Effects of Dietary Oxidized Phytosterol on Lipid Metabolism in Rats.

Many in vitro studies have revealed the toxic effects of oxidized phytosterols (OPSs); however, their effects on lipid metabolism are not well understood in vivo. Therefore, we examined the bioavailability of OPS and compared the effects of dietary phytosterols (PSs) or OPS on lipid metabolism in rats. OPS was detected in the plasma and liver of rats administered 50 mg of OPS for 3 days. Rats were fed the AIN76 diet (C group), basal diet plus 0.25% PS (P group), or 0.25% OPS (O group) for 4 weeks. Dietary OPS but not PS reduced hepatic fatty acid synthase activity. Liver triacylglycerol (TG) levels tended to be lower in the P group than in the C group and were significantly lower in the O group. The mRNA expression level of HMG-CoA reductase in the liver was the lowest in the O group, whereas that of CYP27A1 was the highest in the O group. The mRNA expression levels of NPC1L1 in the intestinal mucosa were significantly lower in the P and O groups than in the C group. Consistent with these modulations, plasma total cholesterol (TC) and HDL-C levels were similar between the C and P groups but tended to be higher or significantly higher in the O group. Liver TC levels were significantly lower in the P and O groups than in the C group. Moreover, fecal neutral and acidic steroid levels were the highest in the O group. The mRNA expression level of Δ6 desaturase in the liver was significantly higher in both the P and the O groups than in the C group. The Δ6 desaturation indices of fatty acids in the total liver lipids were the highest in the O group. Thus, dietary OPS may modulate lipid metabolism in the liver.

Excess copper promotes an increase in the concentration of metabolites in Tridax procumbens L.

The study investigated the effects of cultivating Tridax procumbens in hydroponic conditions with different concentrations of copper ions, aiming to understand the physiological changes and the impact on the biosynthesis of secondary metabolites. The treatments consisted of a completely randomized design, with five increasing concentrations of copper (T0 = 0.235, T1 = 12.5, T2 = 25, T3 = 50, T4 = 100 µmol L-1 of Cu), under controlled conditions for 36 days. Analysis of bioactive compounds in leaves was performed by HPLC-DAD and ESI-MS. Several phenolic compounds, alkaloids, phytosterols and triterpenoids were identified, demonstrating the plant's metabolic plasticity. The highest dose of copper (100 µmol L-1) significantly promoted voacangine, the most predominant compound in the analyses. Notably, 66.7% of the metabolites that showed an increase in concentration, were phenolic compounds. Furthermore, treatments with 12.5 and 25 µmol L-1 of copper were identified as promoting the biosynthesis of phytosterols and triterpenoids. These biochemical adaptations can play a fundamental role in the survival and development of plants in environments contaminated by metals, and from this it is possible to determine cultivation techniques that maximize the biosynthesis of the compound of interest.

Lipolysis and Sterol Stability and Bioaccessibility of Wholemeal Rye Bread Enriched with Plant Sterols Subjected to Adult and Elderly Digestion Conditions.

This study evaluated the impact of different digestion conditions (adult and senior) on lipolysis and bioaccessibility of plant sterols (PS) and phytosterol oxidation products (POPs) in PS-enriched wholemeal rye bread. Under adult digestion conditions, the addition of gastric lipase (GL) reduced lipolysis products (by 6.1% for free fatty acids and 11.7% for monoacylglycerols) and the bioaccessibility of PS by 6.7%, compared to the control. In digestion with both GL and cholesterol esterase (CE), these reductions were 12.9, 20.1, and 11.3%, respectively. Both modifications (GL and GL + CE) increased the bioaccessibility of POPs by 4.5-4.0%. When simulating the elderly digestion, the modified gastric and intestinal phases did not alter PS bioaccessibility but decreased POPs bioaccessibility by 21.8% compared to control, along with reduced lipolysis. Incorporating GL and CE thus approached physiological conditions and influenced lipid digestion. Elderly simulated digestion conditions resulted in a positive outcome by maintaining PS bioaccessibility while reducing potentially harmful POPs.

Human Oral Phase Coupled with In Vitro Dynamic Gastrointestinal Digestion for Assessment of Plant Sterol Bioaccessibility from Wholemeal Rye Bread.

A dynamic gastrointestinal digestion system (simgi) after a human oral phase was used, for the first time, to assess the bioaccessibility of plant sterols (PS) from wholemeal rye bread (74.8 ± 2.2 mg of PS/100 g d.m.) and PS-enriched wholemeal rye bread (PS-WRB) (1.6 ± 0.04 g of PS/100 g of fresh bread). The use of these solid food matrices requires a novel adaptation of the gastric phase of the system. The PS identified in the breads are campesterol, campestanol, stigmasterol, ß-sitosterol, sitostanol, Δ5-avenasterol, Δ5,24-stigmastadienol, Δ7-stigmastenol, and Δ7-avenasterol. The bioaccessibility of the total PS, only quantifiable in PS-WRB, is 19.9%, with Δ7-avenasterol being the most bioaccessible and Δ5-avenasterol being the least (p < 0.05). As shown in this study, PS-WRB can be considered to be a good choice to include in the daily diet. Furthermore, although the use of dynamic digestion methods for evaluating bioaccessibility implies high costs and technical complexity, their application means a closer approximation to in vivo scenarios.

Additional mechanism for selective absorption of cholesterol and phytosterols.

Phytosterols are structurally similar to cholesterol but they are much less absorbed (<2%) than cholesterol (>50%) in the intestine. We hypothesize that phytosterols are poor substrates of intestinal acyl-CoA: cholesterol acyltransferase 2 (ACAT2), and thus minimal phytosterol esters are formed and packed into chylomicrons, leading to their low absorption. Two isotope tracing models, including a radioactive hamster microsomal ACAT2 reaction model and a differentiated Caco-2 cell model, were established to examine the specificity of ACAT2 to various sterols, including cholesterol, sitosterol, stigmasterol, and campesterol. Both models consistently demonstrated that only cholesterol but not phytosterols could be efficiently esterified by ACAT2 in a time- and dose-dependent manner. Molecular docking further suggested that unfavorable interactions existed between ACAT2 and phytosterols. In conclusion, phytosterols are poor substrates of ACAT2 and thus minimally absorbed. This work provides a theoretical basis for the use of phytosterol-based supplements in treating dyslipidemia and preventing heart diseases.

The Effect of Whey Protein Isolate Hydrolysate on Digestive Properties of Phytosterol.

Phytosterol (PS) is a steroid, and its bioavailability can be enhanced by interacting with protein in the C-24 hydroxyl group. The interaction between sterols and amino acid residues in proteins can be enhanced by enzymatic hydrolysis. Phytosterol and whey insulation hydrolysates (WPH1-4) fabricated by the Alcalase enzyme at different enzymatic hydrolysis times were selected as delivery systems to simulate sterol C-24 hydroxyl group interaction with protein. Increasing hydrolysis time can promote the production of ß-Lg, which raises the ratio of ß-turn in the secondary structure and promotes the formation of interaction between WPH and PS. The correlation coefficient between hydrogen bonds and encapsulation efficiency (EE) and bioaccessibility is 0.91 and 0.88 (P < 0.05), respectively, indicating that hydrogen bonds of two components significantly influenced the combination by concealing the hydrophobic amino acids and some residues, which improved PS EE and bioavailability by 3.03 and 2.84 times after PS was combined with the WPI hydrolysate. These findings are expected to enhance the absorption of PS and other macromolecules by protein enzymatic hydrolysis to broaden their applications for food.

Sterols, pleiotropic players in plant-microbe interactions.

Plant-microbe interactions (PMIs) are regulated through a wide range of mechanisms in which sterols from plants and microbes are involved in numerous ways, including recognition, transduction, communication, and/or exchanges between partners. Phytosterol equilibrium is regulated by PMIs through expression of genes involved in phytosterol biosynthesis, together with their accumulation. As such, PMI outcomes also include plasma membrane (PM) functionalization events, in which phytosterols have a central role, and activation of sterol-interacting proteins involved in cell signaling. In spite (or perhaps because) of such multifaceted abilities, an overall mechanism of sterol contribution is difficult to determine. However, promising approaches exploring sterol diversity, their contribution to PMI outcomes, and their localization would help us to decipher their crucial role in PMIs.

Octadecyl and sulfonyl modification of diatomite synergistically improved the immobilization efficiency of lipase and its application in the synthesis of pine sterol esters.

Phytosterols usually have to be esterified to various phytosterol esters to avoid their disadvantages of unsatisfactory solubility and low bioavailability. The enzymatic synthesis of phytosterol esters in a solvent-free system has advantages in terms of environmental friendliness, sustainability, and selectivity. However, the limitation of the low stability and recyclability of the lipase in the solvent-free system, which often requires a relatively high temperature to induce the viscosity, also increased the industrial production cost. In this context, a low-cost material, namely diatomite, was employed as the support in the immobilization of Candida rugosa lipase (CRL) due to its multiple modification sites. The Fe3 O4 was also then introduced to this system for quick and simple separation via the magnetic field. Moreover, to further enhance the immobilization efficiency of diatomite, a modification strategy which involved the octadecyl and sulfonyl group for regulating the hydrophobicity and interaction between the support and lipase was successfully developed. The optimization of the ratio of the modifiers suggested that the -SO3 H/C18 (1:1.5) performed best with an enzyme loading and enzyme activity of 84.8 mg·g-1 and 54 U·g-1 , respectively. Compared with free CRL, the thermal and storage stability of CRL@OSMD was significantly improved, which lays the foundation for the catalytic synthesis of phytosterol esters in solvent-free systems. Fortunately, a yield of 95.0% was achieved after optimizing the reaction conditions, and a yield of 70.0% can still be maintained after six cycles.

A SCYL2 gene from Oryza sativa is involved in phytosterol accumulation and regulates plant growth and salt stress.

Rice is a crucial food for humans due to its high nutritional value. Phytosterols, essential components of the plant membrane lipid bilayer, play a vital role in plant growth and contribute significantly to lipid-lowering, antitumor, and immunomodulation processes. In this study, SCY1-like protein kinases 2 (SCYL2) was found to be closely related to the accumulation of phytosterols. The levels of campesterol, stigmasterol, and ß-sitosterol significantly increased in transgenic rice seeds, husks, and leaves, whereas there was a considerable reduction in scyl2 plants. Subsequent investigations revealed the crucial role of SCYL2 in plant development. Mutations in this gene led to stunted plant growth while overexpressing OsSCYL2 in Arabidopsis and rice resulted in larger leaves, taller plants, and accelerated development. When subjected to salt stress, Arabidopsis plants overexpressed OsSCYL2 showed significantly higher germination rates than wild-type plants. Similarly, transgenic rice seedlings displayed better growth than both ZH11 and mutant plants, exhibiting lower malondialdehyde (MDA) content and higher peroxidase (POD), and catalase (CAT) activities. Conversely, scyl2 plants exhibited more yellow leaves or even death. These findings suggested that OsSCYL2 proteins might be involved in phytosterols synthesis and play an important role during plant growth and development. This study provides a theoretical basis for developing functional rice.

Solving the Jigsaw puzzle of phytosterol diversity by a novel sterol methyltransferase from Zea mays.

Phytosterols are vital structural and regulatory components in plants. Zea mays produces a series of phytosterols that are specific to corn. However, the underline biosynthetic mechanism remains elusive. In this study, we identified a novel sterol methyltransferase from Z. mays (ZmSMT1-2) which showed a unique feature compared with documented plant SMTs. ZmSMT1-2 showed a substrate preference for cycloartenol. Using S-adenosyl-L-methionine (AdoMet) as a donor, ZmSMT1-2 converted cycloartenol into alkylated sterols with unique side-chain architectures, including Δ25(27) (i.e., cyclolaudenol and cycloneolitsol) and Δ24(25) (i.e., cyclobranol) sterols. Cycloneolitsol is identified as a product of SMTs for the first time. Our discovery provides a previously untapped mechanism for phytosterol biosynthesis and adds another layer of diversity of sterol biosynthesis.

Differential regulation of key triterpene synthase gene under abiotic stress in Withania somnifera L. Dunal and its co-relation to sterols and withanolides.

Withania somnifera (Ashwagandha), is one of the most reputed Indian medicinal plants, having immense pharmacological activities due to the occurrence of withanolides. The withanolides are biosynthesized through triterpenoid biosynthetic pathway with the involvement of WsCAS leading to cyclization of 2, 3 oxidosqualene, which is a key metabolite to further diversify to a myriad of phytochemicals. In contrast to the available reports on the studies of WsCAS in withanolide biosynthesis, its involvement in phytosterol biosynthesis needs investigation. Present work deals with the understanding of role of WsCAS triterpenoid synthase gene in the regulation of biosynthesis of phytosterols & withanolides. Docking studies of WsCAS protein revealed Conserved amino acids, DCATE motif, and QW motif which are involved in efficient substrate binding, structure stabilization, and catalytic activity. Overexpression/silencing of WsCAS leading to increment/decline of phytosterols confers its stringent regulation in phytosterols biosynthesis. Differential regulation of WsCAS on the metabolic flux towards phytosterols and withanolide biosynthesis was observed under abiotic stress conditions. The preferential channelization of 2, 3 oxidosqualene towards withanolides and/or phytosterols occurred under heat/salt stress and cold/water stress, respectively. Stigmasterol and ß-sitosterol showed major contribution in high/low temperature and salt stress, and campesterol in water stress management. Overexpression of WsCAS in Arabidopsis thaliana led to the increment in phytosterols in general. Thus, the WsCAS plays important regulatory role in the biosynthetic pathway of phytosterols and withanolides under abiotic stress conditions.

Novel sterol binding domains in bacteria.

Sterol lipids are widely present in eukaryotes and play essential roles in signaling and modulating membrane fluidity. Although rare, some bacteria also produce sterols, but their function in bacteria is not known. Moreover, many more species, including pathogens and commensal microbes, acquire or modify sterols from eukaryotic hosts through poorly understood molecular mechanisms. The aerobic methanotroph Methylococcus capsulatus was the first bacterium shown to synthesize sterols, producing a mixture of C-4 methylated sterols that are distinct from those observed in eukaryotes. C-4 methylated sterols are synthesized in the cytosol and localized to the outer membrane, suggesting that a bacterial sterol transport machinery exists. Until now, the identity of such machinery remained a mystery. In this study, we identified three novel proteins that may be the first examples of transporters for bacterial sterol lipids. The proteins, which all belong to well-studied families of bacterial metabolite transporters, are predicted to reside in the inner membrane, periplasm, and outer membrane of M. capsulatus, and may work as a conduit to move modified sterols to the outer membrane. Quantitative analysis of ligand binding revealed their remarkable specificity for 4-methylsterols, and crystallographic structures coupled with docking and molecular dynamics simulations revealed the structural bases for substrate binding by two of the putative transporters. Their striking structural divergence from eukaryotic sterol transporters signals that they form a distinct sterol transport system within the bacterial domain. Finally, bioinformatics revealed the widespread presence of similar transporters in bacterial genomes, including in some pathogens that use host sterol lipids to construct their cell envelopes. The unique folds of these bacterial sterol binding proteins should now guide the discovery of other proteins that handle this essential metabolite.

Phytosterol intake and risk of coronary artery disease: Results from 3 prospective cohort studies.

BACKGROUND: Phytosterols are structurally similar to cholesterol and partially inhibit intestinal absorption of cholesterol, although their impact on coronary artery disease (CAD) risk remains to be elucidated. OBJECTIVES: This study aimed to prospectively assess the associations between total and individual phytosterol intake and CAD risk in United States health professionals. METHODS: The analysis included 213,992 participants from 3 prospective cohorts-the Nurses' Health Study (NHS), NHSII, and Health Professionals Follow-Up Study-without cardiovascular disease or cancer at baseline. Diet was assessed using a validated food frequency questionnaire every 2-4 y since baseline. Associations between phytosterol intake and the risk of CAD, such as nonfatal myocardial infarction and fatal CAD, were evaluated using Cox proportional hazards regression models. RESULTS: More than 5,517,993 person-years, 8725 cases with CAD were documented. Comparing extreme quintiles, pooled hazard ratios (95% CIs) of CAD were 0.93 (0.86, 1.01; P-trend = 0.16) for total phytosterols, 0.89 (0.82, 0.96; P-trend = 0.05) for campesterol, 0.95 (0.88, 1.02; P-trend = 0.10) for stigmasterol, and 0.92 (0.85, 1.00; P-trend = 0.09) for ß-sitosterol. Nonlinear associations were observed for total phytosterols, campesterol, and ß-sitosterol: the risk reduction plateaued at intakes above ∼180, 30, and 130 mg/d, respectively (P-nonlinearity < 0.001). In a subset of participants (N range between 11,983 and 22,039), phytosterol intake was inversely associated with plasma concentrations of total cholesterol, triglycerides, high-density lipoprotein cholesterol, and IL-6 and positively associated with adiponectin, whereas no significant associations were observed for low-density lipoprotein cholesterol or C-reactive protein concentrations. CONCLUSIONS: Higher long-term intake of total and major subtypes of phytosterols may be associated with a modest reduction in CAD risk, displaying a nonlinear relationship that plateau at moderate intake levels. The role of phytosterols in preventing CAD warrants further investigation.

Immobilization of rough morphotype Mycolicibacterium neoaurum R for androstadienedione production.

OBJECTIVES: Enhance the androstadienedione (Androst-1,4-diene-3,17-dione, ADD) production of rough morphotype Mycolicibacterium neoaurum R by repeated-batch fermentation of immobilized cells. RESULTS: M. neoaurum R was a rough colony morphotype variant, obtained from the routine plating of smooth M. neoaurum strain CICC 21097. M. neoaurum R showed rougher cell surface and aggregated in broth. The ADD production of M. neoaurum R was notably lower than that of M. neoaurum CICC 21097 during the free cell fermentation, but the yield gap could be erased after proper cell immobilization. Subsequently, repeated-batch fermentation of immobilized M. neoaurum R was performed to shorten the production cycle and enhance the bio-production efficiency of ADD. Through the optimization of the immobilization carriers and the co-solvents for phytosterols, the ADD productivity of M. neoaurum R immobilized by semi-expanded perlite reached 0.075 g/L/h during the repeated-batch fermentation for 40 days. CONCLUSIONS: The ADD production of the rough-type M. neoaurum R was notably enhanced by the immobilization onto semi-expanded perlite. Moreover, the ADD batch yields of M. neoaurum R immobilized by semi-expanded perlite were maintained at high levels during the repeated-batch fermentation.

Enhancing production and purity of 9-OH-AD from phytosterols by balancing metabolic flux of the side-chain degradation and 9-position hydroxylation in Mycobacterium neoaurum.

9α-Hydroxyandroster-4-ene-3,17-dione (9-OH-AD) is a representative steroid drug intermediate that can be prepared by phytosterols (PS) biotransformation with mycobacteria in a resting cell-cyclodextrin system. In this study, over-expression of 17ß-hydroxysteroid dehydrogenase (Hsd4A) was testified to enhance the side-chain degradation of PS and to reduce the incomplete degradation by-products. Meanwhile, the complete degradation product 4-androstene-3,17-dione (AD) was increased due to the lack of 3-Ketosteroid 9α-Hydroxylase (KshA1) activities. To increase the production and purity of 9-OH-AD, the metabolic pathway of the side-chain degradation of PS and 9-position hydroxylation was modulated by balancing the over-expression of Hsd4A and KshA1 in mycobacteria and reducing the bioconversion rate via lowering the ratio of PS and cyclodextrin. The production and purity of 9-OH-AD in broth were improved from 22.18 g L-1 and 77.13% to 28.27 g L-1 and 87.84%, with a molar yield of 78.32%.

Current and New Insights on Delivery Systems for Plant Sterols in Food.

Plant sterols are minor bioactive components of food lipids, which are often used for the formulation of functional foods due to their cholesterol-lowering properties. However, they have low solubility and tend to crystallize, which may affect their biological effects, the sensory profile of the sterol-enriched food, and its consumer acceptability. Moreover, due to the unsaturated structure of sterols, they are susceptible to oxidation, so different encapsulation systems have been developed to improve their dispersibility/solubility, stability, delivery, and bioaccessibility. This chapter provides an overview of the main encapsulation systems currently used for plant sterols and their application in model and food systems, with a particular focus on their efficiency and impact on sterol bioaccessibility.

Deciphering the effect of salinity and boron stress on broccoli plants reveals that membranes phytosterols and PIP aquaporins facilitate stress adaptation.

Abiotic stresses, such as salinity and boron toxicity/deficiency, are prevalent in arid and semi-arid regions where broccoli is largely cultivated. This study aimed to investigate the physiological response of broccoli leaves to these stresses, focusing on parameters such as growth, relative water content, stomatal conductance, and mineral concentration after 15 days of treatment application. The effects of individual and combined stresses of salinity and boron (deficiency and toxicity) were examined. Additionally, the study explored the molecular aspects of PIP aquaporins in relation to their presence in the plasma membrane and their interaction with the lipid environment. The results showed that the combined stress of salinity and boron deficiency resulted in a significant reduction in plant biomass, suggesting a specific adaptation to this stress combination. Changes in stomatal conductance and mineral nutrient levels indicated that the adaptation mechanisms were associated with water and boron concentration in the leaves. The expression patterns of PIP aquaporins varied among the different stress treatments, either individually or in combination. Furthermore, the presence of aquaporins in the plasma membrane and microsomal fraction highlighted the potential regulatory roles of trafficking along with the membrane composition, particularly the concentration of phytosterols. The results underscore the importance of water transport by aquaporins and their interaction with the sterol composition in the membranes, in facilitating salinity-boron stress adaptation mechanisms.

Surfactin and Capric Acid Affect the Posaconazole Susceptibility of Candida albicans Strains with Altered Sterols and Sphingolipids Biosynthesis.

Infections caused by Candida spp. pose a continuing challenge for modern medicine, due to widespread resistance to commonly used antifungal agents (e.g., azoles). Thus, there is considerable interest in discovering new, natural compounds that can be used in combination therapy with conventional antibiotics. Here, we investigate whether the natural compounds surfactin and capric acid, in combination with posaconazole, enhance the growth inhibition of C. albicans strains with alterations in sterols and the sphingolipids biosynthesis pathway. We demonstrate that combinations of posaconazole with surfactin or capric acid correspond with the decreased growth of C. albicans strains. Moreover, surfactin and capric acid can independently contribute to the reduced adhesion of C. albicans strains with altered ergosterol biosynthesis to abiotic surfaces (up to 90% reduction in adhesion). A microscopic study of the C. albicans plasma membrane revealed that combinations of those compounds do not correspond with the increased permeabilization of the plasma membrane when compared to cells treated with posaconazole alone. This suggests that the fungistatic effect of posaconazole in combination with surfactin or capric acid is related to the reduction in adhesion of C. albicans.

Phytosterol-mediated glycerosomes combined with peppermint oil enhance transdermal delivery of lappaconitine by modulating the lipid composition of the stratum corneum.

Although the introduction of glycerosomes has enriched strategies for efficient transdermal drug delivery, the inclusion of cholesterol as a membrane stabilizer has limited their clinical application. The current study describes the development and optimization of a new type of glycerosome (S-glycerosome) that is formed in glycerol solution with ß-sitosterol as the stabilizer. Moreover, the transdermal permeation properties of lappaconitine (LA)-loaded S-glycerosomes and peppermint oil (PO)-mediated S-glycerosomes (PO-S-glycerosomes) are evaluated, and the lipid alterations in the stratum corneum are analyzed via lipidomics. The LA-loaded S-glycerosomes prepared by the preferred formulation from the uniform design have a mean size of 145.3 ± 7.81 nm and an encapsulation efficiency of 73.14 ± 0.35%. Moreover, the addition of PO positively impacts transdermal flux, peaking at 0.4% (w/v) PO. Tracing of the fluorescent probe P4 further revealed that PO-S-glycerosomes penetrate deeper into the skin than S-glycerosomes and conventional liposomes. Additionally, treatment with PO-S-glycerosomes alters the isoform type, number, and composition of sphingolipids, glycerophospholipids, glycerolipids, and fatty acids in the stratum corneum, with the most notable effect observed for ceramides, the main component of sphingolipids. Furthermore, the transdermal administration of LA-loaded PO-S-glycerosomes improved the treatment efficacy of xylene-induced inflammation in mice without skin irritation. Collectively, these findings demonstrate the feasibility of ß-sitosterol as a stabilizer in glycerosomes. Additionally, the inclusion of PO improves the transdermal permeation of S-glycerosomes, potentially by altering the stratum corneum lipids.

Scaffold protein RACK1 regulates BR signaling by modulating the nuclear localization of BZR1.

Brassinosteroids (BRs) are a group of plant-specific steroid hormones, which induces the rapid nuclear localization of the positive transcriptional factors BRASSINAZOLE RESISTANT1/2 (BZR1/2). However, the mechanisms underlying the regulation of nucleocytoplasmic shuttling of BZR1 remain to be fully elucidated. In this study, we show that the scaffold protein Receptor for Activated C Kinase 1 (RACK1) from Arabidopsis is involved in BR signaling cascades through mediating the nuclear localization of BZR1, which is tightly retained in the cytosol by the conserved scaffold protein 14-3-3s. RACK1 can interact with BZR1 and competitively decrease the 14-3-3 interaction with BZR1 in cytosol, which efficiently enhances the nuclear localization of BZR1. 14-3-3 also retains RACK1 in cytosol through their interaction. Conversely, BR treatment enhances the nuclear localization of BZR1 by disrupting the 14-3-3 interaction with RACK1 and BZR1. Our study uncovers a new mechanism that integrates two kinds of conserved scaffold proteins (RACK1 and 14-3-3) coordinating BR signaling event.