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PubMed2001

Brassinolide may control aquaporin activities in Arabidopsis thaliana.

It is usually assumed that aquaporins present in the cellular membranes could be an important route in the control of water flux in plants, but evidence for this hypothesis is scarce. In this paper, we report measurements of the osmotic permeability (P(os) of protoplasts isolated from hypocotyls of wild-type and mutant Arabidopsis thaliana (L.) Heynh. Mutants were affected in their growth and exhibited different sensitivities to the phytohormone, brassinolide. For the two mutants studied (cpd: constitutive photomorphogenesis and dwarfism; bril: brassinosteroid insensitive), hypocotyl length was correlated to P(os) for the protoplasts. Under experimental conditions where hypocotyl growth had ceased, restoration of root, hypocotyl and petiole growth by brassinolide was correlated with an increase in P(os) of the hypocotyl protoplasts. We consider that the increase in Pos of the hypocotyl cells was needed because these cells were part of the transcellular water pathway of the plant. This is the first time, to our knowledge, that brassinolide has been shown to be involved in the modification of the water-transport properties of cell membranes. Our results also emphasize the importance of aquaporins and the transcellular pathway in water transport under normal growth conditions.

Aquaporins↗
PubMed2005

Functional analysis of the BIN 2 genes of cotton.

Brassinosteroids (BR) promote the elongation of cotton fibers and may be a factor in determining their final length. To begin to understand the role of BR-mediated responses in the development of cotton fibers we have characterized the BIN 2 genes of cotton. BIN 2 is a member of the shaggy-like protein kinase family that has been identified as a negative regulator of BR signaling in Arabidopsis. Sequence analyses indicate that the tetraploid cotton genome includes four genes with strong sequence similarity to BIN 2. These genes fall into two distinct subclasses based on sequence and expression patterns. Sequence comparisons with corresponding genes from cotton species that have the diploid A and D genomes, respectively, shows that each pair of genes comprises homeologs derived from the A and D sub-genomes. Transgenic Arabidopsis plants that express these cotton BIN 2 cDNAs show reduced growth and similar phenotypes to the semi-dominant bin 2 mutant plants. These results indicate that the cotton BIN 2 genes encode functional BIN 2 isoforms that can inhibit BR signaling. Further analyses of the function of BIN 2 genes and their possible roles in determining fiber yield and quality are underway.

Amino Acid Sequence↗
PubMed1995

Brassinolide is a selective ribosomal cistron regulator in onion leaf base tissue.

Outer epidermal cells from the basal, equatorial, near-apical, and apical regions of the third turgid onion (Allium cepa L. var. yellow, sweet Spanish) leaf base were treated (3 and 6 h in the dark = T3 and T6, respectively) with brassinolide (Br, a brassinosteroid plant growth regulator; effects on excised pieces compared with those in water controls: there were no statistical differences between the T3 and T6 results). Br induced increases in the volume and changes in morphologies of the major nucleoli to a greater extent than observed for major nucleoli in basal through near-apical controls. No major nucleoli were activated in control or Br-treated apical tissue. Minor nucleolar organizer regions in control and Br-treated tissue remained inactive in all locations. We propose that Br is a major ribosomal cistron regulator.

Allium↗
PubMed2005

Shoot-applied polyamines suppress nodule formation in soybean (Glycine max).

In legumes, the number of root nodules is controlled by a mechanism called autoregulation. Recently, we found that the foliar brassinosteroid (BR), a plant growth-regulating hormone, systemically regulates the nodule number in soybean plants. In the present study we report that such down-regulation of root nodule formation by a BR may occur through a change of the polyamine contents, with the experimental evidence as follows. The foliar contents of both spermidine (Spd) and spermine (Spm) in the super-nodulating soybean mutant, En6500, were always lower than those in its parent line, Enrei. This lower Spd and Spm content accompanied a striking accumulation of putrescine (Put) in the former plant. This finding indicates that Spd and Spm biosynthesis from their precursor Put is repressed in En6500. The foliar treatments with Spd or Spm of En6500 led to a reduction of both nodule number and root growth. On the other hand, foliar treatment with MDL74038, a specific inhibitor of Spd biosynthesis, apparently increased the root nodule number in Enrei. Foliar application of brassinolide (BL) of En6500 increased the leaf Spd level and reduced the nodule number. These results suggested that BL-induced Spd synthesis in shoots might suppress the root nodule formation.

Brassinosteroids↗
PubMed2006

OsBLE3, a brassinolide-enhanced gene, is involved in the growth of rice.

Brassinosteroids (BRs) are a group of plant hormones involved in a wide range of plant growth and developmental processes. To investigate the mechanism of BR action in monocots, a brassinolide (BL) upregulated gene designated OsBLE3 was identified, cloned and characterized in rice. It was mainly expressed in roots and leaf sheaths with levels of expression directly dependent on the dose of BL. In situ hybridization detected OsBLE3 mRNA in the shoot apical meristem, organ primordia and vascular tissue. Furthermore, its expression was enhanced by co-treatment with BL and low concentrations of IAA. These results, and the existence of auxin response elements in the 5'-flanking region of the OsBLE3 gene, indicate that OsBLE3 expression is under control of both BR and auxin. The GUS reporter gene driven by a 2277 bp OsBLE3 putative promoter was mainly expressed in vascular tissues, branch root primordia and was responsive to exogenous BL treatment. OsBLE3 transcript levels were greatly reduced in brd1 plants, a BL deficient mutant, compared to the wild type control. In OsBRI1 antisense transgenic rice and OsBLE3, the BR-insensitive mutant expression of OsBLE3 in response to exogenous BL treatment was significantly lower compared to that in control plants transformed with a vacant vector. Reduced OsBLE3 expression and growth retardation was also observed in OsBLE3 antisense transgenic rice plants. Internode cell length of the OsBLE3 antisense transgenic lines was about 70% of that in the vacant vector transformed control lines. These results suggest that OsBLE3 is involved in cell elongation in rice through dual regulation by BL and IAA.

Amino Acid Sequence↗
PubMed2004

Molecular cloning and characterization of a novel brassinolide enhanced gene OsBLE1 in Oryza sativa seedlings.

Brassinosteroids (BRs) are plant steroids essential for normal growth and development. To gain insight into the molecular mechanism by which BRs regulate the growth and development of plants, it is necessary to identify and analyze more genes that are regulated by BRs. A novel brassinolide (BL)-enhanced gene designated OsBLE1, which was originally identified by using rice (Oryza sativa L.) cDNA microarray, was cloned and characterized. Its cDNA is 598 bp long, encoding a predicted polypeptide with 81 amino acid residues. Northern blots analysis revealed that OsBLE1 expression began to increase at 6 h and reached its maximum at 12 h after BL treatment. OsBLE1 expression was most responsive to BL in lamina joint in rice seedlings; besides, IAA and GA3 also enhanced its expression. OsBLE1 expressed mainly in active tissues such as vascular bundles and root primordial. Transgenic rice expressing antisense OsBLE1 exhibits various degrees of repressed growth. Results suggest that OsBLE1 might be involved in BL-regulated growth processes in rice seedlings.

Amino Acid Sequence↗
PubMed2003

Crystal structure of a hypoallergenic isoform of the major birch pollen allergen Bet v 1 and its likely biological function as a plant steroid carrier.

Bet v 1l is a naturally occurring hypoallergenic isoform of the major birch pollen allergen Bet v 1. The Bet v 1 protein belongs to the ubiquitous family of pathogenesis-related plant proteins (PR-10), which are produced in defense-response to various pathogens. Although the allergenic properties of PR-10 proteins have been extensively studied, their biological function in plants is not known. The crystal structure of Bet v 1l in complex with deoxycholate has been determined to a resolution of 1.9A using the method of molecular replacement. The structure reveals a large hydrophobic Y-shaped cavity that spans the protein and is partly occupied by two deoxycholate molecules which are bound in tandem and only partially exposed to solvent. This finding indicates that the hydrophobic cavity may have a role in facilitating the transfer of apolar ligands. The structural similarity of deoxycholate and brassinosteroids (BRs) ubiquitous plant steroid hormones, prompted the mass spectrometry (MS) study in order to examine whether BRs can bind to Bet v 1l. The MS analysis of a mixture of Bet v 1l and BRs revealed a specific non-covalent interaction of Bet v 1l with brassinolide and 24-epicastasterone. Together, our findings are consistent with a general plant-steroid carrier function for Bet v 1 and related PR-10 proteins. The role of BRs transport in PR-10 proteins may be of crucial importance in the plant defense response to pathological situations as well as in growth and development.

Allergens↗
PubMed2002

Glycogen synthase kinase 3/SHAGGY-like kinases in plants: an emerging family with novel functions.

Animal glycogen synthase kinase 3 (GSK-3)/SHAGGY kinases have been studied for more than 20 years, whereas plant glycogen synthase kinase 3/SHAGGY-like kinases (GSKs) have only recently entered the scene. Present evidence indicates that plant GSKs are involved in different processes, such as flower development, brassinosteroid signaling, NaCl stress and wound responses. In contrast to mammals, which contain two genes, plants have a multigene family of GSKs. Analysis of the Arabidopsis genome revealed the existence of ten GSK genes that fall into four distinct subfamilies. We discuss the functions and mechanisms of GSK action in plants and other organisms.

Animals↗
PubMed2003

Genome organization in Arabidopsis thaliana: a survey for genes involved in isoprenoid and chlorophyll metabolism.

The isoprenoid biosynthetic pathway provides intermediates for the synthesis of a multitude of natural products which serve numerous biochemical functions in plants: sterols (isoprenoids with a C30 backbone) are essential components of membranes; carotenoids (C40) and chlorophylls (which contain a C20 isoprenoid side-chain) act as photosynthetic pigments; plastoquinone, phylloquinone and ubiquinone (all of which contain long isoprenoid side-chains) participate in electron transport chains; gibberellins (C20), brassinosteroids (C30) and abscisic acid (C15) are phytohormones derived from isoprenoid intermediates; prenylation of proteins (with C15 or C20 isoprenoid moieties) may mediate subcellular targeting and regulation of activity; and several monoterpenes (C10), sesquiterpenes (C15) and diterpenes (C20) have been demonstrated to be involved in plant defense. Here we present a comprehensive analysis of genes coding for enzymes involved in the metabolism of isoprenoid-derived compounds in Arabidopsis thaliana. By combining homology and sequence motif searches with knowledge regarding the phylogenetic distribution of pathways of isoprenoid metabolism across species, candidate genes for these pathways in A. thaliana were obtained. A detailed analysis of the vicinity of chromosome loci for genes of isoprenoid metabolism in A. thaliana provided evidence for the clustering of genes involved in common pathways. Multiple sequence alignments were used to estimate the number of genes in gene families and sequence relationship trees were utilized to classify their individual members. The integration of all these datasets allows the generation of a knowledge-based metabolic map of isoprenoid metabolic pathways in A. thaliana and provides a substantial improvement of the currently available gene annotation.

Abscisic Acid↗
PubMed2003

A novel brassinolide-enhanced gene identified by cDNA microarray is involved in the growth of rice.

Brassinosteroids (BRs) are growth-promoting natural substances required for normal plant growth and development. To understand the molecular mechanism of BR action, a cDNA microarray containing 1265 rice genes was analyzed for expression differences in rice lamina joint treated with brassinolide (BL). A novel BL-enhanced gene, designated OsBLE2, was identified and cloned. The full-length cDNA is 3243 bp long, encoding a predicted polypeptide of 761 amino acid residues and nine possible transmembrane regions. OsBLE2 expression was most responsive to BL in the lamina joint and leaf sheath in rice seedlings. Besides, auxin and gibberellins also increased its expression. OsBLE2 expressed more, as revealed by in situ hybridization, in vascular bundles and root primordia, where the cells are actively undergoing division, elongation, and differentiation. Transgenic rice expressing antisense OsBLE2 exhibits various degrees of repressed growth. BL could not enhance its expression in transgenic rice expressing antisense BRI1, a BR receptor, indicating that BR signaling to the enhanced expression of OsBLE2 is through BRI1 . BL effect in the d1 mutant rice was much weaker than that in its wild-type control, indicating that heterotrimeric G protein may be a component of BRs signaling. These results suggest that OsBLE2 is involved in BL-regulated growth and development processes in rice.

Amino Acid Sequence↗
PubMed2003

Activation of cell proliferation by brassinolide application in tobacco BY-2 cells: effects of brassinolide on cell multiplication, cell-cycle-related gene expression, and organellar DNA contents.

Brassinosteroids (BRs) are steroidal phytohormones that are essential for many processes in plant growth and development, such as cell expansion, vascular differentiation, and responses to stress. The effects of BRs on cell division are unclear, as attested by contradictory published results. To determine the effect of BRs on cell division, the tobacco (Nicotiana tabacum) BY-2 cell line, which is a widely-used model system in plant cell biology, was used. It was found that brassinolide (BL) promoted cell division only during the early phase of culture and in the absence of auxin (2,4-D). This promotion of cell division was confirmed by RNA gel blot analyses using cell-cycle-related gene probes. At later stages in the culturing periods of BL-supplied and 2,4-D-supplied BY-2 cells, differences in cell multiplication and cell-cycle-related gene expression were observed. Moreover, the BL-treated BY-2 cells had morphological differences from the 2,4-D-treated cells. To determine whether suppressed organellar DNA replication limited this promotion of cell division during the early culture phase, this replication was examined and it was found that BL treatment had no effect on activating organellar (plastid- and mitochondrial-) DNA synthesis. As preferential organellar DNA synthesis, which is activated by 2,4-D, is necessary during successive cell divisions in BY-2 cells, these data suggest that the mechanism of the promotion of cell division by BL treatment is distinct from that regulated by the balance of auxin and cytokinin.

Brassinosteroids↗
PubMed2006

An early auxin-responsive Aux/IAA gene from wheat (Triticum aestivum) is induced by epibrassinolide and differentially regulated by light and calcium.

The plant hormone auxin plays a central role in regulating many aspects of plant growth and development. This largely occurs as a consequence of changes in gene expression. The Aux/IAA genes are best characterized among the early auxin-responsive genes, which encode short-lived transcriptional repressors. In most plants examined, including Arabidopsis, soybean, and rice, the Aux/IAA genes constitute a large gene family. By screening the available databases, at least 15 expressed sequence tags (ESTs) have been identified from wheat (Triticum aestivum), which exhibit high sequence identity with Aux/IAA homologues in other species. One of these Aux/IAA genes, TaIAA1, harbouring all the four conserved domains characteristic of the Aux/IAA proteins, has been characterized in detail. The expression of TaIAA1 is light-sensitive, tissue-specific, and is induced within 15-30 min of exogenous auxin application. Also, the TaIAA1 transcript levels increase in the presence of a divalent cation, Ca(2+), and this effect is reversed by the calcium-chelating agent, EGTA. The TaIAA1 gene qualifies as the primary response gene because an increase in its transcript levels by auxin is unaffected by cycloheximide. In addition to auxin, the TaIAA1 gene is also induced by brassinosteroid, providing evidence that interplay between hormones is crucial for the regulation of plant growth and development.

Blotting, Southern↗
PubMed2000

Brassinolide and [26, 28-2H6]brassinolide are differently demethylated by loss of C-26 and C-28, respectively, in Marchantia polymorpha.

Metabolism of brassinolide in Marchantia polymorpha was investigated by use of in vivo suspension cultured cells. GC-MS analysis of metabolites derived from non-labelled brassinolide and [26, 28-2H6] brassinolide revealed that brassinolide was converted to 26-norbrassinolide while [26, 28-2H6]brassinolide to [26-2H3]28-norbrassinolide. It seems that Marchantia cells recognized [26, 28-2H6]brassinolide as a xenobiotic rather than brassinolide and deteriums attached to C-28 significantly affect demethylation reaction due to isotopic effect. Thus, demethylation of brassinolide in planta seems to proceed by loss of C-26 rather than C-28. The present finding is the first evidence for demethylation metabolism of brassinosteroids. The biological activity of 26-norbrassinolide was 10-fold reduced as shown by the rice lamina inclination test. However, because of its high biological activity, it remains difficult to conclude whether or not C-26 demethylation serves as an important deactivation process of brassinolide.

Brassinosteroids↗
PubMed2002

Role of a heterotrimeric G protein in regulation of Arabidopsis seed germination.

Seed germination is regulated by many signals. We investigated the possible involvement of a heterotrimeric G protein complex in this signal regulation. Seeds that carry a protein null mutation in the gene encoding the alpha subunit of the G protein in Arabidopsis (GPA1) are 100-fold less responsive to gibberellic acid (GA), have increased sensitivity to high levels of Glc, and have a near-wild-type germination response to abscisic acid and ethylene, indicating that GPA1 does not directly couple these signals in germination control. Seeds ectopically expressing GPA1 are at least a million-fold more responsive to GA, yet still require GA for germination. We conclude that the GPA1 indirectly operates on the GA pathway to control germination by potentiation. We propose that this potentiation is directly mediated by brassinosteroids (BR) because the BR response and synthesis mutants, bri1-5 and det2-1, respectively, share the same GA sensitivity as gpa1 seeds. Furthermore, gpa1 seeds are completely insensitive to brassinolide rescue of germination when the level of GA in seeds is reduced. A lack of BR responsiveness is also apparent in gpa1 roots and hypocotyls suggesting that BR signal transduction is likely coupled by a heterotrimeric G protein at various points in plant development.

Abscisic Acid↗
PubMed2003

Sterols regulate development and gene expression in Arabidopsis.

Sterols are important not only for structural components of eukaryotic cell membranes but also for biosynthetic precursors of steroid hormones. In plants, the diverse functions of sterol-derived brassinosteroids (BRs) in growth and development have been investigated rigorously, yet little is known about the regulatory roles of other phytosterols. Recent analysis of Arabidopsis fackel (fk) mutants and cloning of the FK gene that encodes a sterol C-14 reductase have indicated that sterols play a crucial role in plant cell division, embryogenesis, and development. Nevertheless, the molecular mechanism underlying the regulatory role of sterols in plant development has not been revealed. In this report, we demonstrate that both sterols and BR are active regulators of plant development and gene expression. Similar to BR, both typical (sitosterol and stigmasterol) and atypical (8, 14-diene sterols accumulated in fk mutants) sterols affect the expression of genes involved in cell expansion and cell division. The regulatory function of sterols in plant development is further supported by a phenocopy of the fk mutant using a sterol C-14 reductase inhibitor, fenpropimorph. Although fenpropimorph impairs cell expansion and affects gene expression in a dose-dependent manner, neither effect can be corrected by applying exogenous BR. These results provide strong evidence that sterols are essential for normal plant growth and development and that there is likely a BR-independent sterol response pathway in plants. On the basis of the expression of endogenous FK and a reporter gene FK::beta-glucuronidase, we have found that FK is up-regulated by several growth-promoting hormones including brassinolide and auxin, implicating a possible hormone crosstalk between sterol and other hormone-signaling pathways.

Arabidopsis↗
PubMed2004

Overexpression of constitutive differential growth 1 gene, which encodes a RLCKVII-subfamily protein kinase, causes abnormal differential and elongation growth after organ differentiation in Arabidopsis.

To better understand genetic regulation of differential growth of plant organs, a dominant and semidwarf mutant, constitutive differential growth 1-Dominant (cdg1-D), was isolated utilizing the technique of activation tagging. cdg1-D showed pleiotropic phenotype including dwarfism, exaggerated leaf epinasty, and twisted or spiral growth in hypocotyl, inflorescence stem, and petiole. Hypocotyls of cdg1-D were longer than those of wild type under light conditions. The phenotype was caused by activation tagging of CDG1 gene that encodes a receptor-like cytoplasmic kinase of RLCKVII subfamily. When treated with high concentrations of brassinolide, light-grown wild-type seedlings showed long hypocotyls and strong leaf epinasty as observed in cdg1-D seedlings. Treatment of cdg1-D with brassinazole, a specific inhibitor of brassinosteroid (BR) biosynthesis, did not rescue the mutant phenotype. Gene expression of CONSTITUTIVE PHOTOMORPHOGENESIS AND DWARFISM involved in BR biosynthesis and phyB ACTIVATION-TAGGED SUPPRESSOR1 that inactivates BR was repressed and induced, respectively, in cdg1-D plants, suggesting constitutive activation of BR signaling in the mutant. CDG1 was expressed at a very low level in all the organs of the wild type tested. We isolated two independent intragenic suppressors of cdg1-D. However, they showed normal morphology and responded to BR in a similar manner to wild type. Taken together, CDG1 gene may interfere with signal transduction of BR when overexpressed, but is not an essential factor for it in the wild type.

Amino Acid Sequence↗
PubMed2000

Biosynthetic pathways of brassinolide in Arabidopsis.

Our previous studies on the endogenous brassinosteroids (BRs) in Arabidopsis have provided suggestive evidence for the operation of the early C6-oxidation and the late C6-oxidation pathways, leading to brassinolide (BL) in Arabidopsis. However, to date the in vivo operation of these pathways has not been fully confirmed in this species. This paper describes metabolic studies using deuterium-labeled BRs in wild-type and BR-insensitive mutant (bri1) seedlings to establish the intermediates of the biosynthetic pathway of BL in Arabidopsis. The first evidence for the conversion of campestanol to 6-deoxocathasterone and the conversion of 6-deoxocathasterone to 6-deoxoteasterone is provided. The later biosynthetic steps (6-deoxoteasterone --> 3-dehydro-6-deoxoteasterone --> 6-deoxotyphasterol --> 6-deoxocastasterone --> 6alpha-hydroxycastasterone --> castasterone --> BL) were demonstrated by stepwise metabolic experiments. Therefore, these studies complete the documentation of the late C6-oxidation pathway. The biosynthetic sequence involved in the early C6-oxidation pathway (teasterone --> 3-dehydroteasterone --> typhasterol --> castasterone --> BL) was also demonstrated. These results show that both the early and late C6-oxidation pathways are functional in Arabidopsis. In addition we report two new observations: the presence of a new branch in the pathway, C6 oxidation of 6-deoxotyphasterol to typhasterol, and increased metabolic flow in BR-insensitive mutants.

Arabidopsis↗
PubMed1998

The Arabidopsis DIMINUTO/DWARF1 gene encodes a protein involved in steroid synthesis.

We have identified the function of the Arabidopsis DIMINUTO/DWARF1 (DIM/DWF1) gene by analyzing the dim mutant, a severe dwarf with greatly reduced fertility. Both the mutant phenotype and gene expression could be rescued by the addition of exogenous brassinolide. Analysis of endogenous sterols demonstrated that dim accumulates 24-methylenecholesterol but is deficient in campesterol, an early precursor of brassinolide. In addition, we show that dim is deficient in brassinosteroids as well. Feeding experiments using deuterium-labeled 24-methylenecholesterol and 24-methyldesmosterol confirmed that DIM/DWF1 is involved in both the isomerization and reduction of the Delta24(28) bond. This conversion is not required in cholesterol biosynthesis in animals but is a key step in the biosynthesis of plant sterols. Transient expression of a green fluorescent protein-DIM/DWF1 fusion protein and biochemical experiments showed that DIM/DWF1 is an integral membrane protein that most probably is associated with the endoplasmic reticulum.

Amino Acid Sequence↗