SHY2 as a node in the regulation of root meristem development by auxin,brassinosteroids, and cytokinin

In multicellular organisms, the balance between cell division and differentiation determines organ size, and represents a central unknown in developmental biology. In Arabidopsis roots, this balance is mediated between cytokinin and auxin through a regulatory circuit converging on the IAA3/SHORT HYPOCOTYL 2 (SHY2) gene. Here, we show that crosstalk between brassinosteroids (BRs) and auxin occurs in the vascular transition zone to promote root meristem development. We found that BR increases root meristem size by up‐regulating expression of the PINFORMED 7 (PIN7) gene and down‐regulating expression of the SHY2 gene. In addition, BES1 could directly bind to the promoter regions of both PIN7 and SHY2, indicating that PIN7 and SHY2 mediate the BR‐induced growth of the root meristem by serving as direct targets of BES1. Moreover, the PIN7 overexpression and loss‐of‐function SHY2 mutant were sensitive to the effects of BR and could partially suppress the short‐root phenotypes associated with deficient BR signaling. Interestingly, BRs could inhibit the accumulation of SHY2 protein in response to cytokinin. Taken together, these findings suggest that a complex equilibrium model exists in which regulatory interactions among BRs, auxin, and cytokinin regulate optimal root growth.     

Brassinolide-2,3-acetonide: A brassinolide-induced rice lamina joint inclination antagonist

A novel chemical tool compound that is an antagonist of brassinolide (BL, 1)-induced rice lamina joint inclination was developed. Although 2-O-, 3-O-, 22-O-, or 23-O-methylation of BL causes a critical decrease in biological activity,⁵ a crystal structure of the extracellular leucine-rich repeat (LRR) domain of BRASSINOSTEROID-INSENSITIVE I (BRI1) bound to BL3, 4 indicates that the loss of activity of the O-methylated BL may result from not only the low affinity to BRI1, but also from blocking the interaction with another BR signaling factor, a partner protein of BRI1 (e.g., BRI1-ASSOCIATED KINASE 1, BAK1). On the basis of this hypothesis we synthesized the BL 2,3-acetonide 2, the 22,23-acetonide 3, and the 2,3:22,23-diacetonide 4 to assess the possibility of 2-O- and 3-O- or/and 22-O- and 23-O-alkylated BL as an antagonist in BR signaling evoked by exogenously applied BL. The 2,3-acetonide 2 more strongly inhibited the lamina inclination caused by BL relative to the 22,23-acetonide 3, whereas the diacetonide 4 had no effect most likely due to its increased hydrophobicity. This suggested that the 2,3-hydroxyl groups of BL play a more significant role in the interaction with a BRI1 partner protein rather than BRI1 itself in rice lamina joint inclination. Taken together it was demonstrated that BL, the most potent agonist of BRI1, is transformed into an antagonist by functionalization of the 2,3-dihydroxyl groups as the acetonide. This finding opens the door to the potential development of a chemical tool that modulates protein–protein interactions in the BR signaling pathway to dissect the BR-dependent processes.     

Synthesis of [26,27-2H6]brassinosteroids from 23,24-bisnorcholenic acid methyl ester

A number of hexadeuterated brassinosteroids (BS) containing a hydroxy group at C-22 or a 22R,23R-diol function were prepared starting from 23,24-bisnorcholenic acid methyl ester for biosynthetic studies. Synthesis of the cyclic part was accomplished via the initial hydroboration-oxidation of Delta(5)-double bond. The key step in the synthesis of the side chain involved addition of (2S)-[3,4-(2)H(6)]2,3-dimethylbutylphenyl sulfone to the corresponding C-22 aldehydes.     

Isolation and characterization of brassinosteroids from immature seeds of Camellia sinensis (O) Kuntze

Brassinosteroids play an important role in growth and development of plants. They have been reported universally in all the plants. The present study deals with the presence of these compounds in immature tea seeds. Five brassinosteroids, i.e. 6-deoxo-28-norcathasterone, 6-deoxo-28-norteasterone, 3-dehydro-6-deoxo-28-norteasterone, 6-deoxo-28-nortyphasterol and 6-deoxo-28-norcastasterone have been isolated and identified by GC–MS. The identified brassinosteroids and their derivatives are active constituents of late C-6 oxidation pathway, thereby suggesting the biosynthesis of brassinosteroids in tea seeds by late C-6 oxidation pathway.     

植物中油菜素类固醇信号转导与细胞增殖(综述)

BRI1/BAK1复合体感知油菜素类固醇(BR)后,通过基因表达变化和涉及V-ATPase的快速生长诱导反应的磷酸化级联放大作用传递信号,并影响细胞增殖增长过程。本文就植物中BR调节基因表达及其信号转导与细胞增殖作一综合介绍,并对存在的问题进行探讨。     

A rapid effect of applied brassinolide on abscisic acid concentrations in <Emphasis Type="Italic">Brassica napus</Emphasis> leaf tissue subjected to short-term heat stress

Three-week old canola (Brassica napus L.) seedlings grown at 20/16°C (day/night) were subjected to short-term (4 and 8 h) heat stress (45°C) or maintained at a normal temperature of 20°C. Half of the plants under each treatment received a 10⁻⁶ M solution of brassinolide (BL) 1 h prior to beginning the temperature treatments. The concentration (ng/g dry weight) of endogenous abscisic acid (ABA) was subsequently determined in young leaves via the stable isotope dilution method. Applied BL had no effect on endogenous ABA for plants maintained at normal temperatures. However, ABA concentration was significantly elevated by heat stress alone and doubled by heat stress + BL. These results suggest that the well-known enhancement of tolerance to high temperature stress that can be obtained by BL or 24-epi-BL applications may be caused by a brassinosteroid-induced elevation in endogenous ABA concentration.     

Isolation and Characterization of Brassinosteroids from Leaves of Camellia sinensis (L.) O. Kuntze

Brassinosteroids are of ubiquitous occurrence in plants and elicit a wide spectrum of physiological responses. In our study, brassinosteroids were isolated and identified in topmost dormant leaves of tea plants. Six brassinosteriods, i.e. 6-deoxocastasterone, 24-epibrassinolide,3-dehydroteasterone, typhasterol, 3-deoxotyphasterol and 28-homodolicholide, were isolated and identified by GC–MS. All the brassinosteroids identified belong to important components of early and late C6 oxidation pathways proposed for brassinosteroids biosynthesis in plants. It suggests that both pathways are operating in tea to produce brassinolide, the most active brassinosteroid biologically.     

Effect of 24-Epibrassinolide on Chlorophyll Fluorescence and Photosynthetic CO<Subscript>2</Subscript> Assimilation in <Emphasis Type="Italic">Vicia faba</Emphasis> Plants Treated with the Photosynthesis-Inhibiting Herbicide Terbutryn

Simultaneous measurements of chlorophyll (Chl) fluorescence and CO₂ assimilation (A) in Vicia faba leaves were taken during the first weeks of growth to evaluate the protective effect of 24-epibrassinolide (EBR) against damage caused by the application of the herbicide terbutryn (Terb) at pre-emergence. V. faba seeds were incubated for 24 h in EBR solutions (2 × 10⁻⁶ or 2 × 10⁻⁵ mM) and immediately sown. Terb was applied at recommended doses (1.47 or 1.96 kg ha⁻¹) at pre-emergence. The highest dose of Terb strongly decreased CO₂ assimilation, the maximum quantum yield of PSII photochemistry in the dark-adapted state (F _V/F _M), the nonphotochemical quenching (NPQ), and the effective quantum yield (ΔF/F′_M) during the first 3–4 weeks after plant emergence. Moreover, Terb increased the basal quantum yield of nonphotochemical processes (F ₀/F _M)_, the degree of reaction center closure (1 − q _p), and the fraction of light absorbed in PSII antennae that was dissipated via thermal energy dissipation in the antennae (1 − F′_V/F′_M). The herbicide also significantly reduced plant growth at the end of the experiment as well as plant length, dry weight, and number of leaves. The application of EBR to V. faba seeds before sowing strongly diminished the effect of Terb on fluorescence parameters and CO₂ assimilation, which recovered 13 days after plant emergence and showed values similar to those of control plants. The protective effect of EBR on CO₂ assimilation was detected at a photosynthetic photon flux density (PFD) of 650 μmol m⁻² s⁻¹ and the effect on ΔF/F′_M and photosynthetic electron transport (J) was detected under actinic lightings up to 1750 μmol m⁻² s⁻¹. The highest dose of EBR also counteracted the decrease in plant growth caused by Terb, and plants registered the same growth values as controls.     

Assessment of candidate reference genes for the expression studies with brassinosteroids in Lolium perenne and Triticum aestivum

Quantitative PCR studies need proper reference genes with expression stability exclusively validated under certain experimental conditions. The expression stability of several genes commonly used as references was tested under 24-epibrassinolide (EBR) and temperature treatment. Different statistical approaches (qBase^PLUS, BestKeeper, NormFinder) were used to prepare rankings of expression stability in two species of an economic importance: common wheat (Triticum aestivum) and perennial ryegrass (Lolium perenne). Candidate reference genes were shown to be regulated differentially in these two plant species. The maximum stability values indicated that the expression stability was higher in T. aestivum. Taking into account of all ranks it seems that TBP-1 and UBI in ryegrass and ACT, ADP and EF1A in wheat should be used as reference genes in the brassinosteroids and temperature involving studies.     

Cross-regulatory mechanisms in hormone signaling

Recent studies suggest that hormones act through a web of interacting responses rather than through isolated linear pathways. This signal integration architecture may be one mechanism for increasing the specificity of outcomes in different cellular contexts. Several common themes for cross-regulation between pathways can be observed. Here, we propose a classification scheme for different levels of signaling pathway cross-regulation. This scheme is based on which parts of the individual pathways are acting as information conduits between pathways. Examples from the recent plant hormone biology literature are used to illustrate the different modes of interaction. K. T. Kuppusamy and C. L. Walcher—co-first-authors.