Auxin/MAPK signaling pathways in DS and DS + SL treatment. Furthermore, the results of qRT-PCR showed the up-regulation of AGR7, ABI5, BRI1, and PDR4 and down-regulation of SAPK6, NTF4, PYL6, and GPX4 in SL treatment compared with drought-only treatment. In particular, the key gene for SL signal transduction, SMXL6, was down-regulated under drought. These results elucidate the molecular aspects underlying SL-mediated plant DS tolerance, and provide pivotal strategies for effectively achieving pepper drought resilience. [ABSTRACT FROM AUTHOR]

Cucumber (Cucumis sativus L.) belongs to the cucumber genus of the Cucurbitaceae family, and the selection of cultivars with minimal or no lateral branches can enhance the cultivation management efficiency. The growth of lateral branches is inhibited by strigolactone. To investigate the regulatory mechanism of strigolactone on the lateral branch development in cucumber, the cultivar LZ1 exhibiting multiple lateral branches was selected as the experimental material. The axillae of the plants were infiltrated with 1, 5, and 10 μmol·L−1 germination releaser 24 (GR24) at the four- to five-leaf stage. It was identified that 1 μmol·L−1 GR24 exhibited the most potent inhibitory effect on cucumber lateral branches. Additionally, exogenous strigolactone decreased the auxin content in the apical bud and axillae and increased the auxin content in the stem. This inhibited polar auxin transport in the axillary bud and promoted polar auxin transport in the apical bud. The content of strigolactone in the axilla region of cucumbers was elevated, whereas the synthesis and expression of cytokinin in the same area were reduced. A low concentration of GR24 induced the expression of cucumber branched 1 (csbrc1), whereas a high concentration of GR24 downregulated the expression of cucumber lateral suppressor (cscls) and blind (csblind), which inhibited the growth of cucumber lateral branches.