Strigolactone Analogue Research Articles

Characterization of SUPPRESSOR OF MAX2 1-LIKE (SMXL) Genes in ‘duli’ (Pyrus betulifolia L.) and Expression Analysis of PbSMXLs in Response to Plant Growth Regulators and Salt Stress

SUPPRESSOR OF MAX2 1-LIKE (SMXL) proteins are negative regulators of strigolactone (SL) signal transduction that play an important role in regulating plant branching and responses to abiotic stress. Here, we studied the role of SMXL proteins in pear growth, development, and stress resistance. A total of 18 SMXL members were characterized in ‘duli’. All SMXL members were localized to chloroplasts. Chromosome mapping analysis showed that the members of this family were unevenly distributed on 14 chromosomes. Gene fragment replication analysis showed that there were no tandem repeat genes in PbSMXLs, and 12 pairs of homologous genes were fragment duplications. There were 30 pairs of homologous genes between ‘duli’ and apples, and 17 between ‘duli’ and Arabidopsis thaliana. Analysis of cis-acting elements showed that there was a large number of photo-effector elements, short-effector elements, hormone-responsive elements, and abiotic stress-responsive elements in the promoter sequences of this family. Analysis of enzyme activity and endogenous SL showed that β-carotenoid isomerase (D27), carotenoid cleavage dioxygenase 7 (CCD7), lateral branch oxidoreductase (LBO) levels, and SL content were higher in ‘duli’ roots and leaves compared in the control under exogenous GA3 (gibberellin 3), IAA (indole-3-acetic acid), GR24 (synthetic SL analog), and NaCl. Most SMXL genes in ‘duli’ were highly expressed in branches and axillary lobes, but their expression was low in fruits. qRT-PCR analysis revealed that eight PbSMXL genes were responsive to GA3, PAC (Paclobutrazol), IAA, ABA (abscisic acid), GR24, and Tis108 (SL biosynthesis inhibitor). PbSMXLs responded positively to salt stress. The expression of PbSMXL6 and PbSMXL15 was significantly induced under salt stress. The expression of PbSMXL7, PbSMXL10, and PbSMXL15 was significantly induced by Tis108 treatment. The results of this study enhance our understanding of the role of SMXL genes in the responses to plant growth regulators and salt stress. Our findings will also aid future studies of the functions of SMXL genes in ‘duli’.

Strigolactones Regulate Secondary Metabolism and Nitrogen/Phosphate Signaling in Tea Plants via Transcriptional Reprogramming and Hormonal Interactions.

Strigolactones (SLs) are known to regulate plant architecture formation, nitrogen (N) and phosphorus (P) responses, and secondary metabolism, but their effects in tea plants remain unclear. We demonstrated that the application of a bioactive SL analogue GR24 either to tea roots or leaves initially stimulated but later inhibited catechins, theanine, and caffeine biosynthesis. GR24 treatment also promoted the accumulation of flavonols and insoluble proanthocyanidins in a time- and dose-dependent manner. GR24 influenced flavonoid and theanine biosynthesis genes, such as up-regulating CsTT2c, CsMYB12, and CsbZIP1, modulating N-responsive and assimilation genes (CsNRT1,1, CsGSI/TS1, CsHRS1, CsPHR1, CsNLA1, and CsLBD37/38/39), and repressing N/P transport and signaling genes (CsPHO2, CsPHT1s, CsNRT2,2, CsHHO1, and CsWRKY38). GR24-induced changes in secondary metabolites were also observed in the leaves of tea plants. GR24-regulated CsLBD37a interacted with CsTT8a and CsTT2c, repressing catechins biosynthesis by interrupting MBW complex formation. GR24 regulated caffeine biosynthesis and regulator genes CsS40 and CsNAC7 and may thereby suppress caffeine production. GR24 altered the transcriptomic profiles of multiple hormone biosynthesis and signaling genes that potentially regulate tea characteristic metabolism and N/P signaling. This study provides new insights into SL-induced transcriptional reprogramming that leads to changes in N/P nutrition, secondary metabolism, and hormone signaling in tea plants.

Inhibition of the Germination of Root Parasitic Plants by Zeolitic Imidazolate Framework-8.

Crystalline ZIF-8 (C-ZIF-8) and amorphous ZIF-8 (Am-ZIF-8) were prepared and investigated to control the germination of Striga hermonthica, a root parasitic plant, which threatens cereal crops production particularly in sub-Saharan Africa. We have demonstrated that Am-ZIF-8 shows a better performance than C-ZIF-8 in inhibiting Striga seeds germination. This efficient performance of Am-ZIF-8 materials can be attributed to the incomplete deprotonation of 2 methylimidazole (2MIM) during amorphization, leading to the presence of unsaturated Zn-N coordination with the uncoordinated -NH groups available to undergo hydrogen bonding with the strigolactone analog GR24 forming a more stable Am-ZIF-8⋅⋅⋅GR24 hydrogen bonded network. We further established that application of ZIF-8 materials generally has no adverse effects on the growth and quality of rice crops.

Heading Date 3a Stimulates Tiller Bud Outgrowth in Oryza sativa L. through Strigolactone Signaling Pathway.

Heading date 3a (Hd3a, a FLOWERING LOCUS T (FT) ortholog from rice) is well known for its important role in rice (Oryza sativa L.), controlling floral transition under short-day (SD) conditions. Although the effect of Hd3a on promoting branching has been found, the underlying mechanism remains largely unknown. In this report, we overexpressed an Hd3a and BirAG (encoding a biotin ligase) fusion gene in rice, and found that early flowering and tiller bud outgrowth was promoted in BHd3aOE transgenic plants. On the contrary, knockout of Hd3a delayed flowering and tiller bud outgrowth. By using the BioID method, we identified multiple Hd3a proximal proteins. Among them, D14, D53, TPR1, TPR2, and TPRs are central components of the strigolactone signaling pathway, which has an inhibitory effect on rice tillering. The interaction between Hd3a, on the one hand, and D14 and D53 was further confirmed by the bimolecular fluorescence complementation (BiFC), yeast two-hybrid (Y2H), and co-immunoprecipitation (Co-IP) methods. We also found that Hd3a prevented the degradation of D53 induced by rac-GR24 (a strigolactone analog) in rice protoplasts. RT-qPCR assay showed that the expression levels of genes involved in strigolactone biosynthesis and signal transduction were altered significantly between WT and Hd3a overexpression (Hd3aOE) or mutant (hd3a) plants. OsFC1, a downstream target of the strigolactone signaling transduction pathway in controlling rice tillering, was downregulated significantly in Hd3aOE plants, whereas it was upregulated in hd3a lines. Collectively, these results indicate that Hd3a promotes tiller bud outgrowth in rice by attenuating the negative effect of strigolactone signaling on tillering and highlight a novel molecular network regulating rice tiller outgrowth by Hd3a.

Callose and Salicylic Acid Are Key Determinants of Strigolactone-Mediated Disease Resistance in Arabidopsis

Research has demonstrated that strigolactones (SLs) mediate plant disease resistance; however, the basal mechanism is unclear. Here, we provide key genetic evidence supporting how SLs mediate plant disease resistance. Exogenous application of the SL analog, rac-GR24, increased Arabidopsis thaliana resistance to virulent Pseudomonas syringae. SL-biosynthetic mutants and overexpression lines of more axillary growth 1 (MAX1, an SL-biosynthetic gene) enhanced and reduced bacterial susceptibility, respectively. In addition, rac-GR24 promoted bacterial pattern flg22-induced callose deposition and hydrogen peroxide production. SL-biosynthetic mutants displayed reduced callose deposition but not hydrogen peroxide production under flg22 treatment. Moreover, rac-GR24 did not affect avirulent effector-induced cell death between Col-0 and SL-biosynthetic mutants. Furthermore, rac-GR24 increased the free salicylic acid (SA) content and significantly promoted the expression of pathogenesis-related gene 1 related to SA signaling. Importantly, rac-GR24- and MAX1-induced bacterial resistance disappeared completely in Arabidopsis plants lacking both callose synthase and SA. Taken together, our data revealed that callose and SA are two important determinants in SL-mediated plant disease resistance, at least in Arabidopsis.

Strigolactone enhances tea plant adaptation to drought and Phyllosticta theicola petch by regulating caffeine content via CsbHLH80

Strigolactones (SLs) play crucial roles in both plant growth and stress responses. However, their impact on the secondary metabolites of woody plants remains elusive. Here, we found that exogenous strigolactone analogue GR24 positively regulates tea plant flavor secondary metabolites, concurrently inhibiting caffeine biosynthesis and promoting the accumulation of caffeine catabolic pathway products. In this process, SL directly or indirectly inhibits the expression of CsSAMSs by inducing CsbHLH80, thereby reducing caffeine biosynthesis. Furthermore, CsbHLH80 enhances caffeine degradation, leading to increased allantoin. Under normal conditions, heightened allantoin reduces abscisic acid (ABA) accumulation. This inhibition reverses under drought stress. Increased ABA significantly enhances tea plant tolerance to both drought and Phyllosticta theicola Petch. In summary, this study offers novel insights for improving tea plant adaptation and quality in arid regions, particularly emphasizing the selection of stress-tolerant varieties and the refinement of production measures with a focus on high-quality production and environmentally friendly biological control methods.

Biosynthesis and Signaling of Strigolactones Act Synergistically With That of ABA and JA to Enhance Verticillium dahliae Resistance in Cotton (Gossypium hirsutum L.).

Verticillium wilt (VW) caused by the soil-borne fungal pathogen Verticillium dahliae reduces cotton productivity and quality. Numerous studies have explored the genetic and molecular mechanisms regulating VW resistance in cotton, but the role and mechanism of strigolactone (SL) is still elusive. We investigated the function of SL in cotton's immune response to V. dahliae infection by exogenously applying SL analog, blocking or enhancing biosynthesis of endogenous SLs in combination with comparative transcriptome analysis and by exploring cross-talk between SL and other phytohormones. Silencing GhDWARF27 and applying the SL analog GR24 or overexpressing GhDWARF27 decreased and enhanced V. dahliae resistance, respectively. Transcriptome analysis revealed SL-mediated activation of abscisic acid (ABA) and jasmonic acid (JA) biosynthesis and signaling pathways. Enhanced ABA biosynthesis and signaling led to increased activity of antioxidant enzymes and reduced buildup of excess reactive oxygen species. Enhanced JA biosynthesis and signaling facilitated transcription of JA-dependent disease resistance genes. One of the components of the SL signal transduction pathway, GhD53, was found to interact with GhNCED5 and GhLOX2, the key enzymes of ABA and JA biosynthesis, respectively. We revealed the molecular mechanism underlying SL-enabled V. dahliae resistance and provided potential solutions for improving VW resistance in cotton.

Enhanced disease resistance against Botrytis cinerea by strigolactone-mediated immune priming in Arabidopsis thaliana.

Strigolactones (SLs) are a class of plant hormones that play several roles in plants, such as suppressing shoot branching and promoting arbuscular mycorrhizal symbiosis. The positive regulation of plant disease resistance by SLs has recently been demonstrated by analyses using SL-related mutants. In Arabidopsis, SL-mediated signaling has been reported to modulate salicylic acid-mediated disease resistance, in which the priming of plant immunity plays an important role. In this study, we analyzed the effect of the synthetic SL analogue rac-GR24 on resistance against necrotrophic pathogen Botrytis cinerea. In rac-GR24-treated plants, disease resistance against B. cinerea was enhanced in an ethylene- and camalexin-dependent manners. Expression of the ethylene-related genes and the camalexin biosynthetic gene and camalexin accumulation after pathogen infection were enhanced by immune priming in rac-GR24-treated plants. These suggest that SL-mediated immune priming is effective for many types of resistance mechanisms in plant self-defense systems.

Strigolactones positively regulate HY5-dependent autophagy and the degradation of ubiquitinated proteins in response to cold stress in tomato.

Autophagy, involved in protein degradation and amino acid recycling, plays a key role in plant development and stress responses. However, the relationship between autophagy and phytohormones remains unclear. We used diverse methods, including CRISPR/Cas9, ultra-performance liquid chromatography coupled with tandem mass spectrometry, chromatin immunoprecipitation, electrophoretic mobility shift assays, and dual-luciferase assays to explore the molecular mechanism of strigolactones in regulating autophagy and the degradation of ubiquitinated proteins under cold stress in tomato (Solanum lycopersicum). We show that cold stress induced the accumulation of ubiquitinated proteins. Mutants deficient in strigolactone biosynthesis were more sensitive to cold stress with increased accumulation of ubiquitinated proteins. Conversely, treatment with the synthetic strigolactone analog GR245DS enhanced cold tolerance in tomato, with elevated levels of accumulation of autophagosomes and transcripts of autophagy-related genes (ATGs), and reduced accumulation of ubiquitinated proteins. Meanwhile, cold stress induced the accumulation of ELONGATED HYPOCOTYL 5 (HY5), which was triggered by strigolactones. HY5 further trans-activated ATG18a transcription, resulting in autophagy formation. Mutation of ATG18a compromised strigolactone-induced cold tolerance, leading to decreased formation of autophagosomes and increased accumulation of ubiquitinated proteins. These findings reveal that strigolactones positively regulate autophagy in an HY5-dependent manner and facilitate the degradation of ubiquitinated proteins under cold conditions in tomato.

Resilient mechanism of strigolactone (GR24) in regulating morphological and biochemical status of maize under salt stress

Strigolactones (SLs), relatively recent plant growth regulators, bolster plant resilience in challenging environmental conditions and augment signaling networks. Salinity, a well-established abiotic stressor, threatens global crop cultivation and productivity. We hypothesized that the synthetic SL analogue GR24 could alleviate salinity stress in maize by reducing oxidative damage and enhancing various growth and physiological attributes. To explore this hypothesis, we subjected two maize hybrids, PB-ProA-2018 and PB-ProA-2019, to seed priming with three GR24 concentrations (non-soaked, water-soaked, 0.001, 0.01, 0.1 mg/L) for 16 h. Seeds were then germinated in sand culture under two salt stress levels [ 0 (Control) and 100 mM NaCl] and nourished with Hoagland's nutrient medium. Salt stress significantly stunted maize growth attributes. The pre-soaking seed treatment with 0.01 mg L⁻1 GR24 demonstrated a significant enhancement in plant growth metrics, yielding a 31.3% increase in root length and a 62% augmentation in total leaf area per plant, in comparison to non-soaked yet stressed plants. Salt stress led to increased activities of catalase and peroxidase, along with higher levels of leaf ascorbic acid, malondialdehyde, H₂O₂, glycine betaine, and free proline, compared to control seedlings. Pre-soaking with 0.01 mg L−1 GR24 further upregulated superoxide dismutase (SOD) by 29.6%, peroxidase (POD) by 68.3%, catalase (CAT) by 25%, ascorbic acid by 23.1%, free proline by 42.3%, and total phenolics content by 13%, compared to stressed counterparts. Notably, the 0.01 mg L−1 GR24 concentration exhibited superior efficacy in mitigating salt stress effects, with PB-ProA-2019 outperforming PB-ProA-2018 among the maize hybrids. These findings advance our understanding of SLs' potential in alleviating salinity stress in maize, offering valuable insights for crop resilience enhancement.

Cytokinin catabolism and transport are involved in strigolactone-modulated rice tiller bud elongation fueled by phosphate and nitrogen supply

Phosphate (P) and nitrogen (N) fertilization affect rice tillering, indicating that P- and N-regulated tiller growth has a crucial effect on grain yield. Cytokinins and strigolactones (SLs) promote and inhibit tiller bud outgrowth, respectively; however, the underlying mechanisms are unclear. In this study, tiller bud outgrowth and cytokinin fractions were evaluated in rice plants fertilized at different levels of P and N. Low phosphate or nitrogen (LP or LN) reduced rice tiller numbers and bud elongation, in line with low cytokinin levels in tiller buds and xylem sap as well as low TCSn:GUS expression, a sensitive cytokinin signal reporter, in the stem base. Furthermore, exogenous cytokinin (6-benzylaminopurin, 6-BA) administration restored bud length and TCSn:GUS activity in LP- and LN-treated plants to similar levels as control plants. The TCSn:GUS activity and tiller bud outgrowth were less affected by LP and LN supplies in SL-synthetic and SL-signaling mutants (d17 and d53) compared to LP- and LN-treated wild-type (WT) plants, indicating that SL modulate tiller bud elongation under LP and LN supplies by reducing the cytokinin levels in tiller buds. OsCKX9 (a cytokinin catabolism gene) transcription in buds and roots was induced by LP, LN supplies and by adding the SL analog GR24. A reduced response of cytokinin fractions to LP and LN supplies was observed in tiller buds and xylem sap of the d53 mutant compared to WT plants. These results suggest that cytokinin catabolism and transport are involved in SL-modulated rice tillering fueled by P and N fertilization.

Effects of mixed LED light wavelengths and strigolactone analog concentrations on integral biogas upgrading and antibiotic removal from piggery wastewater by different microalgae-bacteria-fungi consortia

This study investigated the combined effects of mixed LED light wavelengths and varying concentrations of the strigolactone analog (GR24) on methane and antibiotic removal in swine wastewater using different microalgae co-culture techniques. Four treatments were implemented: Treatment 1 involved Chlorella vulgaris monocultures, Treatment 2 included C. vulgaris-activated sludge-Clonostachys rosea (C. rosea), Treatment 3 included C. vulgaris-Bacillus licheniformis-C. rosea, and Treatment 4 included C. vulgaris-S395-2-C. rosea. These treatments were designed to optimize conditions for antibiotic and CO2 removal. Treatment 4 showed the highest growth rate (0.329 ± 0.030 d−1), mean daily productivity (0.166 ± 0.015 g L−1 d−1), CA activity (66.25 ± 5.39), and photosynthesis under a red-to-blue light ratio of 5:5. Significant antibiotic removal rates were achieved: 98.77 ± 1.05 % for tetracycline hydrochloride, 93.74 ± 5.06 % for oxytetracycline hydrochloride, 62.44 ± 5.58 % for ciprofloxacin, 55.07 ± 4.97 % for norfloxacin, 70.39 ± 6.03 % for sulfadimethoxine, and 67.46 ± 6.25 % for sulfamethoxazole. A concentration of 10−9 M GR24 maximally enhanced antibiotic and CO2 removal in Treatment 4. This study provided valuable insights into improving wastewater treatment practices and environmental management.

Performance of four different microalgae-based technologies in antibiotics removal under multiple concentrations of antibiotics and strigolactone analogue GR24 administration

The formation of symbionts by using different combinations of endophytic bacteria, microalgae, and fungi to purify antibiotics-containing wastewater is an effective and promising biomaterial technology. As it enhances the mixed antibiotics removal performance of the bio-system, this technology is currently extensively studied. Using exogenous supplementation of various low concentrations of the phytohormone strigolactone analogue GR24, the removal of various antibiotics from simulated wastewater was examined. The performances of Chlorella vulgaris monoculture, activated sludge–C. vulgaris–Clonostachys rosea, Bacillus licheniformis–C. vulgaris–C. rosea, and endophytic bacteria (S395-2)–C. vulgaris–C. rosea co-culture systems were systematically compared. Their removal capacities for tetracycline, oxytetracycline, and chlortetracycline antibiotics from simulated wastewater were assessed. Chlorella vulgaris–endophytic bacteria–C. rosea co-cultures achieved the best performance under 0.25 mg L−1 antibiotics, which could be further enhanced by GR24 supplementation. This result demonstrates that the combination of endophytic bacteria with microalgae and fungi is superior to activated sludge–B. licheniformis–microalgae–fungi systems. Exogenous supplementation of GR24 is an effective strategy to improve the performance of antibiotics removal from wastewater.

Gene expression controlling signalling molecules within mutualistic associations of an invasive plant: An evolutionary perspective

Abstract Chemical signals are crucial in mediating ecological and evolutionary adaptation of plants to their environments. Indeed, invasive plants may produce greater amounts of chemical metabolites in their new ranges. Some of these chemicals can enhance their mutualistic interactions and improve invasive plant performance, but genetic mechanisms of such adaptations are unexplored. We used Triadica sebifera plants as a model to investigate evolutionary changes in chemical signals that enhance arbuscular mycorrhizal (AM) fungal associations. Previous studies found that T. sebifera plants from invasive populations had higher root exudate concentrations of the flavonoid quercetin and elevated AM fungal colonization compared with those from native populations. Here, we explored genetic variation in strigolactone concentrations in root exudates and their contribution to AM fungal colonization with strigolactone analogue GR24 additions. In addition, we studied how gene expression patterns related to flavonoid and strigolactone biosynthesis varied among invasive and native populations using comparative genomics, transcriptomics and fluorescent real‐time quantitative PCR. We found that plants from invasive populations had higher concentrations of the strigolactone 5‐deoxystrigol in root exudates that were correlated with higher AM fungal colonization rates, relative to those from native populations. Exogenous applications of GR24, a synthetic analogue of 5‐deoxystrigol, increased AM fungal colonization. We found higher expression of a single gene in flavonoid (FLS) and strigolactone (DAD1) biosynthesis pathways increased levels of quercetin and 5‐deoxystrigol in plants from invasive populations, respectively. Synthesis. Understanding the role of genetic evolution in enhancing mutualisms of invasive plants provides new insights into the underlying mechanisms of plant invasion. This study suggests that an invasive plant enhanced its mutualisms by upregulating the expression of key genes related to secondary metabolites in root exudates which stimulate symbiotic relationships with AM fungi. Thus, these findings provide insights into genetic mechanisms that underlie higher AM fungal colonization and enhanced invasive plant performance.

The role of strigolactones in resistance to environmental stress in plants.

Abiotic stress impairs plant growth and development, thereby causing low yield and inferior quality of crops. Increasing studies reported that strigolactones (SL) are plant hormones that enhance plant stress resistance by regulating plant physiological processes and gene expressions. In this review, we introduce the response and regulatory role of SL in salt, drought, light, heat, cold and cadmium stresses in plants. This review also discusses how SL alleviate the damage of abiotic stress in plants, furthermore, introducing the mechanisms of SL enhancing plant stress resistance at the genetic level. Under abiotic stress, the exogenous SL analog GR24 can induce the biosynthesis of SL in plants, and endogenous SL can alleviate the damage caused by abiotic stress. SL enhanced the stress resistance of plants by protecting photosynthesis, enhancing the antioxidant capacity of plants and promoting the symbiosis between plants and arbuscular mycorrhiza (AM). SL interact with abscisic acid (ABA), salicylic acid (SA), auxin, cytokinin (CK), jasmonic acid (JA), hydrogen peroxide (H2O2) and other signal molecules to jointly regulate plant stress resistance. Lastly, both the importance of SL and their challenges for future work are outlined in order to further elucidate the specific mechanisms underlying the roles of SL in plant responses to abiotic stress.

Zaxinone Synthase overexpression modulates rice physiology and metabolism, enhancing nutrient uptake, growth and productivity.

The rice Zaxinone Synthase (ZAS) gene encodes a carotenoid cleavage dioxygenase (CCD) that forms the apocarotenoid growth regulator zaxinone in vitro. Here, we generated and characterized constitutive ZAS-overexpressing rice lines, to better understand ZAS role in determining zaxinone content and regulating growth and architecture. ZAS overexpression enhanced endogenous zaxinone level, promoted root growth and increased the number of productive tillers, leading to about 30% higher grain yield per plant. Hormone analysis revealed a decrease in strigolactone (SL) content, which we confirmed by rescuing the high-tillering phenotype through application of a SL analogue. Metabolomics analysis revealed that ZAS overexpressing plants accumulate higher amounts of monosaccharide sugars, in line with transcriptome analysis. Moreover, transgenic plants showed higher carbon (C) assimilation rate and elevated root phosphate, nitrate and sulphate level, enhancing the tolerance towards low phosphate (Pi). Our study confirms ZAS as an important determinant of rice growth and architecture and shows that ZAS regulates hormone homoeostasis and a combination of physiological processes to promote growth and grain yield, which makes this gene an excellent candidate for sustainable crop improvement.

Understanding the interplay between strigolactone and nitric oxide in alleviating cadmium-induced toxicity in Artemisia annua

Metal stress severely limits the development and productivity of medicinal plants like A. annua. Strigolactone (SL), a relatively new plant hormone, and nitric oxide (NO) have demonstrated potential in mitigating HM-related symptoms in plants. Both SLs and NO are regulatory signals that play different roles under stressful conditions. At the moment, it is unclear how SLs and NO interact in plants under cadmium (Cd) stress. In this study, Artemisia annua was utilized to study the role and interaction of SL and NO for Cd stress tolerance. To investigate this, we undertook a detailed physiological, anatomical, and histochemical examination to determine the mechanisms by which SLs and NO reduce the effects of Cd stress on A. annua plants. Cadmium exposure hindered the growth of A. annua plants, influenced several chlorophyll fluorescence attributes, altered antioxidant enzyme activity, lowered cell viability, and caused lipid peroxidation, oxidative damage, and chloroplast ultrastructure abnormalities. A. annua plants grew better when treated with 4 μM synthetic SL analogue GR24 and 200 μM NO donor sodium nitroprusside. Meanwhile, under Cd stress, GR24 and/or SNP spray effectively boosted chlorophyll and carotenoid content, increased antioxidant enzyme activity, and elevated proline and glutathione levels. Treatment with SNP and/or GR24 improved chloroplast ultrastructure and chlorophyll fluorescence characteristics in plants under Cd-stress, resulting in better photosynthetic performance. It also reduced Cd accumulation, increased membrane permeability, and regulated stomatal behavior, resulting in enhanced stomatal conductance in Cd-stressed plants. The application of these growth regulators to plants under Cd-stress mitigated the decrease in glandular trichome dimensions and artemisinin content as observed from the HPLC results. Our results indicate that GR24 and NO, either individually or in combination, can be very effective in reducing Cd-induced damage in A. annua.

Physiological and transcriptomic analyses provide new insights into the regulatory mechanisms of accelerated senescence of litchi fruit in response to strigolactones

Strigolactones (SLs), a class of plant hormones that are derived from carotenoid metabolism, play pivotal roles in regulating various physiological processes in plants. However, the action mode of SLs in regulating postharvest physiology of fruits is not well understood. This study aimed to explore the effect of exogenous GR24 (a synthetic analogue of SLs) on litchi senescence and its possible mechanisms based on physiological and transcriptomic analyses. The results demonstrated that GR24 treatment at 0.5 μM accelerated the development of pericarp browning and discoloration in litchi fruit during storage at ambient conditions, which was related to exacerbated oxidative stress and aggravated membrane deterioration, as indicated by increased reactive oxygen species production, membrane permeability and malondialdehyde content. Compared to those in the control fruit, lower activities of antioxidant enzyme (superoxide dismutase, catalase, glutathione reductase, ascorbate peroxidase and glutathione peroxidase) and contents of antioxidants (ascorbic acid and reduced glutathione), but higher prooxidant enzyme (peroxidase) activity were observed in GR24-treated fruit. Transcriptomic analysis revealed that GR-24 treatment downregulated the expression of genes associated with antioxidant system, pentose phosphate pathway, oxidative phosphorylation and energy metabolism, which was aligned with the physiological results. These findings provide insights into the role of SLs in regulating senescence of harvested litchi fruit.

A dual regulatory role for the arbuscular mycorrhizal master regulator RAM1 in tomato.

The REQUIRED FOR ARBUSCULAR MYCORRHIZATION1 (RAM1) transcription factor from the GRAS family is well known for its role as a master regulator of the arbuscular mycorrhizal (AM) symbiosis in dicotyledonous and monocotyledonous species, being essential in transcriptional reprogramming for the development and functionality of the arbuscules. In tomato, SlGRAS27 is the putative orthologue of RAM1 (here named SlRAM1), but has not yet been characterized. A reduced colonization of the root and impaired arbuscule formation were observed in SlRAM1-silenced plants, confirming the functional conservation of the RAM1 orthologue in tomato. However, unexpectedly, SlRAM1-overexpressing (UBIL:SlRAM1) plants also showed decreased mycorrhizal colonization. Analysis of non-mycorrhizal UBIL:SlRAM1 roots revealed an overall regulation of AM-related genes and a reduction of strigolactone biosynthesis. Moreover, external application of the strigolactone analogue GR244DO almost completely reversed the negative effects of SlRAM1 overexpression on the frequency of mycorrhization. However, it only partially recovered the pattern of arbuscule distribution observed in control plants. Our results strongly suggest that SlRAM1 has a dual regulatory role during mycorrhization and, in addition to its recognized action as a positive regulator of arbuscule development, it is also involved in different mechanisms for the negative regulation of mycorrhization, including the repression of strigolactone biosynthesis.

The Coupling Effects of PGPR Inoculation and Foliar Spraying of Strigolactone in Mitigating the Negative Effect of Salt Stress in Wheat Plants: Insights from Phytochemical, Growth, and Yield Attributes

Salt stress has detrimental effects on wheat plants at several physiological, biochemical, and molecular levels. This stress leads to suppressed growth, reduced grain yield, and poor quality of harvested grains. However, two approaches have shown promise for improving wheat salt tolerance: using a synthetic strigolactone analog called GR24 and applying plant growth-promoting rhizobacteria (PGPR). GR24 plays a vital role in regulating plant growth and development and in defense against various stresses. Conversely, PGPR are beneficial bacteria that colonize the rhizosphere of plants and promote their growth through multiple mechanisms. In our study, we investigated the effects of salinity on the growth and yield traits of two different wheat cultivars and explored the combined role of PGPR and GR24 in mitigating the impact of salt stress. We created three different salinity levels using NaCl in pots (original, 5 dS m−1, and 10 dS m−1) and inoculated wheat seeds with a salt-tolerant Bacillus velezensis UTB96 strain. In addition, we applied 10 μM GR24 via foliar application during the pollination stage. Our observations showed that salt stress negatively affected wheat’s growth, yield, and phytochemical properties compared to the control. However, both single and combined applications of PGPR and GR24 mitigated the adverse effects of salinity. The combined treatment had a more substantial impact than either alone in inducing and improving biochemical and ionic characteristics. These included decreasing Na+ content in both leaves and roots, and EL, H2O2, and MDA content in leaves while increasing K+ content in both leaves and roots, growth and yield-related traits, RWC, chlorophyll pigments, total protein, soluble sugar, starch, proline, GB, and antioxidant enzyme activity (APX, POX, and CAT) of leaves. In conclusion, integrating PGPR and GR24 can efficiently induce salt tolerance and improve plant growth under stressed conditions. This combined approach has the potential for broad applicability in supporting plant growth in the presence of salt stress.