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PubMed2006

[Plant mechanism of an adaptive stress response homologous to bacterial stringent response].

All living organisms possess adaptive responses to environmental stresses that are essential to ensuring cell survival. One of them is the stringent response, initially discovered forty years ago in the gram-negative model organism E. coli. Recently plant homologues to the bacterial relA/spoT genes were identified (RSH genes--RelA/SpoT Homologues). Also the products of rsh proteins activity--(p)ppGpp were identified in the chloroplasts of plant cells. Levels of ppGpp increased markedly when plants were subjected to some biotic and abiotic stresses. Elevation of ppGpp levels was elicited also by treatment with plant hormones. What is more--in vitro, chloroplast RNA polymerase activity was inhibited in the presence of ppGpp. It is supposed that plant stringent response is a conserve stress-response pathway possibly operating via regulation of chloroplast gene expression and, thus, the regulation of plastid metabolism.

Adaptation, Physiological↗
PubMed2004

OsPIPK 1, a rice phosphatidylinositol monophosphate kinase, regulates rice heading by modifying the expression of floral induction genes.

A rice gene, OsPIPK 1, encoding a 792-aa putative phosphatidylinositol 4-phosphate 5-kinase (PIPK), was identified and characterized. Comparison between the cDNA and genomic sequences revealed the presence of 10 exons (39-1050 bp) and 9 introns (88-745 bp) in OsPIPK 1 gene. The deduced amino acid sequence of OsPIPK1 contains a lipid kinase domain that is highly homologous to those of previously isolated PIPKs, and structural analysis revealed the intriguing presence of multiple MORN motifs at the N-terminus. The MORN motifs have also been detected in PIPKs from Arabidopsis thaliana and Oryza sativa, but not in the well-characterized PIPKs from animal and yeast cells. RT-PCR analysis indicated that OsPIPK 1 was expressed almost constitutively in roots, shoots, stems, leaves and flowers, and up-regulated following treatment with plant hormones or application of various stresses. An antisense transgenic strategy was used to suppress the expression of OsPIPK 1, and homozygous transgenic plants showed earlier heading (7-14 days earlier) than control plants, suggesting that OsPIPK 1 negatively regulates floral initiation. This was further confirmed by morphologic observation showing earlier floral development in antisense plants, as well as leaf emergence measurement indicating delayed leaf development under OsPIPK 1 deficiency, a common phenotype observed with earlier flowering. RT-PCR analysis and cDNA chip technology were used to examine transcripts of various genes in the transgenic plants and the results showed altered transcriptions of several flowering-time or -identity related genes, suggesting that OsPIPK 1 is involved in rice heading through regulation of floral induction genes, signaling and metabolic pathways.

Amino Acid Motifs↗
PubMed2002

Apple 1-aminocyclopropane-1-carboxylate synthase in complex with the inhibitor L-aminoethoxyvinylglycine. Evidence for a ketimine intermediate.

The 1.6-A crystal structure of the covalent ketimine complex of apple 1-aminocyclopropane-1-carboxylate (ACC) synthase with the potent inhibitor l-aminoethoxyvinylglycine (AVG) is described. ACC synthase catalyzes the committed step in the biosynthesis of ethylene, a plant hormone that is responsible for the initiation of fruit ripening and for regulating many other developmental processes. AVG is widely used in plant physiology studies to inhibit the activity of ACC synthase. The structural assignment is supported by the fact that the complex absorbs maximally at 341 nm. These results are not in accord with the recently reported crystal structure of the tomato ACC synthase AVG complex, which claims that the inhibitor only associates noncovalently. The rate constant for the association of AVG with apple ACC synthase was determined by stopped-flow spectrophotometry (2.1 x 10(5) m(-1) s(-1)) and by the rate of loss of enzyme activity (1.1 x 10(5) m(-1) s(-1)). The dissociation rate constant determined by activity recovery is 2.4 x 10(-6) s(-1). Thus, the calculated K(d) value is 10-20 pm.

Amines↗
PubMed1998

Expression studies of the zeaxanthin epoxidase gene in nicotiana plumbaginifolia

Abscisic acid (ABA) is a plant hormone involved in the control of a wide range of physiological processes, including adaptation to environmental stress and seed development. In higher plants ABA is a breakdown product of xanthophyll carotenoids (C40) via the C15 intermediate xanthoxin. The ABA2 gene of Nicotiana plumbaginifolia encodes zeaxanthin epoxidase, which catalyzes the conversion of zeaxanthin to violaxanthin. In this study we analyzed steady-state levels of ABA2 mRNA in N. plumbaginifolia. The ABA2 mRNA accumulated in all plant organs, but transcript levels were found to be higher in aerial parts (stems and leaves) than in roots and seeds. In leaves ABA2 mRNA accumulation displayed a day/night cycle; however, the ABA2 protein level remained constant. In roots no diurnal fluctuation in mRNA levels was observed. In seeds the ABA2 mRNA level peaked around the middle of development, when ABA content has been shown to increase in many species. In conditions of drought stress, ABA levels increased in both leaves and roots. A concomitant accumulation of ABA2 mRNA was observed in roots but not in leaves. These results are discussed in relation to the role of zeaxanthin epoxidase both in the xanthophyll cycle and in the synthesis of ABA precursors.

Journal Article↗
PubMed1987

Auxin production by plant-pathogenic pseudomonads and xanthomonads.

Pathogenic strains of Xanthomonas campestris pv. glycines which cause hypertrophy of leaf cells of susceptible soybean cultivars and nonpathogenic strains which do not cause hypertrophy were compared for their ability to produce indole compounds, including the plant hormone indole-3-acetic acid (IAA) in liquid media with or without supplementation with l-tryptophan. Several additional strains of plant-pathogenic xanthomonads and pseudomonads were also tested for IAA production to determine whether in vitro production of IAA is related to the ability to induce hypertrophic growth of host tissues. Indoles present in culture filtrates were identified by thin-layer chromatography, high-performance liquid chromatography, UV spectroscopy, mass spectroscopy, and gas chromatography-mass spectrometry and were quantitated by high-performance liquid chromatography. All strains examined produced IAA when liquid media were supplemented with l-tryptophan. The highest levels of IAA were found in culture filtrates from the common bean pathogen Pseudomonas syringae pv. syringae, and this was the only bacterium tested which produced IAA without addition of tryptophan to the medium. Additional indoles identified in culture filtrates of the various strains included indole-3-lactic acid, indole-3-aldehyde, indole-3-acetamide, and N-acetyltryptophan. Pseudomonads and xanthomonads could be distinguished by the presence of N-acetyltryptophan, which was found only in xanthomonad culture filtrates.

Journal Article↗
PubMed2000

1-aminocyclopropane-1-carboxylate (ACC) deaminase induced by ACC synthesized and accumulated in Penicillium citrinum intracellular spaces.

We have already described how 1-aminocyclopropane-1-carboxylic acid (ACC), which is a precursor of the plant hormone ethylene, is synthesized in Penicillium citrinum through the same reaction by the catalysis of ACC synthase [EC 4.4.1.14] as in higher plants. In addition, ACC deaminase [EC 4.1.99.4], which degrades ACC to 2-oxobutyrate and ammonia, was also purified from this strain. To study control of induction of ACC deaminase in this organism, we have isolated and analyzed the cDNA of P. citrinum ACC deaminase and studied the expression of ACC deaminase mRNA in P. citrinum cells. By the analysis of peptides from the digests of the purified and modified ACC deaminase with lysylendopeptidase, 70 % of its amino acid sequences were obtained. These amino acid sequences were used to identify a cDNA, consisting of 1,233 bp with an open reading frame of 1,080 bp encoding ACC deaminase with 360 amino acids. The deduced amino acids from the cDNA are identical by 52% and 45% to those of enzymes of Pseudomonas sp. ACP and Hansenula saturnus. Through Northern blot analysis, we found that the mRNA of ACC deaminase was expressed in P. citrinum cells grown in a medium containing 0.05% L-methionine. These findings suggest that ACC synthesized by ACC synthase and accumulated in P. citrinum intracellular spaces can induce the ACC deaminase that degrades the ACC.

Amino Acid Sequence↗
PubMed1999

Increased steady state mRNA levels of the STM and KNAT1 homeobox genes in cytokinin overproducing Arabidopsis thaliana indicate a role for cytokinins in the shoot apical meristem.

This study investigates the consequences of endogenously enhanced biosynthesis of the plant hormone cytokinin in Arabidopsis thaliana (L.) Heynh. Transcriptional control of the bacterial ipt gene by the Drosophila melanogaster hsp70 promoter enabled temperature-dependent increased cytokinin production in transgenic plants. Heat-treated plants accumulated higher levels of unbound and bound zeatin-type cyto-kinins, the latter being preferentially N-conjugated glucosides. Cytokinin overproduction significantly increased the biomass of seedlings. Ipt transgenics had higher steady state mRNA levels of the shoot meristem specifying homeobox genes KNAT1 and STM, similar to the cytokinin-overproducing shoot meristem mutant amp1 (hpt, cop2, pt) This finding, together with previously described phenotypic similarities between transgenic cytokinin-overproducing plants and plants overexpressing the KNAT1 or KN1 genes, suggests that these factors act on the same pathway. We hypothesize that cytokinins act upstream of KNAT1 and STM. The influence of cytokinins on homeobox genes provides a link between the hormone and the developmental genes and indicates a role for cytokinins in the shoot apical meristem.

Alkyl and Aryl Transferases↗
PubMed2002

Changes in the activities of antioxidant enzymes in response to virus infection and hormone treatment.

Activities of enzymes involved in the detoxification of reactive oxygen species (catalase, glutathione reductase, peroxidase and superoxide dismutase (SOD)) were examined in the leaves of Phaseolus vulgaris L. var. Top Crop treated with plant hormones and infected with a non-lesion-forming isolate of white clover mosaic potexvirus (WClMV). The activities of catalase, glutathione reductase and SOD rapidly declined after infection while peroxidase activity was enhanced. These changes occurred before the rapid increase (5 days) in WClMV replication. A mild chlorosis appeared 7-10 days after inoculation but necrosis was never observed on inoculated leaves. Plants treated with dihydrozeatin, salicylic acid and jasmonic acid prior to WClMV inoculation showed elevated catalase, glutathione reductase, and peroxidase activity, while SOD activities remained the same as in water-treated controls. These treatments all inhibited virus replication with enzyme activities remaining near control levels. We propose that a decline in free radical scavenging capacity may be required before a rapid increase in virus replication can take place. Treatments increasing the ability of the plant to scavenge reactive oxygen species may hinder virus replication. A possible role for reactive oxygen species as a requirement for virus replication is discussed.

Journal Article↗
PubMed2006

Crosstalk between jasmonic acid, ethylene and Nod factor signaling allows integration of diverse inputs for regulation of nodulation.

Plant hormones interact at many different levels to form a network of signaling pathways connected by antagonistic and synergistic interactions. Ethylene and jasmonic acid both act to regulate the plant's responsiveness to a common set of biotic stimuli. In addition ethylene has been shown to negatively regulate the plant's response to the rhizobial bacterial signal, Nod factor. This regulation occurs at an early step in the Nod factor signal transduction pathway, at or above Nod factor-induced calcium spiking. Here we show that jasmonic acid also inhibits the plant's responses to rhizobial bacteria, with direct effects on Nod factor-induced calcium spiking. However, unlike ethylene, jasmonic acid not only inhibits spiking but also suppresses the frequency of calcium oscillations when applied at lower concentrations. This effect of jasmonic acid is amplified in the ethylene-insensitive mutant skl, indicating an antagonistic interaction between these two hormones for regulation of Nod factor signaling. The rapidity of the effects of ethylene and jasmonic acid on Nod factor signaling suggests direct crosstalk between these three signal transduction pathways. This work provides a model by which crosstalk between signaling pathways can rapidly integrate environmental, developmental and biotic stimuli to coordinate diverse plant responses.

Calcium↗
PubMed1989

Differential growth in plants--a phenomenon that occurs at all levels of organization.

Differential growth is a feature of cells, the organs which they construct and the whole plant itself. The control of differential growth at each of these three levels of organization resides in the level lower than that in which it is expressed. Thus, differential growth of cells is regulated by the patterns of intracellular microtubules and cellulose microfibrils of the walls, that of organs by the pattern of growth of their cells, and that of the organism by the relative rates of organ growth. The latter is, in turn, determined an all-pervading system of correlative interactions. Plant hormones by may play a role in each of these regulatory systems.

Plant Cells↗
PubMed2004

Gibberellin production by bacteria and its involvement in plant growth promotion and yield increase.

This review focuses on studies with bacteria for which biosynthesis/production of the plant hormones gibberellins have been demonstrated. Actual data on gibberellin metabolism by bacteria are analyzed in comparison with the biosynthetic pathways known for vascular plants and fungi. The potential involvement of gibberellins produced by symbiotic and soil-endophytic microorganisms in plant growth promotion and yield increase is also discussed.

Bacteria↗
PubMed1998

A higher plant seven-transmembrane receptor that influences sensitivity to cytokinins.

BACKGROUND: All organisms perceive and respond to a profusion of environmental and endogenous signals that influence growth, development and behavior. The G-protein signalling pathway is a highly conserved mechanism for transducing extracellular signals, and the superfamily of receptors that have seven transmembrane (7TM) domains is a primary element of this pathway. Evidence that heterotrimeric G proteins are involved in signal transduction in plants is accumulating, prompting speculation that plant 7TM receptors might exist. RESULTS: Using information in the dbEST database of expressed sequence tags, we isolated an Arabidopsis thaliana gene (GCR1) that encodes a protein with seven predicted membrane-spanning domains and other features characteristic of 7TM receptors. The protein shows 18-23% amino-acid identity (46-53% similarity) to, and good colinear alignment with, 7TM receptors from three different families. Its highest sequence identity is with the Dictyostelium cAMP receptors. GCR1 is expressed at very low levels in the roots, stems and leaves of Arabidopsis; it is a single-copy gene which maps close to the restriction fragment length polymorphism marker m291 on chromosome 5. Transgenic Arabidopsis expressing antisense GCR1 under the control of the constitutive cauliflower mosaic virus 35S promoter have reduced sensitivity to cytokinins in roots and shoots, yet respond normally to all other plant hormones. This suggests a functional role for GCR1 in cytokinin signal transduction. CONCLUSIONS: GCR1 encodes the first 7TM receptor homologue identified in higher plants and is involved in cytokinin signal transduction. This discovery suggests that 7TM receptors are ancient and predate the divergence of plants and animals.

Arabidopsis↗
PubMed2002

The WUSCHEL gene promotes vegetative-to-embryonic transition in Arabidopsis.

Formation of somatic embryos in plants is known to require high concentrations of auxin or 2,4-dichlorophenoxyacetic acid (2,4-D), which presumably acts to trigger a signalling cascade. However, very little is known about the molecular mechanism that mediates the vegetative-to-embryogenic transition. We have employed a genetic approach to dissect the signal transduction pathway during somatic embryogenesis. In a functional screen using a chemical-inducible activation-tagging system, we identified two alleles of Arabidopsis gene PGA6 whose induced overexpression caused high-frequency somatic embryo formation in all tissues and organs tested, without any external plant hormones. Upon inducer withdrawal, all these somatic embryos were able to germinate directly, without any further treatment, and to develop into fertile adult plants. PGA6 was found to be identical to WUSCHEL (WUS), a homeodomain protein previously shown to be involved in specifying stem cell fate in shoot and floral meristems. Transgenic plants carrying an estradiol-inducible XVE-WUS transgene can phenocopy pga6-1 and pga6-2. Our results suggest that WUS/PGA6 also plays a key role during embryogenesis, presumably by promoting the vegetative-to-embryogenic transition and/or maintaining the identity of the embryonic stem cells.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2006

Crystal structure of 12-oxophytodienoate reductase 3 from tomato: self-inhibition by dimerization.

12-Oxophytodienoate reductase (OPR) 3, a homologue of old yellow enzyme (OYE), catalyzes the reduction of 9S,13S-12-oxophytodienoate to the corresponding cyclopentanone, which is subsequently converted to the plant hormone jasmonic acid (JA). JA and JA derivatives, as well as 12-oxophytodienoate and related cyclopentenones, are known to regulate gene expression in plant development and defense. Together with other oxygenated fatty acid derivatives, they form the oxylipin signature in plants, which resembles the pool of prostaglandins in animals. Here, we report the crystal structure of OPR3 from tomato and of two OPR3 mutants. Although the catalytic residues of OPR3 and related OYEs are highly conserved, several characteristic differences can be discerned in the substrate-binding regions, explaining the remarkable substrate stereoselectivity of OPR isozymes. Interestingly, OPR3 crystallized as an extraordinary self-inhibited dimer. Mutagenesis studies and biochemical analysis confirmed a weak dimerization of OPR3 in vitro, which correlated with a loss of enzymatic activity. Based on structural data of OPR3, a putative mechanism for a strong and reversible dimerization of OPR3 in vivo that involves phosphorylation of OPR3 is suggested. This mechanism could contribute to the shaping of the oxylipin signature, which is critical for fine-tuning gene expression in plants.

Amino Acid Sequence↗
PubMed2004

Brassinosteroids do not undergo long-distance transport in pea. Implications for the regulation of endogenous brassinosteroid levels.

It is widely accepted that brassinosteroids (BRs) are important regulators of plant growth and development. However, in comparison to the other classical plant hormones, such as auxin, relatively little is known about BR transport and its potential role in the regulation of endogenous BR levels in plants. Here, we show that end-pathway BRs in pea (Pisum sativum) occur in a wide range of plant tissues, with the greatest accumulation of these substances generally occurring in the young, actively growing tissues, such as the apical bud and young internodes. However, despite the widespread distribution of BRs throughout the plant, we found no evidence of long-distance transport of these substances between different plant tissues. For instance, we show that the maintenance of steady-state BR levels in the stem does not depend on their transport from the apical bud or mature leaves. Similarly, reciprocal grafting between the wild type and the BR-deficient lkb mutants demonstrates that the maintenance of steady-state BR levels in whole shoots and roots does not depend on either basipetal or acropetal transport of BRs between these tissues. Together, with results from (3)H-BR feeding studies, these results demonstrate that BRs do not undergo long-distance transport in pea. The widespread distribution of end-pathway BRs and the absence of long-distance BR transport between different plant tissues provide significant insight into the mechanisms that regulate BR homeostasis in plants.

Biological Transport↗
PubMed2003

The effect of selenium on the accumulation of some metals in Zea mays L. plants treated with indole-3-acetic acid.

In this study, we examined the relationship between the accumulation of NaHSeO3, the plant hormone (IAA), and some nutrient elements (K(+), Na(+), Ca(2+)) in the tissues of the roots, mesocotyls and leaves of Zea mays L. plants. Our experiments were carried out with eight- to nine-day old maize plants (Zea mays L. var K33xF2) grown on Hoagland's medium containing the standard macro- and microelements, IAA and NaHSeO(3). The accumulation of selenium, potassium, sodium and calcium in the seedlings was measured by emission spectroscopy using a spectrometer with excitation by the argon inductively coupled plasma technique (ICP-AES). We observed that when selenite and phytohormone (IAA) are present in the external medium of growing plants, they change the uptake and accumulation of some cations (K(+), Na(+), Ca(2+)) in the leaf, mesocotyl and root tissues. The change of transport of some nutrient elements is probably one of the first observed symptoms of selenium's effects on plants.

Calcium↗
PubMed2004

Ethylene synthesis and sensitivity in crop plants.

Closed and semi-closed plant growth chambers have long been used in studies of plant and crop physiology. These studies include the measurement of photosynthesis and transpiration via photosynthetic gas exchange. Unfortunately, other gaseous products of plant metabolism can accumulate in these chambers and cause artifacts in the measurements. The most important of these gaseous byproducts is the plant hormone ethylene (C2H4). In spite of hundreds of manuscripts on ethylene, we still have a limited understanding of the synthesis rates throughout the plant life cycle. We also have a poor understanding of the sensitivity of intact, rapidly growing plants to ethylene. We know ethylene synthesis and sensitivity are influenced by both biotic and abiotic stresses, but such whole plant responses have not been accurately quantified. Here we present an overview of basic studies on ethylene synthesis and sensitivity.

Amino Acids, Cyclic↗
PubMed1995

An ethylene-inducible component of signal transduction encoded by never-ripe.

The ripening-impaired tomato mutant Never-ripe (Nr) is insensitive to the plant hormone ethylene. The gene that cosegregates with the Nr locus encodes a protein with homology to the Arabidopsis ethylene receptor ETR1 but is lacking the response regulator domain found in ETR1 and related prokaryotic two-component signal transducers. A single amino acid change in the sensor domain confers ethylene insensitivity when expressed in transgenic tomato plants. Modulation of NR gene expression during fruit ripening controls response to the hormone ethylene.

Amino Acid Sequence↗