bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of PEAM4, the pea AP1 functional homologue, supports a model for AP1‐like genes controlling both floral meristem and floral organ identity in different plant species
Authors: Berbel Ana , Navarro Cristina , Ferrándiz Cristina , Cañas Luis Antonio , Madueño Francisco , Beltrán José‐Pío 
Published: March 2003

Summary APETALA1 (AP1) and its homologue SQUAMOSA (SQUA) are key regulatory genes specifying floral meristem identity in the model plants Arabidopsis and Antirrhinum. Despite many similarities in their sequence, expression and functions, only AP1 appears to have the additional role of specifying sepal and petal identity. No true AP1/SQUA‐functional homologues from any other plant species have been functionally studied in detail, therefore the question of how the different functions of AP1‐like genes are conserved between species has not been addressed. We have isolated and characterized PEAM4, the AP1/SQUA‐functional homologue from pea, a plant with a different floral morphology and inflorescence architecture to that of Arabidopsis or Antirrhinum. PEAM4 encodes for a polypeptide 76% identical to AP1, but lacks the C‐terminal prenylation motif, common to AP1 and SQUA, that has been suggested to control the activity of AP1. Nevertheless, constitutive expression of PEAM4 caused early flowering in tobacco and Arabidopsis. In Arabidopsis, PEAM4 also caused inflorescence‐to‐flower transformations similar to constitutive AP1 expression, and was able to rescue the floral organ defects of the strong ap1‐1 mutant. Our results suggest that the control of both floral meristem and floral organ identity by AP1 is not restricted to Arabidopsis, but is extended to species with diverse floral morphologies, such as pea.
Single guard cell recordings in intact plants: light‐induced hyperpolarization of the plasma membrane
Authors: Roelfsema M. Rob G. , Steinmeyer Ralf , Staal Marten , Hedrich Rainer 
Published: March 2003

SummaryGuard cells are electrically isolated from other plant cells and therefore offer the unique possibility to conduct current‐ and voltage‐clamp recordings on single cells in an intact plant. Guard cells in their natural environment were impaled with double‐barreled electrodes and found to exhibit three physiological states. A minority of cells were classified as far‐depolarized cells. These cells exhibited positive membrane potentials and were dominated by the activity of voltage‐dependent anion channels. All other cells displayed both outward and inward rectifying K+‐channel activity. These cells were either depolarized or hyperpolarized, with average membrane potentials of −41 mV (SD 16) and −112 mV (SD 19), respectively. Depolarized guard cells extrude K+ through outward rectifying channels, while K+ is taken up via inward rectifying channels in hyperpolarized cells. Upon a light/dark transition, guard cells that were hyperpolarized in the light switched to the depolarized state. The depolarization was accompanied by a 35 pA decrease in pump current and an increase in the conductance of inward rectifying channels. Both an increase in pump current and a decrease in the conductance of the inward rectifier were triggered by blue light, while red light was ineffective. From these studies we conclude that light modulates plasma membrane transport through large membrane potential changes, reversing the K+‐efflux via outward rectifying channels to a K+‐influx via inward rectifying channels.
A novel gene mutation that confers abnormal patterns of β‐carotene accumulation in cauliflower (Brassica oleracea var. botrytis)
Authors: Li Li , Paolillo Dominick J. , Parthasarathy Mandayam V. , DiMuzio Elena M. , Garvin David F. 
Published: March 2003

SummaryThe Or gene of cauliflower (Brassica oleracea var. botrytis) causes many tissues of the plant to accumulate carotenoids and turn orange, which is suggestive of a perturbation of the normal regulation of carotenogenesis. A series of experiments to explore the cellular basis of the carotenoid accumulation induced by the Or gene was completed. The Or gene causes obvious carotenoid accumulation in weakly or unpigmented tissues such as the curd, pith, leaf bases and shoot meristems, and cryptically in some cells of other organs, including the roots and developing fruits. The dominant carotenoid accumulated is β‐carotene, which can reach levels that are several hundred‐fold higher than those in comparable wild‐type tissues. The β‐carotene accumulates in plastids mainly as a component of massive, highly ordered sheets. The Or gene does not affect carotenoid composition of leaves, nor does it alter color and chromoplast appearance in flower petals. Interestingly, mRNA from carotenogenic and other isoprenoid biosynthetic genes upstream of the carotenoid pathway was detected both in orange tissues of the mutant, and in comparable unpigmented wild‐type tissues. Thus the unpigmented wild‐type tissues are likely to be competent to synthesize carotenoids, but this process is suppressed by an unidentified mechanism. Our results suggest that the Or gene may induce carotenoid accumulation by initiating the synthesis of a carotenoid deposition sink in the form of the large carotenoid‐sequestering sheets.
Overexpression of DWARF4 in the brassinosteroid biosynthetic pathway results in increased vegetative growth and seed yield in Arabidopsis
Authors: Choe Sunghwa , Fujioka Shozo , Noguchi Takahiro , Takatsuto Suguru , Yoshida Shigeo , Feldmann Kenneth A. 
Published: March 2003

SummaryPlants unable to synthesize or perceive brassinosteroids (BRs) are dwarfs. Arabidopsis dwf4 was shown to be defective in a steroid 22α hydroxylase (CYP90B1) step that is the putative rate‐limiting step in the BR biosynthetic pathway. To better understand the role of DWF4 in BR biosynthesis, transgenic Arabidopsis plants ectopically overexpressing DWF4 (AOD4) were generated, using the cauliflower mosaic virus 35S promoter, and their phenotypes were characterized. The hypocotyl length of both light‐ and dark‐grown AOD4 seedlings was increased dramatically as compared to wild type. At maturity, inflorescence height increased >35% in AOD4 lines and >14% in tobacco DWF4 overexpressing lines (TOD4), relative to controls. The total number of branches and siliques increased more than twofold in AOD4 plants, leading to a 59% increase in the number of seeds produced. Analysis of endogenous BR levels in dwf4, Ws‐2 and AOD4 revealed that dwf4 accumulated the precursors of the 22α‐hydroxylation steps, whereas overexpression of DWF4 resulted in increased levels of downstream compounds relative to Ws‐2, indicative of facilitated metabolic flow through the step. Both the levels of DWF4 transcripts and BR phenotypic effects were progressively increased in dwf4, wild‐type and AOD4 plants, respectively. This suggests that it will be possible to control plant growth by engineering DWF4 transcription in plants.
Involvement of a novel Arabidopsis phospholipase D, AtPLDδ, in dehydration‐inducible accumulation of phosphatidic acid in stress signalling
Authors: Katagiri Takeshi , Takahashi Seiji , Shinozaki Kazuo 
Published: March 2003

SummaryPhospholipid metabolism is involved in plant responses to drought and salinity stress. To investigate the role of phospholipase D (PLD) and its product phosphatidic acid (PtdOH) in stress signalling, we isolated a novel PLD cDNA, designated AtPLDδ, by screening a cDNA library prepared from dehydrated Arabidopsis thaliana. The AtPLDδ protein, of 868 amino acids, has a putative catalytic domain and a C2 domain that is involved in Ca2+/phospholipid binding. The AtPLDδ mRNA accumulated in response to dehydration and high salt stress. Histochemical analysis showed that the AtPLDδ gene is strongly expressed in the vascular tissues of cotyledons and leaves under dehydration stress conditions. Under normal growth conditions, AtPLDδ was expressed in roots, leaves, stems and flowers but not in siliques. We showed that dehydration stimulates the accumulation of PtdOH. The accumulation of PtdOH in response to dehydration was significantly suppressed in AtPLDδ antisense transgenic plants. These results suggest that AtPLDδ may be involved in PtdOH accumulation in the dehydration stress response.
Localization of flavonoid enzymes in Arabidopsis roots
Authors: Saslowsky David , Winkel‐Shirley Brenda 
Published: March 2003

SummaryImmunofluorescence and immuno‐electron microscopy have been used to test the hypothesis that flavonoid metabolism is organized as a membrane‐associated enzyme complex. The cellular and subcellular locations of chalcone synthase (CHS) and chalcone isomerase (CHI), the first two enzymes of this pathway, were examined in Arabidopsis roots. High levels of both enzymes were found in the epidermal and cortex cells of the elongation zone and the root tip, consistent with the accumulation of flavonoid endproducts at these sites. Co‐localization of CHS and CHI was observed at the endoplasmic reticulum and tonoplast in these cells, and also in electron‐dense regions that are, as yet, unidentified. In addition, a striking asymmetric distribution was observed for these enzymes in cortex cells of the elongation zone, which may provide clues about the physiological function of flavonoids in roots. The accumulation of CHS and CHI was also examined in tt7(88), a mutant in the gene for flavonoid 3′‐hydroxylase (F3′H), which has been postulated to serve as a membrane anchor for the flavonoid enzyme complex. CHS and CHI accumulated to lower levels in cortex cells and higher levels in epidermal cells in the roots of this mutant as compared with wild‐type plants. Moreover, the electron‐dense regions containing these two enzymes were not observed. However, localization of CHS and CHI to the ER and tonoplast did not appear to be affected, suggesting that other proteins may function in recruiting the ‘soluble’ flavonoid enzymes to membranes. Staining of flavonoid endproducts with DPBA was consistent with expression of CHS and CHI in these seedlings.
Development and commercial use of Bollgard®cotton in the USA – early promises versus today's reality
Authors: Perlak Frederick J. , Oppenhuizen Mark , Gustafson Karen , Voth Richard , Sivasupramaniam Saku , Heering David , Carey Boyd , Ihrig Robert A. , Roberts James K. 
Published: March 2003

SummaryBollgard®cotton is the trademark given to a number of varieties of cotton bio‐engineered to produce an insecticidal protein fromBacillus thuringiensis(Bt). When produced by the modified cotton plants, this protein controls certain lepidopterous cotton insect pests. Commercially available since 1996, these cotton varieties are purchased under a license agreement in which the growers pay a fee and agree to abide by the terms, which include a 1‐year license to use the technology and agreement to participate in an insect resistance management program. Today, Bollgard®cotton is grown on more than one‐third of all cotton acreage in the USA. This product has reduced cotton production costs and insecticide use by providing an effective alternative to chemical insecticides for the control of tobacco budworm,Heliothis virescens;cotton bollworm,Helicoverpa zea;and pink bollworm,Pectinophora gossypiella. The specificity and safety profile of the Bt protein producedin plantain cotton was maintained. It has retained its selectivity for lepidopterous insects and lacks the characteristics found in potential allergenic proteins. Fiber quality, the agronomic characteristics of the plant and seed composition remain unchanged. New cotton technology is being developed to provide improved insect control and a wider spectrum of activity. These future products could further reduce insecticide use in the production of cotton, while maintaining the high level of safety and reliability that has been demonstrated by five seasons of Bollgard®cotton use.
The strawberry FaMYB1 transcription factor suppresses anthocyanin and flavonol accumulation in transgenic tobacco
Authors: Aharoni Asaph , De Vos C. H. Ric , Wein Martina , Sun Zhongkui , Greco Raffaella , Kroon Arthur , Mol Joseph N. M. , O'Connell Ann P. 
Published: March 2003

SummaryFruit ripening is characterized by dramatic changes in gene expression, enzymatic activities and metabolism. Although the process of ripening has been studied extensively, we still lack valuable information on how the numerous metabolic pathways are regulated and co‐ordinated. In this paper we describe the characterization of FaMYB1, a ripening regulated strawberry gene member of the MYB family of transcription factors. Flowers of transgenic tobacco lines overexpressing FaMYB1 showed a severe reduction in pigmentation. A reduction in the level of cyanidin 3‐rutinoside (an anthocyanin) and of quercetin‐glycosides (flavonols) was observed. Expression of late flavonoid biosynthesis genes and their enzyme activities were aversely affected by FaMYB1 overexpression. Two‐hybrid assays in yeast showed that FaMYB1 could interact with other known anthocyanin regulators, but it does not act as a transcriptional activator. Interestingly, the C‐terminus of FaMYB1 contains the motif pdLNLD/ELxiG/S. This motif is contained in a region recently proposed to be involved in the repression of transcription by AtMYB4, an Arabidopsis MYB protein. Our results suggest that FaMYB1 may play a key role in regulating the biosynthesis of anthocyanins and flavonols in strawberry. It may act to repress transcription in order to balance the levels of anthocyanin pigments produced at the latter stages of strawberry fruit maturation, and/or to regulate metabolite levels in various branches of the flavonoid biosynthetic pathway.
A role for salicylic acid and NPR1 in regulating cell growth in Arabidopsis
Authors: Vanacker Hélène , Lu Hua , Rate Debra N. , Greenberg Jean T. 
Published: March 2003

SummarySalicylic acid (SA) plays a key role in activating defenses and cell death during plant–pathogen interactions. In response to some pathogens, SA also limits the extent of cell death, indicating that it acts positively or negatively depending on the host–pathogen interaction. In addition, we previously showed that SA affects cell growth in the Arabidopsis defense‐related mutants accelerated cell death 6–1 (acd6–1) and aberrant growth and death 2 (agd2). Using acd6–1, agd2 and two other defense‐related mutants, lesion simulating disease 6 (lsd6), suppressor of SA‐insensitivity (ssi1), we show here in detail that SA regulates cell growth by specifically affecting cell enlargement, endoreduplication and/or cell division. We find that SA can act either positively or negatively to regulate cell growth depending on the context in which signaling occurs. Additionally, Nonexpressor of PR 1 (NPR1), a key SA signaling protein important for regulating defenses and cell death, also acts to promote cell division and/or suppress endoreduplication during leaf development. We propose that SA interacts with multiple receptors or signaling pathways to control cellular alterations during normal development, pathogen attack and/or stress situations. We suggest that SA and NPR1 play broader roles in cell fate control than has previously been understood.
Graft transmission of induced and spontaneous post‐transcriptional silencing of chitinase genes
Authors: Crété Patrice , Leuenberger Sabrina , Iglesias Victor A. , Suarez Vivian , Schöb Hanspeter , Holtorf Hauke , Van Eeden Sjoerd , Meins Frederick 
Published: March 2003

SummarySense and antisense tobacco chitinase (CHN) transgenes, Luciferase‐CHN transcriptional fusions, and promoterless CHN cDNAs were introduced biolistically into CHN transformants of tobacco that never exhibit spontaneous gene silencing. All of the constructs tested induced systemic silencing of the resident CHN transgene and endogenes. Nuclear run‐on transcription assays showed that local introduction of additional gene copies triggers systemic post‐transcriptional gene silencing (PTGS). Together, this provides evidence that additional transgene copies need not be either highly transcribed or produce sense transcripts to evoke production of systemic PTGS signals. CHN PTGS was transmitted by top grafting, but not by reciprocal grafting of mature stems or the exchange of tissue plugs. Thus, the commonly encountered difficulties in achieving graft‐transmission could reflect the method used. Silencing in sense but not antisense transformants was transmitted by grafting to a high‐expressing sense CHN scion suggesting that the elaboration of mobile signals may not be an essential feature of antisense‐mediated gene silencing.
Involvement of the Arabidopsisα‐DOX1 fatty acid dioxygenase in protection against oxidative stress and cell death
Authors: De León Inés Ponce , Sanz Ana , Hamberg Mats , Castresana Carmen 
Published: March 2003

Summaryα‐dioxygenases (α‐DOXs) catalyze the primary oxygenation of fatty acids into a newly identified group of oxylipins. Here we show that expression of the Arabidopsis α‐DOX1 gene is induced in response to both incompatible and compatible bacterial infections. However, the level of α‐DOX1 mRNA and dioxygenase activity appears earlier and reaches higher values when infection promotes a hypersensitive reaction. Furthermore, whereas gene expression is confined to necrotic lesions during the hypersensitive response, it occurs throughout the chlorotic area during a compatible interaction. Accumulation of α‐DOX1 transcripts is impaired in SA‐compromised plants and induced by SA and by chemicals generating nitric oxide (NO), intracellular superoxide or singlet oxygen, three signals mediating host cell death. Transgenic plants with altered levels of α‐dioxygenase react like wild‐type plants to a compatible pathogen. In contrast, plants with reduced activity develop a more rapid and severe necrotic response than wild‐type plants to incompatible bacteria and paraquat treatment, respectively, and a milder response when α‐DOX1 is overproduced. Our results suggest that plant α‐dioxygenases are used to generate lipid‐derived molecules for a process that protects plant tissues from oxidative stress and cell death.
Arabidopsis glt1‐T mutant defines a role for NADH‐GOGAT in the non‐photorespiratory ammonium assimilatory pathway
Authors: Lancien Muriel , Martin Melinda , Hsieh Ming‐Hsiun , Leustek Tom , Goodman Howard , Coruzzi Gloria M. 
Published: March 2003

SummaryThe physiological role of the NADH‐dependent glutamine‐2‐oxoglutarate aminotransferase (NADH‐GOGAT) enzyme was addressed in Arabidopsis using gene expression analysis and by the characterization of a knock‐out T‐DNA insertion mutant (glt1‐T) in the single NADH‐GOGAT GLT1 gene. The NADH‐GOGAT GLT1 mRNA is expressed at higher levels in roots than in leaves. This expression pattern contrasts with GLU1, the major gene encoding Fd‐GOGAT, which is most highly expressed in leaves and is involved in photorespiration. These distinct organ‐specific expression patterns suggested a non‐redundant physiological role for the NADH‐GOGAT and Fd‐GOGAT gene products. To test the in vivo function of NADH‐GOGAT, we conducted molecular and physiological analysis of the glt1‐T mutant, which is null for NADH‐GOGAT, as judged by mRNA level and enzyme activity. Metabolic analysis showed that the glt1‐T mutant has a specific defect in growth and glutamate biosynthesis when photorespiration was repressed by 1% CO2. Under these conditions, the glt1‐T mutant displayed a 20% decrease in growth and a dramatic 70% reduction in glutamate levels. Herein, we discuss the significance of NADH‐GOGAT in non‐photorespiratory ammonium assimilation and in glutamate synthesis required for plant development.
Biochemical evidence for ubiquitin ligase activity of the Arabidopsis COP1 interacting protein 8 (CIP8)
Authors: Hardtke Christian S. , Okamoto Haruko , Stoop‐Myer Chatanika , Deng Xing Wang 
Published: March 2003

Summary Arabidopsis COP1 is a negative regulator of photomorphogenesis, which targets HY5, a positive regulator of photomorphogenesis, for degradation via the proteasome pathway in the absence of light. COP1 and its interactive partner CIP8 both possess RING finger motifs, characteristic of some E3 ubiquitin ligases. Here we show that CIP8 promotes ubiquitin attachment to HY5 in E2‐dependent fashion in vitro. CIP8 exhibits a strong interaction with the E2 enzyme AtUBC8 through its N‐terminal domain. Phosphorylation of HY5 by casein kinase II requires the beta subunit 2, but does not affect HY5′s susceptibility to ubiquitination. The RING domain of CIP8 is required but is not sufficient for ubiquitin ligase activity. Although the RING domain of CIP8 interacts with the RING domain of COP1, addition of recombinant COP1 fails to affect CIP8′s ubiquitin ligase activity towards HY5 in vitro. However, recombinant COP1 can pull‐down native CIP8 from the extract of dark‐grown seedlings, but not from the extract of light‐grown seedlings in a column‐binding assay, implying a requirement for light‐regulated modification in vivo. Our data suggest that CIP8 can form a minimal ubiquitin ligase in co‐operation with the E2 enzyme AtUBC8. It is possible that the AtUBC8‐CIP8 module might interact with COP1 in vivo, thereby participating in proteasome‐mediated degradation of HY5.
Antisense suppression of l‐galactose dehydrogenase in Arabidopsis thaliana provides evidence for its role in ascorbate synthesis and reveals light modulated l‐galactose synthesis
Authors: Gatzek Stephan , Wheeler Glen L. , Smirnoff Nicholas 
Published: March 2003

Summary l‐Galactose dehydrogenase (l‐GalDH), a novel enzyme that oxidizes l‐Gal to l‐galactono‐1,4‐lactone (l‐GalL), has been purified from pea seedlings and cloned from Arabidopsis thaliana. l‐GalL is a proposed substrate for ascorbate biosynthesis in plants, therefore the function of l‐GalDH in ascorbate biosynthesis was investigated by overexpression in tobacco and antisense suppression in A. thaliana. In tobacco the highest expressing lines had a 3.5‐fold increase in extractable activity, but this did not increase leaf ascorbate concentration. Arabidopsis thaliana, transformed with an antisense l‐GalDH construct, produced lines with 30% of wild‐type activity. These had lower leaf ascorbate concentration when grown under high light conditions. l‐Gal pool size increased in antisense transformants with low l‐GalDH activity, and l‐Gal concentration was negatively correlated with ascorbate. The results provide direct evidence for a role of l‐GalDH in ascorbate biosynthesis. Ascorbate pool size in A. thaliana is increased by acclimation to high light, but l‐GalDH expression was not affected. l‐Gal accumulation was higher in antisense plants acclimated to high light, indicating that the capacity to synthesize l‐Gal from GDP‐mannose is increased. Because the only known function of l‐GalL is ascorbate synthesis, these antisense plants provide an opportunity to investigate ascorbate function with minimal effects on carbohydrate metabolism. Measurements of other antioxidants revealed an increase in ascorbate‐ and pyrogallol‐dependent peroxidase activity in low‐ascorbate lines. As ascorbate is the major hydrogen peroxide‐scavenging antioxidant in plants, this could indicate a compensatory mechanism for controlling hydrogen peroxide concentration.