Cited by 270Plant Molecular Biology ResearchPlant biochemistry and biosynthesisLight effects on plants

Brassinosteroids and Plant Steroid Hormone Signaling

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Bishop, Gerard J., Koncz, Csaba·2002·The Plant Cell

Abstract

Structures of Steroid Hormones. Chemical structure of brassinolide and castasterone plant steroid hormones, in comparison with the mammalian sex steroid hormones testosterone and oestradiol, and the insect steroid hormone ecdysone. Highlighted are carbon numbers of BL having oxygen moieties that are important for BR activity. BR Biosynthesis Pathway. A simplified scheme of the BR biosynthesis pathway including steps of early and late C-6 oxidation that lead to the synthesis of BL (Noguchi et al., 2000; Shimada et al., 2001). Mutations in genes coding for key biosynthetic enzymes are in bold. det-2, DEETIOLATED-2, steroid 5α reductase (Li et al., 1996); dwf4, DWARF4 cytochrome P450 CYP90B, C-22 hydroxylase (Choe et al., 1998); cpd, CONSTITUTIVE PHOTOMORPHOGENIC and DWARFISM cytochrome P450 CYP90A, C-23 hydroxylase (Szekeres et al., 1996); dx, DWARF cytochrome P450 CYP85, C-6 oxidase (Bishop et al., 1996, 1999; Shimada et al., 2001); DDWF, DARK-INDUCED dwf-LIKE-1, cytochrome P450 CYP92A6, C-2 hydroxylase (Kang et al., 2001). In animal cells, steroid hormones are perceived by binding to their cognate nuclear steroid receptors, which are present in the cytoplasm. Once activated, the receptor complex is transferred to the nucleus to promote or repress transcription of hormone-responsive genes (Beato et al., 1995). This is called genomic signaling because it involves the genome in generating a physiological response. Steroid hormones can also elicit cellular responses in the presence of inhibitors of transcription or protein synthesis, and in enucleated cells. This mechanism is often referred to as nongenomic steroid signaling because it is not mediated by the genome. Some of the nongenomic signaling mechanisms imply a direct interaction between nuclear steroid receptors and other signaling molecules. Nongenomic steroid signaling pathways can also stimulate alterations in second messenger levels, ion fluxes, and protein kinase activities via as-yet uncharacterized steroid carrier proteins and plasma membrane–associated receptors (for reviews, see Wehling, 1997; Falkenstein et al., 2000). The annotation of the Arabidopsis genome sequence (Arabidopsis Genome Initiative, 2000) has confirmed the previous notion (Li and Chory, 1997; McCarty and Chory, 2000) that plants lack close homologs of animal nuclear steroid receptors. Steroid signaling in plants that also leads to alteration in transcription or a physiological response is therefore probably mediated by alternative mechanisms that may be similar to nongenomic steroid signaling in animals. This review highlights the characterization of genes and mutations that is beginning to reveal the mode of steroid hormone action in plants, but at the same time is mindful that this was preceded by the characterization of BR's effects on plant growth and development. To identify regulatory functions in plant steroid signaling, a genetic approach was exploited that aimed at the isolation of brassinosteroid insensitive (bri) Arabidopsis mutants (Clouse et al., 1996). Intriguingly, initial characterization of these bri mutants led only to the identification of multiple mutant alleles of the BRI1 gene, which was subsequently cloned by chromosome walking (Li and Chory, 1997). BRI1 encodes a leucine-rich repeat receptor-like kinase (LRR-RLK) that provides an important key to deciphering primary events in BR signaling. In addition to summarizing our current knowledge on the regulatory role of BRI1, this review provides a brief look at the characterization of further genes that is beginning to provide an insight into some intricate signaling functions controlling steroid hormone action in plants. The leaf bending caused by extracts from Distylium racemosum in the rice lamina inclination assay (Marumo et al., 1968) is one of the earliest reports of BR activity in plants. In this assay, BRs caused dose-dependent swelling of the adaxial cells in the joint between the leaf blade and sheath of etiolated rice seedlings. The angle of the leaf bending caused by the swelling is used as a sensitive bioassay during BR isolation and quantification procedures (Crozier et al. 2000). An early report on growth-promoting activity of “brassin,” from which BL was isolated, was based on BL-mediated stimulation of elongation of bean 2nd and 3rd internode, with higher concentrations causing splitting of the stem (Mitchell et al., 1970; Grove et al., 1979). BL and synthetic analogs were subsequently used in various bioassays, which indicated that in addition to leaf bending, cell elongation, and cell division, BL also effects source/sink relationships (Krizek and Mandava, 1983b), proton pumping and membrane polarization (Cerana et al., 1983; Romani et al., 1983), photosynthesis (Braun and Wild, 1984), and stress responses including thermotolerance (Wilen et al., 1995; Dhaubhadel et al., 1999) and senescence (Mandava et al., 1981). In addition to these effects, BRs promote vascular differentiation (Iwasaki a

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Crossref · 10.1105/tpc.001461

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Authors
Bishop, G. J., & Koncz, C.
Affiliations
Max Planck Society (DE)
Venue
The Plant Cell
Published
2002-05
Volume
14
Issue
suppl 1
Pages
S97-S110
ISSN
  • 1040-4651 (ISSN-L)
  • 1532-298X
OpenAlex
W1749881282
Cited by
270
References
109
Citations by year
2026: 5 · 2025: 10 · 2024: 8 · 2023: 11 · 2022: 9 · 2021: 12 · 2020: 13 · 2019: 10 · 2018: 9 · 2017: 10 · 2016: 9 · 2015: 9 · 2014: 17 · 2013: 6 · 2012: 15
FWCI
22.38
Type
journal article
Language
en
Open access
Locations
  • The Plant Cell (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • Max Planck Institute for Plasma Physics (submittedVersion)
  • Max Planck Digital Library (submittedVersion)
  • MPG.PuRe (Max Planck Society) (submittedVersion)
Topics
  • Life Sciences › Agricultural and Biological Sciences › Plant Science › Plant Molecular Biology Research
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Plant biochemistry and biosynthesis
  • Life Sciences › Agricultural and Biological Sciences › Plant Science › Light effects on plants
Keywords
brassinosteroids, brassinolide, castasterone, plant steroid hormones, steroidogenesis, cytochrome P450, non-genomic steroid action, nuclear steroid receptors, plant growth and development, plant hormones, ecdysone, testosterone, estradiol
MeSH terms
Cell Membrane, Cholestanols, Membrane Proteins, Mutation, Plant Growth Regulators, Protein Kinases, Steroids, Heterocyclic, Signal Transduction, Protein Serine-Threonine Kinases, Arabidopsis, Receptor Protein-Tyrosine Kinases, Arabidopsis Proteins, Brassinosteroids

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