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At least 73 records · Page 4Linked to original sources
PubMed1997

The Arabidopsis deetiolated2 mutant is blocked early in brassinosteroid biosynthesis.

The Arabidopsis DEETIOLATED2 (DET2) gene has been cloned and shown to encode a protein that shares significant sequence identity with mammalian steroid 5 alpha-reductases. Loss of DET2 function causes many defects in Arabidopsis development that can be rescued by the application of brassinolide; therefore, we propose that DET2 encodes a reductase that acts at the first step of the proposed biosynthetic pathway--in the conversion of campesterol to campestanol. Here, we used biochemical measurements and biological assays to determine the precise biochemical defect in det2 mutants. We show that DET2 actually acts at the second step in brassinolide biosynthesis in the 5 alpha-reduction of (24R)-24-methylcholest-4-en-3-one, which is further modified to form campestanol. In feeding experiments using 2H6-labeled campesterol, no significant level of 2H6-labeled campestanol was detected in det2, whereas the wild type accumulated substantial levels. Using gas chromatography-selected ion monitoring analysis, we show that several presumed null alleles of det2 accumulated only 8 to 15% of the wild-type levels of campestanol. Moreover, in det2 mutants, the endogenous levels of (24R)-24-methylcholest-4-en-3-one increased by threefold, whereas the levels of all other measured brassinosteroids accumulated to < 10% of wild-type levels. Exogenously applied biosynthetic intermediates of brassinolide were found to rescue both the dark- and light-grown defects of det2 mutants. Together, these results refine the original proposed pathway for brassinolide and indicate that mutations in DET2 block the second step in brassinosteroid biosynthesis. These results reinforce the utility of combining genetic and biochemical analyses to studies of biosynthetic pathways and strengthen the argument that brassinosteroids play an essential role in Arabidopsis development.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed2006

Brassinosteroids regulate dissociation of BKI1, a negative regulator of BRI1 signaling, from the plasma membrane.

Brassinosteroids, the steroid hormones of plants, are perceived at the plasma membrane by a leucine-rich repeat receptor serine/threonine kinase called BRI1. We report a BRI1-interacting protein, BKI1, which is a negative regulator of brassinosteroid signaling. Brassinosteroids cause the rapid dissociation of BKI1-yellow fluorescent protein from the plasma membrane in a process that is dependent on BRI1-kinase. BKI1 is a substrate of BRI1 kinase and limits the interaction of BRI1 with its proposed coreceptor, BAK1, suggesting that BKI1 prevents the activation of BRI1.

Amino Acid Sequence↗
PubMed2000

Perception of brassinosteroids by the extracellular domain of the receptor kinase BRI1.

An assay was developed to study plant receptor kinase activation and signaling mechanisms. The extracellular leucine-rich repeat (LRR) and transmembrane domains of the Arabidopsis receptor kinase BRI1, which is implicated in brassinosteroid signaling, were fused to the serine/threonine kinase domain of XA21, the rice disease resistance receptor. The chimeric receptor initiates plant defense responses in rice cells upon treatment with brassinosteroids. These results, which indicate that the extracellular domain of BRI1 perceives brassinosteroids, suggest a general signaling mechanism for the LRR receptor kinases of plants. This system should allow the discovery of ligands for the LRR kinases, the largest group of plant receptor kinases.

Arabidopsis↗
PubMed2006

A proteomics study of the mung bean epicotyl regulated by brassinosteroids under conditions of chilling stress.

Mung bean CYP90A2 is a putative brassinosteroid (BR) synthetic gene that shares 77% identity with the Arabidopsis CPD gene. It was strongly suppressed by chilling stress. This implies that exogenous treatment with BR could allow the plant to recover from the inhibited growth caused by chilling. In this study, we used proteomics to investigate whether the mung bean epicotyl can be regulated by brassinosteroids under conditions of chilling stress. Mung bean epicotyls whose growth was initially suppressed by chilling partly recovered their ability to elongate after treatment with 24-epibrassinolde; 17 proteins down-regulated by this chilling were re-up-regulated. These up-regulated proteins are involved in methionine assimilation, ATP synthesis, cell wall construction and the stress response. This is consistent with the re-up-regulation of methionine synthase and S-adenosyl-L-methionine synthetase, since chilling-inhibited mung bean epicotyl elongation could be partially recovered by exogenous treatment with DL-methionine. This is the first proteome established for the mung bean species. The regulatory relationship between brassinosteroids and chilling conditions was investigated, and possible mechanisms are discussed herein.

Adaptation, Physiological↗
PubMed2002

Brassinosteroid mutants uncover fine tuning of phytochrome signaling.

Phytochromes (phy) A and B provide higher plants the ability to perceive divergent light signals. phyB mediates red/far-red light reversible, low fluence responses (LFR). phyA mediates both very-low-fluence responses (VLFR), which saturate with single or infrequent light pulses of very low fluence, and high irradiance responses (HIR), which require sustained activation with far-red light. We investigated whether VLFR, LFR, and HIR are genetically coregulated. The Arabidopsis enhanced very-low-fluence response1 mutant, obtained in a novel screening under hourly far-red light pulses, showed enhanced VLFR of hypocotyl growth inhibition, cotyledon unfolding, blocking of greening, and anthocyanin synthesis. However, eve1 showed reduced LFR and HIR. eve1 was found allelic to the brassinosteroid biosynthesis mutant dim/dwarf1. The analysis of both the brassinosteroid mutant det2 in the Columbia background (where VLFR are repressed) and the phyA eve1 double mutant indicates that the negative effect of brassinosteroid mutations on LFR requires phyA signaling in the VLFR mode but not the expression of the VLFR. Under sunlight, hypocotyl growth of eve1 showed little difference with the wild type but failed to respond to canopy shadelight. We propose that the opposite regulation of VLFR versus LFR and HIR could be part of a context-dependent mechanism of adjustment of sensitivity to light signals.

Anthocyanins↗
PubMed1982

Synthesis of brassinosteroids and relationship of structure to plant growth-promoting effects.

A number of brassinosteroids with and without hydroxyl groups or an alkyl substituent in their side chain were synthesized. The alkyl substituent at C-24 highly influenced the oxidation of the C-22 double bond with osmium tetroxide and, hence the ratio of the 22 beta,23 beta- and 22 alpha,23 alpha-glycolic isomers obtained. Two different bean bioassays used to compare the plant growth-promoting capabilities of these compounds and of brassinolide and its three side chain 22,23-cis-glycolic isomers showed that brassinolide was the most active. The next most active brassinosteroids were generally those with 22 alpha-OH, 23 alpha-OH orientation and a beta-methyl or alpha-ethyl substituent at C-24. Similarly, of the synthetic precursor tetrahydroxy ketones of the brassinosteroids, those with 22 alpha-OH, 23 alpha-OH orientation (like brassinolide) and an alkyl group at C-24 were also the most active in both bioassays. The results indicate stringent structural features are required for a steroid to induce brassin activity. The structural requirements are: a trans A/B ring system (5alpha-hydrogen), a 6-ketone or a 7-oxa-6-ketone system in ring B, cis alpha-oriented hydroxyl groups at C-2 and C-3, cis hydroxy groups at C-22 and C-23 as well as a methyl or ethyl substituent at C-24.

Biological Assay↗
PubMed2005

Brassinosteroids are inherently biosynthesized in the primary roots of maize, Zea mays L.

GC-MS analysis revealed that primary roots of maize contain 6-deoxocathasterone, 6-deoxoteasterone and 6-deoxotyphasterol. These brassinosteroids, and the previously identified campesterol, campestanol, 6-deoxocastasterone and castasterone, in the roots are members of a biosynthetic pathway to castasterone, namely the late C-6 oxidation pathway, suggesting that its biosynthetic pathway is operative in the roots. To verify this, a cell-free enzyme extract was prepared from maize roots, and enzymatic conversions from campesterol to castasterone through the aforementioned sterols and brassinosteroids were examined. The presence for the biosynthetic sequences, campesterol-->24-methylcholest-4-en-3beta-ol-->24-methylcholest-4-en-3-one-->24-methylcholest-5 alpha-cholestan-3-one-->campestanol and 6-deoxoteasterone-->6-deoxo-3-dehydroteasterone-->6-deoxotyphasterol-->6-deoxocastasterone-->castasterone were demonstrated. These results indicate that maize roots contain a complete set of enzymes involved in the late C-6 oxidation pathway, thereby demonstrating that endogenous brassinosteroids are biosynthesized in the roots.

Models, Chemical↗
PubMedDate not supplied

In vitro and in vivo antiherpetic activity of three new synthetic brassinosteroid analogues.

Brassinosteroids are a novel group of steroids that appear to be ubiquitous in plants and are essential for normal plant growth and development. It has been previously reported that brassinosteroid analogues exert an antiviral activity against herpes simplex virus type 1 (HSV-1) and arenaviruses. In the present study, we report the chemical synthesis of compounds (22S,23S)-3beta-bromo-5alpha,22,23-trihydroxystigmastan-6-one (2), (22S,23S)-5alpha-fluoro-3beta-22,23-trihydroxystigmastan-6-one (3), (22S,23S)-3beta,5alpha,22,23-tetrahydroxy-stigmastan-6-one (4) as well as their antiherpetic activity both in a human conjunctive cell line (IOBA-NHC) and in the murine herpetic stromal keratitis (HSK) experimental model. All compounds prevented HSV-1 multiplication in NHC cells in a dose dependent manner when added after infection with no cytotoxicity. Administration of compounds 2, 3, and 4 to the eyes of mice at 1, 2, and 3 days post-infection delayed and reduced the incidence of HSK, consisting mainly of inflammation, vascularization, and necrosis, compared to untreated, infected mice. However, viral titers of eye washes showed no differences among samples from treated and untreated mice. Since the decrease in the percentage of mice with ocular lesions occurred 5 days after treatment had ended, we suggest that brassinosteroids 2, 3, and 4 did not exert a direct antiviral effect in vivo, but rather may play a role in immune-mediated stromal inflammation, which would explain the improvement of the clinical signs of HSK observed.

Animals↗
PubMed2002

Brassinosteroid signal transduction: clarifying the pathway from ligand perception to gene expression.

Recent genetic screens for novel components of brassinosteroid signaling have revealed proteins with cell surface, cytoplasmic, and nuclear localization that function as either positive activators or negative regulators of the brassinosteroid response. Initial microarray experiments have expanded the number of known brassinosteroid-regulated genes, providing a useful resource for better understanding terminal events in signal transduction.

Arabidopsis↗
PubMed2005

Ca2+/calmodulin is critical for brassinosteroid biosynthesis and plant growth.

Brassinosteroids are plant-specific steroid hormones that have an important role in coupling environmental factors, especially light, with plant growth and development. How the endogenous brassinosteroids change in response to environmental stimuli is largely unknown. Ca2+/calmodulin has an essential role in sensing and transducing environmental stimuli. Arabidopsis DWARF1 (DWF1) is responsible for an early step in brassinosteroid biosynthesis that converts 24-methylenecholesterol to campesterol. Here we show that DWF1 is a Ca2+/calmodulin-binding protein and this binding is critical for its function. Molecular genetic analysis using site-directed and deletion mutants revealed that loss of calmodulin binding completely abolished the function of DWF1 in planta, whereas partial loss of calmodulin binding resulted in a partial dwarf phenotype in complementation studies. These results provide direct proof that Ca2+/calmodulin-mediated signalling has a critical role in controlling the function of DWF1. Furthermore, we observed that DWF1 orthologues from other plants have a similar Ca2+/calmodulin-binding domain, implying that Ca2+/calmodulin regulation of DWF1 and its homologues is common in plants. These results raise the possibility of producing size-engineered crops by altering the Ca2+/calmodulin-binding property of their DWF1 orthologues.

Amino Acid Sequence↗
PubMed2006

Heterotrimeric G protein alpha subunit is involved in rice brassinosteroid response.

Heterotrimeric G proteins are known to function as messengers in numerous signal transduction pathways. The null mutation of RGA (rice heterotrimeric G protein alpha subunit), which encodes the alpha subunit of heterotrimeric G protein in rice, causes severe dwarfism and reduced responsiveness to gibberellic acid in rice. However, less is known about heterotrimeric G protein in brassinosteroid (BR) signaling, one of the well-understood phytohormone pathways. In the present study, we used root elongation inhibition assay, lamina inclination assay and coleoptile elongation analysis to demonstrated reduced sensitivity of d1 mutant plants (caused by the null mutation of RGA) to 24-epibrassinolide (24-epiBL), which belongs to brassinosteroids and plays a wide variety of roles in plant growth and development. Moreover, RGA transcript level was decreased in 24-epiBL-treated seedlings in a dose-dependent manner. Our results show that RGA is involved in rice brassinosteroid response, which may be beneficial to elucidate the molecular mechanisms of G protein signaling and provide a novel perspective to understand BR signaling in higher plants.

Arabidopsis Proteins↗
PubMed1999

Inactivation of brassinosteroid biological activity by a salicylate-inducible steroid sulfotransferase from Brassica napus.

Recent discoveries from brassinosteroid-deficient mutants led to the recognition that plants, like animals, use steroids to regulate their growth and development. We describe the characterization of one member of a Brassica napus sulfotransferase gene family coding for an enzyme that catalyzes the O-sulfonation of brassinosteroids and of mammalian estrogenic steroids. The enzyme is specific for the hydroxyl group at position 22 of brassinosteroids with a preference for 24-epicathasterone, an intermediate in the biosynthesis of 24-epibrassinolide. Enzymatic sulfonation of 24-epibrassinolide abolishes its biological activity in the bean second internode bioassay. This mechanism of hormone inactivation by sulfonation is similar to the modulation of estrogen biological activity observed in mammals. Furthermore, the expression of the B. napus steroid sulfotransferase genes was found to be induced by salicylic acid, a signal molecule in the plant defense response. This pattern of expression suggests that, in addition to an increased synthesis of proteins having antimicrobial properties, plants respond to pathogen infection by modulating steroid-dependent growth and developmental processes.

Amino Acid Sequence↗
PubMed2005

A brassinosteroid-hypersensitive mutant of BAK1 indicates that a convergence of photomorphogenic and hormonal signaling modulates phototropism.

The phototropic response of Arabidopsis (Arabidopsis thaliana) is induced by the phototropin photoreceptors and modulated by the cryptochrome and phytochrome photoreceptors. Downstream of these photoreceptors, asymmetric lateral redistribution of auxin underlies the differential growth, which results in phototropism. Historical physiological evidence and recent analysis of hormone-induced gene expression demonstrate that auxin and brassinosteroid signaling function interdependently. Similarly, in this study we report evidence that interactions between brassinosteroids and auxin signaling modulate phototropic responsiveness. We found that elongated, a previously identified photomorphogenesis mutant, enhances high-light phototropism and represents a unique allele of BAK1/SERK3, a receptor kinase implicated in brassinosteroid perception. Altogether, our results support the hypothesis that phototropic responsiveness is modulated by inputs that influence control of auxin response factor-mediated transcription.

Alleles↗
PubMed1983

Investigations on the Mechanism of the Brassinosteroid Response: I. Indole-3-acetic Acid Metabolism and Transport.

A brassinosteroid treatment of light-grown first internode sections of Phaseolus vulgaris results in an increased bending response following unilateral indole-3-acetic acid (IAA) application. Reverse isotope dilution analysis shows that this increased response is not due to an increase in the concentration of applied IAA in the tissue or a change in the amount of IAA conjugated. Treatment with the brassinosteroid also does not affect the rate of IAA transport as measured using the agar block method. These results indicate that even though brassinosteroid potentiates auxin action, it does not have a direct effect on IAA uptake, metabolism, or cell to cell transport.

Journal Article↗
PubMed1987

Investigations on the Mechanism of the Brassinosteroid Response: VI. Effect of Brassinolide on Gravitropism of Bean Hypocotyls.

Brassinosteroids are steroidal lactones of plant origin that promote growth of a number of plant systems, and particularly the growth induced by auxins. Biologically active brassinosteroids (BR) also promote the growth of gravisensitive hypocotyls of 7-day-old light grown Phaseolus vulgaris when gravistimulated. Brassinolide-mediated promotion of curvature of gravistimulated internodes occurs in the absence of exogenously supplied indole-3-acetic acid (IAA). This is in contrast to the BR-promoted bending of vertically positioned bean hypocotyls, which is dependent upon exogenous IAA. Brassinosteroid treatment increased the graviperception of young internode tissues and the bending of the gravistimulated sections as well as the subsequent reversal of bending after the sections were placed vertically. These results indicate that BR sensitizes bean hypocotyls to gravistimulation and potentiates the action of a growth factor that induces gravitropic growth.

Journal Article↗
PubMed2001

Biological evaluation of 5-substituted pyrimidine derivatives as inhibitors of brassinosteroid biosynthesis.

A series of 5-substituted pyrimidine derivatives was synthesized, and their ability to inhibit brassinosteroid biosynthesis was tested. The biological activity of these compounds was evaluated by the cress stem elongation method. Among the synthesized compounds, alpha-(4-chlorophenyl)-alpha-phenyl-5-pyrimidinemethanol (DPPM 4) exhibited potent inhibitory activity for retarding cress stem elongation in the light. This inhibition was reversed by the application of 10 nM brassinolide, but not by 1 microM GA3. DPPM 4 also affected Arabidopsis growth in the dark. DPPM 4-treated Arabidopsis had phenotypes like those of brassinosteroid-deficient mutants, with short hypocotyls and open cotyledons, in the dark. These biological changes were restored by the co-application of 10 nM brassinolide, but not by 1 microM GA3, suggesting that the primary site of action of DPPM 4 was the brassinosteroid biosynthetic pathway.

Phenotype↗
PubMedDate not supplied

Action of brassinosteroids on the epithelial cell line from Chironomus tentans.

The two brassinosteroids, 22 S,23 S-homobrassinolide and 22 S,23 S-homocastasterone are weak competitors of the binding of [3H]ponasterone A to the intracellular ecdysteroid receptor from the epithelial cell line from Chironomus tentans. The relative affinities to the ecdysteroid receptor are 0.001 for both brassinosteroids as compared to 20-OH-ecdysone and 0.1 in comparison to ecdysone. Both substances exert morphological effects similar to those observed with 20-OH-ecdysone. Like moulting hormones both brassinosteroids inhibit chitin synthesis. However, these effects were observed only at rather high concentrations (10(-5) to 10(-4) M) which were cytotoxic for 22 S,23 S-homobrassinolide.

Acetylcholinesterase↗
PubMed2004

Arabidopsis constitutive photomorphogenic mutant, bls1, displays altered brassinosteroid response and sugar sensitivity.

We have isolated an Arabidopsis mutant impaired in light- and brassinosteroid (BR) induced responses, as well as in sugar signalling. The bls1 (brassinosteroid, light and sugar1) mutant displays short hypocotyl, expanded cotyledons, and de-repression of light-regulated genes in young seedlings, and leaf differentiation and silique formation on prolonged growth in dark. In light, the bls1 mutant is dwarf and develops a short root, compact rosette, with reduced trichome number, and exhibits delayed bolting. The activity of the BR inducible TCH4 and auxin inducible SAUR promoters, fused with GUS gene, is also altered in seedlings harbouring bls1 mutant background. In addition, the bls1 mutant is hypersensitive to metabolizable sugars. The short hypocotyl phenotype in dark, short root phenotype in light and sugar hypersensitivity could be rescued with BR application. Moreover, the bls1 mutant also showed higher expression of a BR biosynthetic pathway gene CPD, which is known to be feedback-regulated by BR. Using a genome-wide AFLP mapping strategy, the bls1 mutant has been mapped to a 1.4 Mb region of chromosome 5. Since no other mutant with essentially a similar phenotype has been assigned to this region, we suggest that the bls1 mutant defines a novel locus involved in regulating endogenous BR levels, with possible ramifications in integrating light, hormone and sugar signalling.

Abscisic Acid↗