Strigolactone Analogue Research Articles

KARRIKIN INSENSITIVE2 regulates leaf development, root system architecture and arbuscular-mycorrhizal symbiosis in Brachypodium distachyon.

KARRIKIN INSENSITIVE2 (KAI2) is an α/β-hydrolase required for plant responses to karrikins, which are abiotic butenolides that can influence seed germination and seedling growth. Although represented by four angiosperm species, loss-of-function kai2 mutants are phenotypically inconsistent and incompletely characterised, resulting in uncertainties about the core functions of KAI2 in plant development. Here we characterised the developmental functions of KAI2 in the grass Brachypodium distachyon using molecular, physiological and biochemical approaches. Bdkai2 mutants exhibit increased internode elongation and reduced leaf chlorophyll levels, but only a modest increase in water loss from detached leaves. Bdkai2 shows increased numbers of lateral roots and reduced root hair growth, and fails to support normal root colonisation by arbuscular-mycorrhizal (AM) fungi. The karrikins KAR1 and KAR2 , and the strigolactone (SL) analogue rac-GR24, each elicit overlapping but distinct changes to the shoot transcriptome via BdKAI2. Finally, we show that BdKAI2 exhibits a clear ligand preference for desmethyl butenolides and weak responses to methyl-substituted SL analogues such as GR24. Our findings suggest that KAI2 has multiple roles in shoot development, root system development and transcriptional regulation in grasses. Although KAI2-dependent AM symbiosis is likely conserved within monocots, the magnitude of the effect of KAI2 on water relations may vary across angiosperms.

Quercetin and 1-methyl-2-oxindole mimic root signaling that promotes spore germination and mycelial growth of Gigaspora margarita.

Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs, and the difficulty of growing them in asymbiotic or monoxenic (AMF + root) conditions limits research and their large-scale production as biofertilizer. We hypothesized that a combination of flavanols and strigolactones can mimic complex root signaling during the presymbiotic stages of AMF. We evaluated the germination, mycelial growth, branching, and auxiliary cell clusters formation by Gigaspora margarita during the presymbiotic stage in the presence (or absence) of transformed Cichorium intybus roots in basal culture medium enriched with glucose, a flavonol (quercetin or biochanin A) and a strigolactone analogue (1-Methyl-2-oxindole or indole propionic acid). With quercetin (5µM), methyl oxindole (2.5nM), and glucose (8.2g/L) in the absence of roots, the presymbiotic mycelium of G. margarita grew without cytoplasmic retraction and produced auxiliary cells over 71days similar to presymbiotic mycelium in the presence of roots but without glucose, strigolactones, and flavonols. Our results indicate that glucose and a specific combination of certain concentrations of a flavonol and a strigolactone might be used in asymbiotic or monoxenic liquid or semisolid cultures to stimulate AMF inoculant bioprocesses.

Exogenous strigolactones alleviate the photosynthetic inhibition and oxidative damage of cucumber seedlings under salt stress

Strigolactones (SLs) play crucial roles in plant growth and development and during the response to multiple biotic and abiotic stresses. In this study, we investigated the role of exogenous SLs analog GR24 in amelioration of salt damage and analyzed the interaction between GR24 and other signaling molecules in cucumber seedlings under salt stress by using physiological, biochemical and RNA-seq analysis approaches. Higher chlorophyll contents, stomatal conductance, greater efficiency of photosynthetic were observed in GR24-pretreated plants than in non- GR24-pretreated plants under salt stress. In addition, exogenous GR24 pretreatment can also alleviate salt-induced photodamage, enhance the efficiency of ascorbate-glutathione (AsA-GSH) cycle, and scavenge excessive reactive oxygen species (ROS), thus alleviating oxidative stress under salt stress in cucumber. RNA-seq analysis revealed that there were 1678 differentially expressed genes (DEGs) in D (NaCl)_vs_LD (GR24+NaCl), including 1219 up-regulated genes and 459 down-regulated genes. There were 66 DEGs related to photosynthesis, MAPK cascade pathways, oxidation and antioxidant system screened by GO classification and KEGG enrichment analysis, and the expression levels of these genes were consistent with the changes of physiological parameters. However, the effects of GR24 on the photosynthetic of cucumber seedlings under salt stress, as well as the expression levels of MAPK3/4/6 genes were significantly inhibited by diphenyleneiodonium chloride (DPI, NADPH oxidase inhibitor) or dimethylthiourea (DMTU, H2O2 scavenger). These findings suggested that H2O2 and MAPK cascade pathways might play a positive role in exogenous GR24 alleviating salt stress in cucumber seedlings. In conclusion this study provides insights for further investigating the mechanism of SLs in alleviating adversity stress.

Strigolactone Analogs: Two New Potential Bioactiphores for Glioblastoma

Strigolactones (SLs), carotenoid-derived phytohormones, control the plant response and signaling pathways for stressful conditions. In addition, they impact numerous cellular processes in mammalians and present new scaffolds for various biomedical applications. Recent studies demonstrated that SLs possess potent antitumor activity against several cancer cells. Herein, we sought to elucidate the inhibitory effects of SL analogs on the growth and survival of human brain tumor cell lines. Among four tested SLs, we showed for the first time that two lead bioactiphores, indanone-derived SL and EGO10, can inhibit cancer cell proliferation, induce apoptosis, and induce G1 cell cycle arrest at low concentrations. SL analogs were marked by increased expression of Bax/Caspase-3 genes and downregulation of Bcl-2. In silico studies were conducted to identify drug-likeness, blood–brain barrier penetrating properties, and molecular docking with Bcl-2 protein. Taken together, this study indicates that SLs may be promising antiglioma agents, presenting novel pharmacophores for further preclinical and clinical assessment.

GR24-mediated enhancement of salt tolerance and roles of H2O2 and Ca2+ in regulating this enhancement in cucumber

This study investigated the regulation of the exogenous strigolactone (SL) analog GR24 in enhancing the salt tolerance and the effects of calcium ion (Ca2+) and hydrogen peroxide (H2O2) on GR24's regulation effects in cucumber. The seedlings were sprayed with (1) distilled water (CK), (2) NaCl, (3) GR24, then NaCl, (4) GR24, then H2O2 scavenger, then NaCl, and (5) GR24, then Ca2+ blocker, then NaCl. The second true leaf was selected for biochemical assays. Under the salt stress, the exogenous GR24 maintained the ion balance, increased the activity of antioxidant enzymes, reduced the membrane lipid peroxidation, and increased the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX), accompanied by a decrease in relative conductivity, an increase in the proline content, and elevated gene expression levels of antioxidant enzymes, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, calcium-dependent protein kinases (CDPKs), salt overly sensitive SOS1, CBL-interacting protein kinase 2 (CIPK2), and calcineurin B-like protein 3 (CBL3). Such protective effects triggered by GR24 were attenuated or almost abolished by ethylene glycol tetraacetic acid (EGTA), lanthanum chloride (LaCl3, Ca2+ channel blocker), diphenyleneiodonium (DPI, NADPH oxidase inhibitor), and dimethylthiourea (DMTU, hydroxyl radical scavenger). Our data suggest that exogenous GR24 is highly effective in alleviating salt-induced damages via modulating antioxidant capabilities and improving ionic homeostasis and osmotic balance and that H2O2 and Ca2+ are required for GR24-mediated enhancement of salt tolerance.

Enhancement of Astaxanthin and Fatty Acid Production in Haematococcus pluvialis Using Strigolactone

Improving the production rate of high-value nutraceutical compounds, such as astaxanthin and polyunsaturated fatty acids (PUFAs), is important for the commercialization of Haematococcus pluvialis biorefineries. Here, the effects of a phytohormone, strigolactone analog rac-GR24, on cell growth and astaxanthin and fatty acid biosynthesis in H. pluvialis were investigated. Four concentrations (2, 4, 6, and 8 µM) of rac-GR24 were initially added during 30 days of photoautotrophic cultivation. The addition of rac-GR24 improved cell number density and chlorophyll concentration in H. pluvialis cultures compared to the control; the optimal concentration was 8 µM. Despite a slightly reduced astaxanthin content of 30-d-old cyst cells, the astaxanthin production (26.1 ± 1.7 mg/L) improved by 21% compared to the rac-GR24-free control (21.6 ± 1.5 mg/L), owing to improved biomass production. Notably, at the highest dosage of 8 µM rac-GR24, the total fatty acid content of the treated H. pluvialis cells (899.8 pg/cell) was higher than that of the untreated cells (762.5 pg/cell), resulting in a significant increase in the total fatty acid production (361.6 ± 48.0 mg/L; 61% improvement over the control). The ratio of PUFAs, such as linoleic (C18:2) and linolenic (C18:3) acids, among total fatty acids was high (41.5–44.6% w/w) regardless of the rac-GR24 dose.

The strigolactone receptor D14 targets SMAX1 for degradation in response to GR24 treatment and osmotic stress

The effects of the phytohormone strigolactone (SL) and smoke-derived karrikins (KARs) on plants are generally distinct, despite the fact that they are perceived through very similar mechanisms. The homologous receptors DWARF14 (D14) and KARRIKIN-INSENSITIVE2 (KAI2), together with the F-box protein MORE AXILLARY GROWTH2 (MAX2), mediate SL and KAR responses, respectively, by targeting different SMAX1-LIKE (SMXL) family proteins for degradation. These mechanisms are putatively well-insulated, with D14-MAX2 targeting SMXL6, SMXL7, and SMXL8 and KAI2-MAX2 targeting SMAX1 and SMXL2 in Arabidopsis thaliana. Recent evidence challenges this model. We investigated whether D14 can target SMAX1 and whether this occurs naturally. Genetic analysis indicates that the SL analog GR24 promotes D14-SMAX1 crosstalk. Although D14 shows weaker interactions with SMAX1 than with SMXL2 or SMXL7, D14 mediates GR24-induced degradation of SMAX1 in plants. Osmotic stress triggers SMAX1 degradation, which is protective, through SL biosynthesis and signaling genes. Thus, D14-SMAX1 crosstalk may be beneficial and not simply a vestige of the evolution of the SL pathway.

Observation of few GR24 induced fungal-microalgal pellets performance for higher pollutants removal and biogas quality improvement

Microalgae-based technology has attracted increasing attention in the purification of digestate and biogas, owing to environmental friendliness and economic viability. However, mono-microalgae cultivation cannot efficiently remove pollutants and CO2. In this study, an effective approach was used to simultaneously purify digestate and biogas, focusing on the construction of fungal–microalgal associations, optimization of concentration of strigolactone analogue (GR24), evaluation of the growth and photosynthetic performance of symbionts and purification of digestate and biogas. GR24 concentration of 10−9 M and shaking speed of 160 rpm were found to be favorable for the formation of fungal–microalgal pellets. The highest efficiencies with which chemical oxygen demand, total nitrogen, total phosphorus, and CO2 were eliminated were obtained in the cultivation system of fungus Pleurotus geesteranus and microalgae Chlorella vulgaris, resulting in removal rates of 86.17% ± 7.92%, 87.47% ± 8.14%, 85.21% ± 7.69%, and 72.41% ± 6.37%, respectively. Moreover, Pleurotus geesteranus promoted a significant increase in the biomass of Chlorella vulgaris, and the growth performance and photosynthesis of pellets were found to be consistent with the results of pollutant and CO2 removal efficiencies. Collectively, the findings provide new insights into the simultaneous purification of digestate and biogas by cultivating fungal–microalgal pellets.

Strigolactones: New players in the nitrogen-phosphorus signalling interplay.

Nitrogen (N) and phosphorus (P) are among the most important macronutrients for plant growth and development, and the most widely used as fertilizers. Understanding how plants sense and respond to N and P deficiency is essential to optimize and reduce the use of chemical fertilizers. Strigolactones (SLs) are phytohormones acting as modulators and sensors of plant responses to P deficiency. In the present work, we assess the potential role of SLs in N starvation and in the N-P signalling interplay. Physiological, transcriptional and metabolic responses were analysed in wild-type and SL-deficient tomato plants grown under different P and N regimes, and in plants treated with a short-term pulse of the synthetic SL analogue 2'-epi-GR24. The results evidence that plants prioritize N over P status by affecting SL biosynthesis. We also show that SLs modulate the expression of key regulatory genes of phosphate and nitrate signalling pathways, including the N-P integrators PHO2 and NIGT1/HHO. The results support a key role for SLs as sensors during early plant responses to both N and phosphate starvation and mediating the N-P signalling interplay, indicating that SLs are involved in more physiological processes than so far proposed.

Molecular mechanisms underlying the action of strigolactones involved in grapevine root development by interacting with other phytohormone signaling

Strigolactones (SLs) are vital rhizosphere signals that act as phytohormones modulating plant root growth and development. After treatment for 12 days, the synthetic SLs analog GR24 significantly increased the number and density of fine root. The data indicated that different concentrations of GR24 exerted opposite effects on lateral root (LR) initiation. High concentration (10 μM) of GR24, similar to 10 μM TIS108 (a triazole-type inhibitor of SLs), acted as a positive regulator for LR initiation, whereas the treatment with a low concentration (0.1 μM) of GR24 markedly reduced LR density. In addition, root length and surface area were markedly increased by the treatment with 10 μΜ GR24, compared with those of the controls. In root samples treated with 0.1 μM GR24, 10 μM GR24, and 10 μM TIS108, 4534, 5022, and 3803 differentially expressed genes (DEGs) were identified compared to the control, respectively. The results of RNA-Seq highlighted several DEGs, such as ARF, EBF, ERF, CYCA1, and LOB, which play critical roles in hormone signaling, cell cycle, and root growth and development in grapevines. UPLC-MS analysis further demonstrated that SLs application remarkably altered the levels of endogenous hormones. In particular, indole-3-acetic acid (IAA) content in grapevine roots treated with 10 μΜ TIS108 was approximately 4.78 times higher than that in the control, whereas it was the opposite following the 0.1 μΜ or 10 μΜ GR24 treatment. Our study provides the first comprehensive description of the effect of SLs on grapevine root development caused by interacting with other phytohormone signaling, and lays a solid theoretical basis for using SLs to regulate root growth and development in grapevines.

Strigolactones positively regulate abscisic acid-dependent heat and cold tolerance in tomato

Strigolactones are carotenoid-derived phytohormones that impact plant growth and development in diverse ways. However, the roles of strigolactones in the responses to temperature stresses are largely unknown. Here, we demonstrated that strigolactone biosynthesis is induced in tomato (Solanum lycopersicum) by heat and cold stresses. Compromised strigolactone biosynthesis or signaling negatively affected heat and cold tolerance, while application of the synthetic strigolactone analog GR245DS enhanced heat and cold tolerance. Strigolactone-mediated heat and cold tolerance was associated with the induction of abscisic acid (ABA), heat shock protein 70 (HSP70) accumulation, C-REPEAT BINDING FACTOR 1 (CBF1) transcription, and antioxidant enzyme activity. Importantly, a deficiency in ABA biosynthesis compromised the GR245DS effects on heat and cold stresses and abolished the GR245DS-induced transcription of HSP70, CBF1, and antioxidant-related genes. These results support that strigolactones positively regulate tomato heat and cold tolerance and that they do so at least partially by the induction of CBFs and HSPs and the antioxidant response in an ABA-dependent manner.

Catabolism of strigolactones by a carboxylesterase.

Strigolactones (SLs) are carotenoid-derived plant hormones that control shoot branching and communications between host plants and symbiotic fungi or root parasitic plants. Extensive studies have identified the key components participating in SL biosynthesis and signalling, whereas the catabolism or deactivation of endogenous SLs in planta remains largely unknown. Here, we report that the Arabidopsis carboxylesterase 15 (AtCXE15) and its orthologues function as efficient hydrolases of SLs. We show that overexpression of AtCXE15 promotes shoot branching by dampening SL-inhibited axillary bud outgrowth. We further demonstrate that AtCXE15 could bind and efficiently hydrolyse SLs both in vitro and in planta. We also provide evidence that AtCXE15 is capable of catalysing hydrolysis of diverse SL analogues and that such CXE15-dependent catabolism of SLs is evolutionarily conserved in seed plants. These results disclose a catalytic mechanism underlying homoeostatic regulation of SLs in plants, which also provides a rational approach to spatial-temporally manipulate the endogenous SLs and thus architecture of crops and ornamental plants.

Strigolactones affect the root system architecture of cherry rootstock by mediating hormone signaling pathways

Strigolactones (SLs) are new phytohormones that modulate plant root growth and development. Rootstocks affect horticulturally important traits of cultivars, including tree size, abiotic stress tolerance, and disease resistance. This study focused on understanding the effects of SLs on the transcriptional regulation and root system architecture of cherry rootstock. Here, we examined the morphology and profiled endogenous hormone levels, and transcript levels of key genes from the roots treated with synthetic SLs analog GR24 or SLs inhibitor TIS108. Cherry rootstock plantlets treated with 10 μM TIS108 exhibited fewer adventitious roots (AR). The diameter of AR at 5, 10, and 30 days after 0.1 μM GR24 treatment decreased by 23.8, 23.2, and 11.5 %, respectively, whereas AR diameter was 1.15, 1.15, and 1.16 times higher than that in the control when 10 μM TIS108 was applied, respectively. The LR number in plantlets treated with 10 μM TIS108 reached a maximum of 11.25 for each AR, much higher than those of the control and other treatments at 30 days after treatment (DAT). X-ray micro-CT scanning also showed that the treatment with 10 μM TIS108 markedly induced LR initiation but suppressed LR elongation. Furthermore, 2946, 1536, and 2146 differentially expressed genes (DEGs; p-value < 0.05, |log2Fold Change|> 1) were identified in the root samples treated with 0.1 μM GR24, 10 μM GR24, and 10 μM TIS108, respectively, compared to the control. RNA-Seq findings highlighted several DEGs, such as ARF, PP2C, ERF, LOB, and CYC, which play critical roles in hormone signaling, cell cycle, and root growth and development. UPLC-MS analysis further demonstrated that SLs markedly altered the levels of endogenous hormones in cherry rootstock. In particular, the content of endogenous indole-3-acetic acid (IAA) markedly increased by 64.6, 52.1, and 173.5 % after treatment with 0.1 μM GR24, 10 μM GR24, and 10 μM TIS108, respectively. Overall, our study indicates that SLs affect root system architecture by interacting with other plant hormones, which provides a solid theoretical basis for the effects of SLs on the root system architecture of other woody plants.

Synthesis and Evaluation of New Halogenated GR24 Analogs as Germination Promotors for Orobanche cumana.

Orobanche and Striga are parasitic weeds extremely well adapted to the life cycle of their host plants. They cannot be eliminated by conventional weed control methods. Suicidal germination induced by strigolactones (SLs) analogs is an option to control these weeds. Here, we reported two new halogenated (+)-GR24 analogs, named 7-bromo-GR24 (7BrGR24) and 7-fluoro-GR24 (7FGR24), which were synthesized using commercially available materials following simple steps. Both compounds strongly promoted seed germination of Orobanche cumana. Their EC50 values of 2.3±0.28×10−8M (7BrGR24) and 0.97±0.29×10−8M (7FGR24) were 3- and 5-fold lower, respectively, than those of (+)-GR24 and rac-GR24 (EC50=5.1±1.32–5.3±1.44×10−8; p<0.05). The 7FGR24 was the strongest seed germination promoter tested, with a stimulation percentage of 62.0±9.1% at 1.0×10−8M and 90.9±3.8% at 1.0×10−6M. It showed higher binding affinity (IC50=0.189±0.012μM) for the SL receptor ShHTL7 than (+)-GR24 (IC50=0.248±0.032μM), rac-GR24 (IC50=0.319±0.032μM), and 7BrGR24 (IC50=0.521±0.087μM). Molecular docking experiments indicated that the binding affinity of both halogenated analogs to the strigolactone receptor OsD14 was similar to that of (+)-GR24. Our results indicate that 7FGR24 is a promising agent for the control of parasitic weeds.

The Physcomitrium (Physcomitrella) patens PpKAI2L receptors for strigolactones and related compounds function via MAX2-dependent and -independent pathways.

In angiosperms, the α/β hydrolase DWARF14 (D14), along with the F-box protein MORE AXILLARY GROWTH2 (MAX2), perceives strigolactones (SL) to regulate developmental processes. The key SL biosynthetic enzyme CAROTENOID CLEAVAGE DIOXYGENASE8 (CCD8) is present in the moss Physcomitrium patens, and PpCCD8-derived compounds regulate moss extension. The PpMAX2 homolog is not involved in the SL response, but 13 PpKAI2LIKE (PpKAI2L) genes homologous to the D14 ancestral paralog KARRIKIN INSENSITIVE2 (KAI2) encode candidate SL receptors. In Arabidopsis thaliana, AtKAI2 perceives karrikins and the elusive endogenous KAI2-Ligand (KL). Here, germination assays of the parasitic plant Phelipanche ramosa suggested that PpCCD8-derived compounds are likely noncanonical SLs. (+)-GR24 SL analog is a good mimic for PpCCD8-derived compounds in P. patens, while the effects of its enantiomer (-)-GR24, a KL mimic in angiosperms, are minimal. Interaction and binding assays of seven PpKAI2L proteins pointed to the stereoselectivity toward (-)-GR24 for a single clade of PpKAI2L (eu-KAI2). Enzyme assays highlighted the peculiar behavior of PpKAI2L-H. Phenotypic characterization of Ppkai2l mutants showed that eu-KAI2 genes are not involved in the perception of PpCCD8-derived compounds but act in a PpMAX2-dependent pathway. In contrast, mutations in PpKAI2L-G, and -J genes abolished the response to the (+)-GR24 enantiomer, suggesting that PpKAI2L-G, and -J proteins are receptors for moss SLs.

The Role of Strigolactones in the Regulation of Root System Architecture in Grapevine (Vitis vinifera L.) in Response to Root-Restriction Cultivation.

This study investigated the effects of root-restriction cultivation on the root architecture, endogenous strigolactone (SL) content, and SL-related genes expression in grapevine (Vitis vinifera L.). In addition, we clarified the effects of synthetic SL analog GR24 application on grapevine roots to explore the role of SLs in their development. The results showed that the root architecture changed significantly under root-restriction cultivation. At 40 days after transplantation (DAT), the contents of two types of SLs in roots under root restriction were both significantly lower than that in roots of the control. SL content was significantly positively correlated with the expression levels of VvCCD8 and VvD27, indicating that they play vital roles in SLs synthesis. After GR24 treatment for 20 days, the root length was significantly shorter than in the control. A low concentration (0.1 μM) of GR24 significantly reduced the root diameter and increased the fine-root density, while a high concentration (10 μM) of GR24 significantly reduced the lateral root (LR) length and increased the LR density. Concomitantly, GR24 (0.1 μM) reduced endogenous SL content. After GR24 treatment for 5 days, the total content of two tested SLs was highly positively correlated with the expression levels of VvDAD2, whereas it was highly negatively correlated with VvSMAXL4 at 20 days after GR24 treatment. This study helps to clarify the internal mechanism of root-restriction cultivation affecting the changes in grapevine root architecture, as well as further explore the important role of SLs in the growth of grapevine roots in response to root-restriction treatment.

Contribution of strigolactone in plant physiology, hormonal interaction and abiotic stresses.

Strigolactones (SLs) are carotenoid-derived molecules, which regulate various developmental and adaptation processes in plants. These are engaged in different aspects of growth such as development of root, leaf senescence, shoot branching, etc. Plants grown under nutrient-deficient conditions enhance SL production that facilitates root architecture and symbiosis of arbuscular mycorrhizal fungi, as a result increases nutrient uptake. The crosstalk of SLs with other phytohormones such as auxin, abscisic acid, cytokinin and gibberellins, in response to abiotic stresses indicates that SLs actively contribute to the regulatory systems of plant stress adaptation. In response to different environmental circumstances such as salinity, drought, heat, cold, heavy metals and nutrient deprivation, these SLs get accumulated in plant tissues. Strigolactones regulate multiple hormonal responsive pathways, which aids plants to surmount stressful environmental constraints as well as reduce negative impact on overall productivity of crops. The external application of SL analog GR24 for its higher bioaccumulation can be one of the possible approaches for establishing various abiotic stress tolerances in plants.

The Potential of the Synthetic Strigolactone Analogue GR24 for the Maintenance of Photosynthesis and Yield in Winter Wheat under Drought: Investigations on the Mechanisms of Action and Delivery Modes.

Strigolactones (SLs) have been implicated in many plant biological and physiological processes, including the responses to abiotic stresses such as drought, in concert with other phytohormones. While it is now clear that exogenous SLs may help plants to survive in harsh environmental condition, the best, most effective protocols for treatment have not been defined yet, and the mechanisms of action are far from being fully understood. In the set of experiments reported here, we contrasted two application methods for treatment with a synthetic analog of SL, GR24. A number of morphometric, physiological and biochemical parameters were measured following foliar application of GR24 or application in the residual irrigation water in winter wheat plants under irrigated and drought stress conditions. Depending on the concentration and the method of GR24 application, differentiated photosynthesis and transpiration rate, stomatal conductance, leaf water potential, antioxidant enzyme activities and yield in drought conditions were observed. We present evidence that different methods of GR24 application led to increased photosynthesis and yield under stress by a combination of drought tolerance and escape factors, which should be considered for future research exploring the potential of this new family of bioactive molecules for practical applications.

Strigolactone regulates plant architecture by inhibiting lateral branch growth in Quercus mongolica seedlings

ABSTRACT Mongolian oak (Quercus mongolica) is an important timber species in northeast China, but overdeveloped lateral branches during the seedling stage often result in poor plant architecture and reduce the growth potential. Strigolactones (SLs) were proposed to play an important role in plant architecture by inhibiting the growth of lateral branches; however, there is no knowledge on the strigolactone effects in Mongolian oak. In this study, 0.3, 3, 10, and 30 mg/L of GR24 (analogue of SLs) and 1 mg/L Thidiazuron (TDZ) were applied to Mongolian oak seedlings by the lanolin method. All GR24 treatments significantly reduced the number and biomass of lateral branches; in addition, the length increment of lateral branches was decreased by 3, 10 and 30 mg/L GR24. In addition, the auxin content in lateral branches was significantly increased by the 10 mg/L GR24 treatment, which might be one of the main reasons for the inhibition of lateral branch growth. Increased sucrose content in apex, combined with a decrease of sucrose content in lateral branches, further demonstrated the important role of GR24 in inhibiting lateral branch growth.

Nitrate Modulates Lateral Root Formation by Regulating the Auxin Response and Transport in Rice.

Nitrate () plays a pivotal role in stimulating lateral root (LR) formation and growth in plants. However, the role of in modulating rice LR formation and the signalling pathways involved in this process remain unclear. Phenotypic and genetic analyses of rice were used to explore the role of strigolactones (SLs) and auxin in -modulated LR formation in rice. Compared with ammonium (), stimulated LR initiation due to higher short-term root IAA levels. However, this stimulation vanished after 7 d, and the LR density was reduced, in parallel with the auxin levels. Application of the exogenous auxin α-naphthylacetic acid to -treated rice plants promoted LR initiation to levels similar to those under at 7 d; conversely, the application of the SL analogue GR24 to -treated rice inhibited LR initiation to levels similar to those under supply by reducing the root auxin levels at 10 d. D10 and D14 mutations caused loss of sensitivity of the LR formation response to . The application of and GR24 downregulated the transcription of PIN-FORMED 2 (PIN2), an auxin efflux carrier in roots. LR number and density in pin2 mutant lines were insensitive to treatment. These results indicate that LR formation by affecting the auxin response and transport in rice, with the involvement of SLs.