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At least 289 records · Page 16Linked to original sources
PubMed2006

Opposite root growth phenotypes of hy5 versus hy5 hyh mutants correlate with increased constitutive auxin signaling.

The Arabidopsis transcription factor HY5 controls light-induced gene expression downstream of photoreceptors and plays an important role in the switch of seedling shoots from dark-adapted to light-adapted development. In addition, HY5 has been implicated in plant hormone signaling, accounting for the accelerated root system growth phenotype of hy5 mutants. Mutants in the close HY5 homolog HYH resemble wild-type, despite the largely similar expression patterns and levels of HY5 and HYH, and the functional equivalence of the respective proteins. Moreover, the relative contribution of HYH to the overall activity of the gene pair is increased by an alternative HYH transcript, which encodes a stabilized protein. Consistent with the enhanced root system growth observed in hy5 loss-of-function mutants, constitutively overexpressed alternative HYH inhibits root system growth. Paradoxically, however, in double mutants carrying hy5 and hyh null alleles, the hy5 root growth phenotype is suppressed rather than enhanced. Even more surprisingly, compared to wild-type, root system growth is diminished in hy5 hyh double mutants. In addition, the double mutants display novel shoot phenotypes that are absent from either single mutant. These include cotyledon fusions and defective vasculature, which are typical for mutants in genes involved in the transcriptional response to the plant hormone auxin. Indeed, many auxin-responsive and auxin signaling genes are misexpressed in hy5 mutants, and at a higher number and magnitude in hy5 hyh mutants. Therefore, auxin-induced transcription is constitutively activated at different levels in the two mutant backgrounds. Our data support the hypothesis that the opposite root system phenotypes of hy5 single and hy5 hyh double mutants represent the morphological response to a quantitative gradient in the same molecular process, that is gradually increased constitutive auxin signaling. The data also suggest that HY5 and HYH are important negative regulators of auxin signaling amplitude in embryogenesis and seedling development.

Alternative Splicing↗
PubMed1998

The ARF family of transcription factors and their role in plant hormone-responsive transcription.

Auxin response factors or ARFs are a recently discovered family of transcription factors that bind with specificity to auxin response elements (AuxREs) in promoters of primary or early auxin-responsive genes. ARFs have an amino-terminal DNA-binding domain related to the carboxyl-terminal DNA-binding domain in the maize transactivator VIVIPAROUS1. All but one ARF identified to date contain a carboxyl-terminal protein-protein interaction domain that forms a putative amphipathic alpha-helix. A similar carboxyl-terminal protein-protein interaction domain is found in the Aux/IAA class of auxin-inducible proteins. Some ARFs contain transcriptional activation domains, while others contain repression domains. ARFs appear to play a pivotal role in auxin-regulated gene expression of primary response genes.

Arabidopsis↗
PubMedDate not supplied

[Realization of the morphogenetic potential of plants: hormonal-genetic approach].

The basic principles of a model describing the hormonal control of the genome expression are stated, and its graphical interpretation is presented. The expression and evolution of the genetic information of organisms are regarded as an universal process of redifferentiation. The possibility is considered to represent the genome as a dynamic system. The study of the morphogenetic potential of organisms is based on the approach worked out by E. Cartan to the description of dynamic systems. A concept of morphogenetic potential is introduced, and its relation to genome states is shown. A mathematical model describing the expression of the morphogenetic potential is proposed. The mathematical formalism developed can be helpful for the solution of a great variety of tasks.

Gene Expression Regulation, Plant↗
PubMed1995

Unusual discrimination against carrier protein antibodies during partial purification of hapten-protein polyclonal antibodies to plant stress hormones.

Polyclonal antibodies (PcAb) were raised against t-zeatin riboside (t-ZR) and abscisic acid (ABA). t-ZR-BSA and ABA-BSA antibodies had high titre and specificity to haptens but also contained BSA specific antibodies as observed in double immuno diffusion and quantitative precipitation tests. Partial purification of antiserum by precipitation, desalting, and ion-exchange chromatography almost completely eliminated interference from BSA specific antibodies. Consequently, very little or no reaction was observed in dot-immunoblot assays even when high concentrations of BSA were probed with partially purified t-ZR-BSA IgG. Further studies with ABA antiserum showed that discrimination against BSA occurred during chromatography and not during salt fractionation. Because antibodies to both hapten and carrier protein were predominantly of IgG class, this unusual discrimination against carrier protein Ab was possibly influenced by two approaches followed for DEAE chromatography, viz. (i) adsorption of IgG at pH 8 followed by elution; or (ii) adsorption of contaminating proteins at neutral pH while specific IgG comes off as unbound fraction.

Abscisic Acid↗
PubMed2005

G protein signaling in the regulation of rice seed germination.

Seed germination and early seedling growth are regulated by an intricate network of hormonal signaling pathways. The plant hormones gibberellic acid (GA) and abscisic acid (ABA) are particularly important positive and negative regulators of these processes, respectively. In the cereal rice, mutant analysis has implicated heterotrimeric guanine nucleotide-binding protein (G protein) signaling in GA-stimulated expression of several genes, including expression of the gene encoding the hydrolytic enzyme alpha-amylase, which breaks down carbohydrate reserves and thus mobilizes nutrients that nourish the young seedling.

Arabidopsis↗
PubMed2006

Molecular mechanisms of ethylene signaling in Arabidopsis.

Ethylene is a gaseous plant hormone involved in several important physiological processes throughout a plant's life cycle. Decades of scientific research devoted to deciphering how plants are able to sense and respond to this key molecule have culminated in the establishment of one of the best characterized signal transduction pathways in plants. The ethylene signaling pathway starts with the perception of this gaseous hormone by a family of membrane-anchored receptors followed by a Raf-like kinase CTR1 that is physically associated with the receptors and actively inhibits downstream components of the pathway. A major gap is represented by the mysterious plant protein EIN2 that genetically works downstream of CTR1 and upstream of the key transcription factor EIN3. Transcriptional regulation by EIN3 and EIN3-family members has emerged as a key aspect of ethylene responses. The major components of this transcriptional cascade have been characterized and the involvement of post-transcriptional control by ubiquitination has been determined. Nevertheless, many aspects of this pathway still remain unknown. Recent genomic studies aiming to provide a more comprehensive view of modulation of gene expression have further emphasized the ample role of ethylene in a myriad of cellular processes and particularly in its crosstalk with other important plant hormones. This review aims to serve as a guide to the main scientific discoveries that have shaped the field of ethylene biology in the recent years.

Arabidopsis↗
PubMed1992

Past and present studies with ponasterones, the first insect molting hormones from plants.

The search for antitumor compounds from Southeast Asian plants led to ponasterones, the first phytoecdysteroids, just a year after structure determination of ecdysone and 20-hydroxyecdysone. An independent study of Chinese herb constituents by Takemoto et al. at Tohoku University led to the simultaneous and totally independent discovery of phytoecdysteroids. These findings greatly facilitated research in insect and crustacean physiology. The original structural studies on various phytoecdysteroids have led to interdisciplinary bioorganic studies in the area related to ecdysone receptor, ecdysone biosynthetic precursor (or its storage form), crustacean molt inhibitory factors, and so on.

Animals↗
PubMed1999

The tomato DWARF enzyme catalyses C-6 oxidation in brassinosteroid biosynthesis.

Brassinosteroids (BRs) are steroidal plant hormones essential for normal plant growth and development. Mutants in the biosynthesis or perception of BRs are usually dwarf. The tomato Dwarf gene (D), which was predicted to encode a cytochrome P450 enzyme (P450) with homology to other P450s involved in BR biosynthesis, was cloned previously. Here, we show that DWARF catalyses the C-6 oxidation of 6-deoxocastasterone (6-deoxoCS) to castasterone (CS), the immediate precursor of brassinolide. To do this, we first confirmed that the D cDNA complemented the mutant light- and dark-grown phenotypes of the extreme dwarf (dx) allele of tomato. To identify a substrate for the DWARF enzyme, exogenous application of BR intermediates to dx plants was carried out. C-6 oxoBR intermediates enhanced hypocotyl elongation whereas the C-6 deoxoBR, 6-deoxoCS, had little effect. Quantitative analysis of endogenous BR levels in tomato showed mainly the presence of 6-deoxoBRs. Furthermore, dx plants were found to lack CS and had a high level of 6-deoxoCS in comparison to D plants that had CS and a lower level of 6-deoxoCS. Confirmation that DWARF catalyzed the C-6 oxidation of 6-deoxoCS to CS was obtained by functional expression of DWARF in yeast. In these experiments, the intermediate 6alpha-hydroxycastasterone was identified, indicating that DWARF catalyzes two steps in BR biosynthesis. These data show that DWARF is involved in the C-6 oxidation in BR biosynthesis.

Journal Article↗
PubMed2006

Immunophilin-like TWISTED DWARF1 modulates auxin efflux activities of Arabidopsis P-glycoproteins.

The immunophilin-like protein TWISTED DWARF1 (TWD1/FKBP42) has been shown to physically interact with the multidrug resistance/P-glycoprotein (PGP) ATP-binding cassette transporters PGP1 and PGP19 (MDR1). Overlapping phenotypes of pgp1/pgp19 and twd1 mutant plants suggested a positive regulatory role of TWD1 in PGP-mediated export of the plant hormone auxin, which controls plant development. Here, we provide evidence at the cellular and plant levels that TWD1 controls PGP-mediated auxin transport. twd1 and pgp1/pgp19 cells showed greatly reduced export of the native auxin indole-3-acetic acid (IAA). Constitutive overexpression of PGP1 and PGP19, but not TWD1, enhanced auxin export. Coexpression of TWD1 and PGP1 in yeast and mammalian cells verified the specificity of the regulatory effect. Employing an IAA-specific microelectrode demonstrated that IAA influx in the root elongation zone was perturbed and apically shifted in pgp1/pgp19 and twd1 roots. Mature roots of pgp1/pgp19 and twd1 plants revealed elevated levels of free IAA, which seemed to account for agravitropic root behavior. Our data suggest a novel mode of PGP regulation via FK506-binding protein-like immunophilins, implicating possible alternative strategies to overcome multidrug resistance.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2004

Plant perceptions of plant growth-promoting Pseudomonas.

Plant-associated Pseudomonas live as saprophytes and parasites on plant surfaces and inside plant tissues. Many plant-associated Pseudomonas promote plant growth by suppressing pathogenic micro-organisms, synthesizing growth-stimulating plant hormones and promoting increased plant disease resistance. Others inhibit plant growth and cause disease symptoms ranging from rot and necrosis through to developmental dystrophies such as galls. It is not easy to draw a clear distinction between pathogenic and plant growth-promoting Pseudomonas. They colonize the same ecological niches and possess similar mechanisms for plant colonization. Pathogenic, saprophytic and plant growth-promoting strains are often found within the same species, and the incidence and severity of Pseudomonas diseases are affected by environmental factors and host-specific interactions. Plants are faced with the challenge of how to recognize and exclude pathogens that pose a genuine threat, while tolerating more benign organisms. This review examines Pseudomonas from a plant perspective, focusing in particular on the question of how plants perceive and are affected by saprophytic and plant growth-promoting Pseudomonas (PGPP), in contrast to their interactions with plant pathogenic Pseudomonas. A better understanding of the molecular basis of plant-PGPP interactions and of the key differences between pathogens and PGPP will enable researchers to make more informed decisions in designing integrated disease-control strategies and in selecting, modifying and using PGPP for plant growth promotion, bioremediation and biocontrol.

Immunity, Innate↗
PubMed1998

Controlled cytokinin production in transgenic tobacco using a copper-inducible promoter

The cytokinin group of plant hormones regulates aspects of plant growth and development, including the release of lateral buds from apical dominance and the delay of senescence. In this work the native promoter of a cytokinin synthase gene (ipt) was removed and replaced with a Cu-controllable promoter. Tobacco (Nicotiana tabacum L. cv tabacum) transformed with this Cu-inducible ipt gene (Cu-ipt) was morphologically identical to controls under noninductive conditions in almost all lines produced. However, three lines grew in an altered state, which is indicative of cytokinin overproduction and was confirmed by a full cytokinin analysis of one of these lines. The in vitro treatment of morphologically normal Cu-ipt transformants with Cu2+ resulted in delayed leaf senescence and an increase in cytokinin concentration in the one line analyzed. In vivo, inductive conditions resulted in a significant release of lateral buds from apical dominance. The morphological changes seen during these experiments may reflect the spatial aspect of control exerted by this gene expression system, namely expression from the root tissue only. These results confirmed that endogenous cytokinin concentrations in tobacco transformants can be temporally and spatially controlled by the induction of ipt gene expression through the Cu-controllable gene-expression system.

Journal Article↗