bluuebunny/crossref_metadata_2025_split huggingface dataset:
Opposing roles of phytochrome A and phytochrome B in early cryptochrome‐mediated growth inhibition
Authors: Folta Kevin M. , Spalding Edgar P. 
Published: March 2003

SummaryThe cryptochrome 1 (cry1) photoreceptor is responsible for the majority of the inhibitory effect of blue light on hypocotyl elongation, but phytochrome photoreceptors also contribute to the response through a phenomenon known as coaction. In Arabidopsis thaliana the participation of phytochromes A and B (phyA and phyB) in the early phase of cry1 action was investigated by determining the effects of phyA, phyB and hy1 mutations on a cry1‐dependent membrane depolarization, which is caused by the activation of plasma‐membrane anion channels within seconds of blue light treatment. High‐resolution growth measurements were also performed to determine the timing of the requirement for phytochrome in cry1‐mediated growth inhibition, which is causally linked to the preceding anion‐channel activation. A null mutation in PHYA impaired the membrane depolarization and prevented the early cry1‐dependent phase of growth inhibition as effectively and with the same time course as mutations in CRY1. Thus, phyA is necessary for cry1/cry2 to activate anion channels within the first few seconds of blue light and to suppress hypocotyl elongation for at least 120 min. This finding furthers the notion of an intimate mechanistic association between the cry and phy receptors in mediating light responses. The absence of phyB did not affect the depolarization or growth inhibition during this time frame. Instead, double mutant analyses showed that the phyB mutation suppressed the early growth phenotypes of both phyA and cry1 seedlings. This result is consistent with the emerging view that the prevailing growth rate of a stem is a compromise between light‐dependent inhibitory and promotive influences. It appears that phyB opposes the cry1/phyA‐mediated inhibition by promoting growth during at least the first 120 min of blue light treatment.
ABA plays a central role in mediating the regulatory effects of nitrate on root branching in Arabidopsis
Authors: Signora Laurent , De Smet Ive , Foyer Christine H , Zhang Hanma 
Published: March 2003

SummaryThe formation of lateral roots (LR) is a major post‐embryonic developmental event in plants. In Arabidopsis thaliana, LR development is inhibited by high concentrations of NO3–. Here we present strong evidence that ABA plays an important role in mediating the effects of NO3– on LR formation. Firstly, the inhibitory effect of NO3– is significantly reduced in three ABA insensitive mutants, abi4‐1, abi4‐2 and abi5‐1, but not in abi1‐1, abi2‐1 and abi3‐1. Secondly, inhibition by NO3– is significantly reduced, but not completely abolished, in four ABA synthesis mutants, aba1‐1, aba2‐3, aba2‐4 and aba3‐2. These results indicate that there are two regulatory pathways mediating the inhibitory effects of NO3– in A. thaliana roots. One pathway is ABA‐dependent and involves ABI4 and ABI5, whereas the second pathway is ABA‐independent. In addition, ABA also plays a role in mediating the stimulation of LR elongation by local NO3– applications.
Analysis of surface growth in shoot apices
Authors: Dumais Jacques , Kwiatkowska Dorota 
Published: March 2003

SummaryA salient feature of shoot meristem growth is the maintenance of distinct anatomical and morphological features despite a continuous flux of cells. To investigate how meristem organization is self‐perpetuated, we developed a protocol for the analysis of meristem growth in 3‐D. Our protocol uses a non‐destructive replica method to follow the pattern of cell expansion and cell divisions on the meristem surface over several days. Algorithms to reconstruct the meristem surface and compute its curvature and rate of extension were implemented. We applied this approach to the shoot apical meristem of Anagallis arvensis and showed that a subcellular resolution of extension rates can be achieved. This is the first detailed quantitative analysis of meristem geometry and surface expansion in 3‐D. This new approach will be useful to connect cellular activities such as cell expansion, cell division, and differential gene expression with overall meristem morphogenesis.
HFR1, a phytochrome A‐signalling component, acts in a separate pathway from HY5, downstream of COP1 in Arabidopsis thaliana
Authors: Kim Young‐Mi , Woo Je‐Chang , Song Pill‐Soon , Soh Moon‐Soo 
Published: March 2003

SummaryHFR1, a basic helix–loop–helix protein, is known to be required for a subset of phytochrome A (phyA)‐dependent photoresponses. To investigate the role of HFR1 in light signalling, we have examined the genetic interaction between HFR1 and HY5, a positive regulator of light signalling, and COP1, a repressor of photomorphogenesis. Double mutant analysis suggests that HFR1 mediates phyA‐dependent inhibition of hypocotyl elongation independently of HY5. HFR1 was shown to be necessary for a subset of cop1‐triggered photomorphogenic phenotypes in the dark, including inhibition of hypocotyl elongation, gravitropic hypocotyl growth, and expression of the light‐inducible genes CAB and RBCS. Phenotypic analysis of the triple mutant cop1hy5hfr1 indicated that both HFR1 and HY5 are required for cop1‐mediated photomorphogenic seedling development in darkness, consistent with their additive roles in phyA‐dependent signalling. Taken together, these results suggest that HFR1 might act downstream of COP1, in a separate pathway from HY5, to mediate photomorphogenesis in Arabidopsis.
Post‐transcriptional mechanisms control catalase synthesis during its light‐induced turnover in rye leaves through the availability of the hemin cofactor and reversible changes of the translation efficiency of mRNA
Authors: Schmidt Matthias , Dehne Silvia , Feierabend Jürgen 
Published: March 2003

SummaryThe enzyme catalase is light‐sensitive. In leaves, losses caused by photoinactivation are replaced by new enzyme and the rate of de novo synthesis must be rapidly and flexibly attuned to fluctuating light conditions. In mature rye leaves, post‐transcriptional mechanisms were shown to control the rate of catalase synthesis. The amount of the leaf catalase (CAT‐1) transcript did not increase with light intensity, but was even higher after dark exposure of light‐grown leaves. Initiation was apparently not limiting translation in the dark, as the association of the Cat1 mRNA with polysomes did not change notably under different light conditions. By analysing the translation of catalase polypeptides in cell‐free systems with poly(A)+ RNA from leaves or with mRNA transcribed from a Cat1‐containing cDNA clone, two mechanisms of post‐transcriptional control were identified. First, translation of catalase depended on the presence of hemin. In leaves, the availability of hemin may signal the extent of catalase degradation as the hemin of the inactivated enzyme is recycled. Second, the translation efficiency of the Cat1 transcripts was reversibly modulated in a dose‐dependent manner by the light intensity to which leaves were exposed, prior to extraction. The Cat1 mRNA from light‐exposed leaves was translated much more efficiently than mRNA from dark‐exposed leaves. The increase of its translation activity in vivo was not blocked by cordycepin but was suppressed by methylation inhibitors, indicating a reversible modification of pre‐existing mRNA by methylation. Translation of in vitro synthesized Cat1 mRNA required a methylated cap (m7GpppG), but was virtually below detection when it contained an unmethylated cap (GpppG).
Isolation, cloning and expression of a multifunctional O‐methyltransferase capable of forming 2,5‐dimethyl‐4‐methoxy‐3(2H)‐furanone, one of the key aroma compounds in strawberry fruits
Authors: Wein Martina , Lavid Noa , Lunkenbein Stefan , Lewinsohn Efraim , Schwab Wilfried , Kaldenhoff Ralf 
Published: March 2003

SummaryStrawberry fruits contain an uncommon group of key aroma compounds with a 2,5‐dimethyl‐3(2H)‐furanone structure. Here, we report on the methylation of 2,5‐dimethyl‐4‐hydroxy‐3(2H)‐furanone (DMHF) to 2,5‐dimethyl‐4‐methoxy‐3(2H)‐furanone (DMMF) by a S‐adenosyl‐L‐methionine dependent O‐methyltransferase, the cloning of the corresponding cDNA and characterization of the encoded protein. Northern‐hybridization indicated that the Strawberry‐OMT specific transcripts accumulated during ripening in strawberry fruits and were absent in root, petiole, leaf and flower. The protein was functionally expressed in E. coli and exhibited a substrate specificity for catechol, caffeic acid, protocatechuic aldehyde, caffeoyl CoA and DMHF. A common structural feature of the accepted substrates was a o‐diphenolic structure also present in DMHF in its dienolic tautomer. FaOMT is active as a homodimer and the native enzyme shows optimum activity at pH 8.5 and 37°C. It does not require a cofactor for enzymatic activity. Due to the expression pattern of FaOMT and the enzymatic activity in the different stages of fruit ripening we suppose that FaOMT is involved in lignification of the achenes and the vascular bundles in the expanding fruit. In addition, it is concluded that the Strawberry‐OMT plays an important role in the biosynthesis of strawberry volatiles such as vanillin and DMMF.
Functional analysis of plastid DNA replication origins in tobacco by targeted inactivation
Authors: K. Mühlbauer Stefan , Lössl Andreas , Tzekova Lilia , Zou Zhurong ,   Hans‐Ulrich Koop
Published: March 2003

SummarySequences described as chloroplast DNA replication origins were analysed in vivo by creating deletion and insertion mutants via plastid transformation in tobacco. Deletion of the described oriA sequence, which is located within the intron of the trnI gene, resulted in heteroplastomic transformants, when the selection marker was inserted within the intron. Removal of the complete intron sequence together with the oriA sequence, however, yielded homoplastomic transformants of normal phenotype, in which wild‐type signals were no longer detectable through Southern analysis, thus bringing the role of the described oriA sequence for plastome replication into question. Similarly, deletion of sequence elements upstream of trnI, which have a possible ori function in Oenothera, did not show any effect in tobacco. The two copies of oriB, which are located at the very end of the plastome Inverted Repeats, were targeted with two different transformation vectors in a cotransformation approach. While in initial transformants integration of the selection marker could be detected at both sites, the transgene was found exclusively at one site or the other after additional rounds of regeneration. Whereas the copy of oriB in Inverted Repeat B could be completely deleted, targeting of the copy in Inverted Repeat A resulted in heteroplastomic lines, as the essential ycf1 gene was also affected. Due to the strong selection against cotransformants we conclude that at least one copy of the oriB sequence is essential for plastome replication, whereas replication appears possible without oriA elements.
Expression of a Phytophthora sojae necrosis‐inducing protein occurs during transition from biotrophy to necrotrophy
Authors: Qutob Dinah , Kamoun Sophien , Gijzen Mark 
Published: March 2003

Summary Phytophthora sojae is an oomycete that causes stem and root rot on soybean plants. To discover pathogen factors that produce disease symptoms or activate plant defense responses, we identified putative secretory proteins from expressed sequence tags (ESTs) and tested selected candidates using a heterologous expression assay. From an analysis of 3035 ESTs originating from mycelium, zoospore, and infected soybean tissues, we identified 176 putative secreted proteins. A total of 16 different cDNAs predicted to encode secreted proteins ranging in size from 6 to 26 kDa were selected for expression analysis in Nicotiana benthamiana using an Agrobacterium tumefaciens binary potato virus X (PVX) vector. This resulted in the identification of a 25.6‐kDa necrosis‐inducing protein that is similar in sequence to other proteins from eukaryotic and prokaryotic species. The genomic region encoding the P. sojae necrosis‐inducing protein was isolated and the expression pattern of the corresponding gene determined by RNA blot hybridization and by RT‐PCR. The activity of this P. sojae protein was compared to proteins of similar sequence from Fusarium oxysporum, Bacillus halodurans, and Streptomyces coelicolor by PVX‐based expression in N. benthamiana and by transient expression via particle bombardment in soybean tissues. The P. sojae protein was a powerful inducer of necrosis and cell death in both assays, whereas related proteins from other species varied in their activity. This study suggests that the P. sojae necrosis‐inducing protein facilitates the colonization of host tissues during the necrotrophic phase of growth.
Polyribosome loading of spinach mRNAs for photosystem I subunits is controlled by photosynthetic electron transport
Authors: Sherameti Irena , Nakamura Masayaki , Yamamoto Yoshiharu Y. , Pfannschmidt Thomas , Obokata Junichi , Oelmüller Ralf 
Published: March 2003

SummaryIn light‐, but not in dark‐grown spinach seedlings, the mRNAs for the nuclear‐encoded photosystem I subunits D, F and L are associated with polyribosomes and this association is prevented by the application of 3‐(3′,4′‐dichlorophenyl)‐1,1′‐dimethyl urea (DCMU), an inhibitor of the photosynthetic electron transport. To identify the cis‐elements which are responsible for this regulation, we generated a series of chimeric PsaD constructs and tested them in transgenic tobacco. The spinach PsaD 5′‐untranslated region is sufficient to confer light‐ and photosynthesis‐dependent polyribosome association onto the uidA reporter gene, while the tobacco PsaD 5′‐untranslated region directs constitutive polyribosome association. These results are discussed with regard to signals from photosynthetic electron flow which control processes in the cytoplasm.
Differential regulation of TGA transcription factors by post‐transcriptional control
Authors: Pontier Dominique , Privat Isabelle , Trifa Youssef , Zhou Jun‐Ma , Klessig Daniel F. , Lam Eric 
Published: March 2003

SummaryTranscription factors often belong to multigene families and their individual contribution in a particular regulatory network remains difficult to assess. We show here that specific members from a family of conserved Arabidopsis bZIP transcription factors, the TGA proteins, are regulated in their protein stability by developmental stage‐specific proteolysis. Using GFP fusions of three different Arabidopsis TGA factors that represent members of distinct subclasses of the TGA factor family, we demonstrate that two of these TGA proteins are specifically targeted for proteolysis in mature leaf cells. Using a supershift gel mobility assay, we found evidence for similar regulation of the cognate proteins as compared to the GFP fusion proteins expressed under the cauliflower mosaic virus (CaMV) 35S promoter. Using various inhibitors, we showed that the expression of at least one of these three TGA factors could be stabilized by inhibition of proteasome‐mediated proteolysis. This study indicates that TGA transcription factors may be regulated by distinct pathways of targeted proteolysis that can serve to modulate the contribution of specific members of a multigene family in complex regulatory pathways.
Antisense repression of StubGAL83 affects root and tuber development in potato
Authors: Lovas Ágnes , Bimbó Andrea , Szabó László , Bánfalvi Zsófia 
Published: March 2003

Summary StubGAL83 is a potato gene that encodes the β‐subunit of a protein kinase complex similar to the yeast SNF1, and the mammalian AMPK complexes that are modulated by changes in the cellular AMP/ATP ratio and are important regulators of metabolic and stress responses. Here we show that the expression of StubGAL83 in potato foliage is much higher in the dark than in the light and can be repressed by metabolisable sugars in the dark. The amounts of StubGAL83 mRNA are higher in sink than in source leaves. To unravel the role of StubGAL83, transgenic potato plants expressing a part of the StubGAL83 cDNA in antisense orientation under the control of the constitutive CaMV35S promoter were generated. Northern analysis revealed a reduction up to 90–95% in StubGAL83 mRNA accumulation in leaves of seven lines. Five out of these seven lines exhibited a reduction of StubGAL83 mRNA levels also in root and tuber tissues. Independent on the type of repression, the transgenic lines showed a delay in rooting and an increased sensitivity to salt stress. The roots were stunted and possessed less pronounced tap roots than the controls albeit with different severity in the different transgenic lines. The root cells were smaller and some of them had irregular shape. Tuberisation of the antisense‐StubGAL83 lines was delayed, the size of the tubers was reduced while the number of tubers per plant was increased. These results together suggest that StubGAL83 affects root and tuber development probably by altering the metabolic status of the leaves.
Reduced amino acid content in transgenic potato tubers due to antisense inhibition of the leaf H+/amino acid symporter StAAP1
Authors: Koch Wolfgang , Kwart Marion , Laubner Marion , Heineke Dieter , Stransky Harald , Frommer Wolf B. , Tegeder Mechthild 
Published: March 2003

SummaryTransport processes across the plasma membrane of leaf vascular tissue are essential for transport and distribution of assimilates. In potato, leaves are the predominant sites for nitrate reduction and amino acid biosynthesis. From there, assimilated amino acids are exported through the phloem to supply tubers with organic nitrogen. To study the role of amino acid transporters in long‐distance transport and allocation of organic nitrogen in potato plants, a gene encoding a functional, leaf‐expressed amino acid permeaseStAAP1was isolated. Similar to the sucrose transporter SUT1,StAAP1expression was induced during the sink‐to‐source transition, indicating a role in phloem loading. To test the role of StAAP1, expression was inhibited by an antisense approach. Transgenic plants with reducedStAAP1expression were phenotypically indistinguishable from wild type, as were photosynthetic capacity and tuber yield. However, tubers from antisenseStAAP1plants showed up to 50% reduction in free amino acid contents. In comparison, starch content was not affected or tended to increase relative to wild type. The reduction in all amino acids except aspartate in the antisense plants is consistent with the properties of amino acid permeases (AAPs) found in heterologous systems. The results demonstrate an important role forStAAP1in long‐distance transport of amino acids and highlight the importance of plasma membrane transport for nutrient distribution in plants.
The tomato mutant spr1 is defective in systemin perception and the production of a systemic wound signal for defense gene expression
Authors: Lee Gyu In , Howe Gregg A. 
Published: March 2003

SummaryWound‐induced systemic expression of defensive proteinase inhibitor (PI) genes in tomato plants requires the action of systemin and its precursor protein prosystemin. Although it is well established that systemin induces PI expression through the octadecanoid pathway for jasmonic acid (JA) biosynthesis, relatively little is known about how systemin and JA interact to promote long‐distance signaling between damaged and undamaged leaves. Here, this question was addressed by characterizing a systemin‐insensitive mutant (spr1) that was previously identified as a suppressor of prosystemin‐mediated responses. In contrast to JA biosynthetic or JA signaling mutants that lack both local and systemic PI expression in response to wounding, spr1 plants were deficient mainly in the systemic response. Consistent with this phenotype, spr1 plants exhibited normal PI induction in response to oligosaccharide signals that are thought to play a role in the local wound response. Moreover, spr1 abolished JA accumulation in response to exogenous systemin, and reduced JA accumulation in wounded leaves to approximately 57% of wild‐type (WT) levels. Analysis of reciprocal grafts between spr1 and WT plants showed that spr1 impedes systemic PI expression by blocking the production of the long‐distance wound signal in damaged leaves, rather than inhibiting the recognition of that signal in systemic undamaged leaves. These experiments suggest that Spr1 is involved in a signaling step that couples systemin perception to activation of the octadecanoid pathway, and that systemin acts at or near the site of wounding (i.e. in rootstock tissues) to increase JA synthesis to a level that is required for the systemic response. It was also demonstrated that spr1 plants are not affected in the local or systemic expression of a subset of rapidly induced wound‐response genes, indicating the existence of a systemin‐independent pathway for wound signaling.
An abscisic acid‐sensitive checkpoint in lateral root development of Arabidopsis
Authors: De Smet Ive , Signora Laurent , Beeckman Tom , Inzé Dirk , Foyer Christine H. , Zhang Hanma 
Published: March 2003

SummaryLateral root (LR) formation displays considerable plasticity in response to developmental and environmental signals. The mechanism whereby plants incorporate diverse regulatory signals into the developmental programme of LRs remains to be elucidated. Current concepts of lateral root regulation focus on the role of auxin. In this study, we show that another plant hormone, abscisic acid (ABA), also plays a critical role in the regulation of this post‐embryonic developmental event. In the presence of exogenous ABA, LR development is inhibited. This occurs at a specific developmental stage, i.e. immediately after the emergence of the LR primordium (LRP) from the parent root and prior to the activation of the LR meristem, and is reversible. Interestingly, this inhibition requires 10‐fold less ABA than the inhibition of seed germination and is only slightly reduced in characterised abi mutants, suggesting that it may involve novel ABA signalling mechanisms. We also present several lines of evidence to support the conclusion that the ABA‐induced lateral root inhibition is mediated by an auxin‐independent pathway. First, the inhibition could not be rescued by either exogenous auxin application or elevated auxin synthesis. Secondly, a mutation in the ALF3 gene, which is believed to encode an important component in the auxin‐dependent regulatory pathway for the post‐emergence LR development, does not affect the sensitivity of LRs to ABA. Thirdly, ABA and the alf3‐1 mutation do not act at the same developmental point. To summarise, these results demonstrate a novel ABA‐sensitive, auxin‐independent checkpoint for lateral root development in Arabidopsis at the post‐emergence stage. In addition, we also present data indicating that regulation of this developmental checkpoint may require novel ABA signalling mechanisms and that ABA suppresses auxin response in the LRPs.