bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel auxin transport inhibitors phenocopy the auxin influx carrier mutation aux1
Authors: Parry Geraint , Delbarre Alain , Marchant Alan , Swarup Ranjan , Napier Richard , Perrot‐Rechenmann Catherine , Bennett Malcolm J. 
Published: March 2003

SummaryThe hormone auxin is transported in plants through the combined actions of diffusion and specific auxin influx and efflux carriers. In contrast to auxin efflux, for which there are well documented inhibitors, understanding the developmental roles of carrier‐mediated auxin influx has been hampered by the absence of specific competitive inhibitors. However, several molecules that inhibit auxin influx in cultured cells have been described recently. The physiological effects of two of these novel influx carrier inhibitors, 1‐naphthoxyacetic acid (1‐NOA) and 3‐chloro‐4‐hydroxyphenylacetic acid (CHPAA), have been investigated in intact seedlings and tissue segments using classical and new auxin transport bioassays. Both molecules do disrupt root gravitropism, which is a developmental process requiring rapid auxin redistribution. Furthermore, the auxin‐insensitive and agravitropic root‐growth characteristics of aux1 plants were phenocopied by 1‐NOA and CHPAA. Similarly, the agravitropic phenotype of inhibitor‐treated seedlings was rescued by the auxin 1‐naphthaleneacetic acid, but not by 2,4‐dichlorophenoxyacetic acid, again resembling the relative abilities of these two auxins to rescue the phenotype of aux1. Further investigations have shown that none of these compounds block polar auxin transport, and that CHPAA exhibits some auxin‐like activity at high concentrations. Whilst results indicate that 1‐NOA and CHPAA represent useful tools for physiological studies addressing the role of auxin influx in planta, 1‐NOA is likely to prove the more useful of the two compounds.
Quinone oxidoreductase message levels are differentially regulated in parasitic and non‐parasitic plants exposed to allelopathic quinones
Authors: Matvienko Marta , Wojtowicz Angela , Wrobel Russell , Jamison Denneal , Goldwasser Yaakov , Yoder John I. 
Published: March 2003

SummaryAllelopathic chemicals released by plants into the rhizosphere have effects on neighboring plants ranging from phytoxicity to inducing organogenesis. The allelopathic activity of naturally occurring quinones and phenols is primarily a function of reactive radicals generated during redox cycling between quinone and hydroquinone states. We isolated cDNAs encoding two distinct quinone oxidoreductases from roots of the parasitic plant Triphysaria treated with the allelopathic quinone 2,6‐dimethoxybenzoquinone (DMBQ). TvQR1 is a member of the ζ‐crystallin quinone oxidoreductase family that catalyzes one‐electron quinone reductions, generating free radical semiquinones. TvQR2 belongs to a family of detoxifying quinone oxidoreductases that catalyze bivalent redox reactions which avoid the radical intermediate. TvQR1 and TvQR2 message levels are rapidly upregulated in Triphysaria roots as a primary response to treatment with various allelopathic quinones. Inhibition of quinone oxidoreductase enzymatic activity with dicumarol prior to quinone treatment resulted in increased transcript levels. While TvQR2 homologs were upregulated by DMBQ in roots of all plants examined, TvQR1 homologs were upregulated only in roots of parasitic plants. Phylogenetic trees constructed of TvQR1 and TvQR2 protein homologs in Archea, Eubacteria and Eukaryotes indicated that both gene families are ancient, yet the families have dissimilar evolutionary histories in angiosperms. We hypothesize that TvQR2‐like proteins function to detoxify allelopathic quinones in the rhizosphere, while TvQR1 has specific functions associated with haustorium development in parasitic plants.
Evidence for the plant‐specific intercellular transport of the Arabidopsis copper chaperone CCH
Authors: Mira Helena , Martínez‐García Fernando , Peñarrubia Lola 
Published: March 2003

SummaryArabidopsis copper chaperone (CCH) belongs to a family of eukaryotic proteins that participates in intracellular copper homeostasis by delivering this metal to the secretory pathway. In this work we show that the CCH protein is mainly located along the vascular bundles of senescing leaves and petioles, as shown by tissue prints and immunohistochemical detection. CCH protein also accumulates in stem sieve elements and is collected in phloem exudates. Accordingly, Arabidopsis CCH is the only member of the metallochaperone family described to function intercellularly to date. Moreover, the CCH protein remains stable when plants are subjected to excess copper that causes a rapid and specific decrease in its mRNA. These facts point to a role for CCH in copper mobilization from decaying organs towards reproductive structures, as a result of metalloprotein breakdown.
A potato tuber‐expressed mRNA with homology to steroid dehydrogenases affects gibberellin levels and plant development
Authors: Bachem Christian W.B. , Horvath Beatrix , Trindade Luisa , Claassens Margo , Davelaar Evert , Jordi Wilco , Visser Richard G. F. 
Published: March 2003

SummaryUsing cDNA‐AFLP RNA fingerprinting throughout potato tuber development, we have isolated a transcript‐derived fragment (TDF511) with strong homology to plant steroid dehydrogenases. During in vitro tuberization, the abundance profile of the TDF shows close correlation to the process of tuber formation. However, when tuberization is inhibited by the addition of gibberellins (GAs) to the growth medium, the appearance of TDF511 in the fingerprint is delayed, then steadily increases in intensity during later stages of development. TDF511 was used to isolate the corresponding cDNA (CB12). The DNA and deduced amino‐acid sequences of the cDNA show high homology to a fruit‐ripening gene from tomato, a series of steroid dehydrogenases, and the maize Ts2 gene. A section of the cDNA was cloned in antisense orientation behind a 35S CaMV promoter and transformed into potato. Transgenic plants expressing the antisense gene showed significantly earlier emergence, an increase in height, and longer tuber shape. In vitro tuberization experiments reveal extended stolon lengths in comparison to the controls. The analysis of endogenous GA levels showed that the transgenic antisense plants have elevated levels of biologically active GAs and their respective precursors. We propose that this gene plays a role in the metabolism of plant‐growth substances important for tuber life cycle and plant development.
Collateral gene expression changes induced by distinct plant viruses during the hypersensitive resistance reaction in Chenopodium amaranticolor
Authors: Cooper Bret 
Published: March 2003

SummaryHypersensitive reactions to plant diseases are typically mediated by R genes. Many R genes that have been cloned only confer resistance to a particular pathogen. However, Chenopodium spp. have multivirus hypersensitive resistance, thus making the understanding of this broad‐spectrum resistance mechanism attractive. Using tobacco mosaic virus (TMV) tagged with green fluorescent protein to follow infection over time, cDNA‐AFLP to find genes up‐regulated during virus infection in C. amaranticolor and quantitative RT–PCR to accurately measure gene expression at different time points, the first dissection of this significant defense response pathway is presented. The detected disease‐expressed sequences in C. amaranticolor (DESCA) are similar to those that encode p450 monooxegenases, hypersensitivity‐related genes, cellulases, ABC transporters, receptor‐like kinases, serine/threonine kinases, phosphoribosylanthranilate transferases and hypothetical R genes, many of which are associated with pathogen defense in other plants. The expressions of these DESCA genes are also induced by infection with the taxonomically distinct tobacco rattle virus (TRV) in C. amaranticolor. In particular, DESCA1, one of the gene fragments from C. amaranticolor that lacks similarity to any other sequence in the GenBank database, is induced at least 200 fold 4 d after infection (dai) by both TMV and TRV. The potential role of DESCA genes in a C. amaranticolor multivirus defense response with regard to their levels and time of gene expression is discussed.
A deficiency of coproporphyrinogen III oxidase causes lesion formation in Arabidopsis
Authors: Ishikawa Atsushi , Okamoto Hiroki , Iwasaki Yukimoto , Asahi Tadashi 
Published: March 2003

SummaryWe isolated an Arabidopsis lesion initiation 2 (lin2) mutant, which develops lesion formation on leaves and siliques in a developmentally regulated and light‐dependent manner. The phenotype of the lin2 plants resulted from a single nuclear recessive mutation, and LIN2 was isolated by a T‐DNA tagging approach. LIN2 encodes coproporphyrinogen III oxidase, a key enzyme in the biosynthetic pathway of chlorophyll and heme, a tetrapyrrole pathway, in Arabidopsis. The lin2 plants express cytological and molecular markers associated with the defense responses, usually activated by pathogen infection. These results demonstrate that a porphyrin pathway impairment is responsible for the lesion initiation phenotype, which leads to the activation of defense responses, in Arabidopsis. Lesion formation was not suppressed, and was even enhanced when accumulation of salicylic acid (SA) was prevented in lin2 plants by the expression of an SA‐degrading salicylate hydroxylase (nahG) gene. This suggests that the lesion formation triggered in lin2 plants is determined prior to or independently of the accumulation of SA but that the accumulation is required to limit the spread of lesions in lin2 plants.
The mobility of the tobacco Tnt1 retrotransposon correlates with its transcriptional activation by fungal factors
Authors: Melayah Delphine , Bonnivard Eric , Chalhoub Boulos , Audeon Colette , Grandbastien Marie‐Angèle 
Published: March 2003

SummaryWe have analyzed the stress‐induced amplification of the tobacco Tnt1 element, one of the rare active plant retrotransposons. Tnt1 mobility was monitored using the retrotransposon‐anchored SSAP strategy that allows the screening of multiple insertion sites of high copy number elements. We have screened for Tnt1 insertion polymorphisms in plants regenerated from mesophyll leaf cells, either via explant culture or via protoplast isolation. The second procedure includes an overnight exposure to fungal extracts known to induce high levels of Tnt1 transcription. Newly transposed Tnt1 copies were detected in nearly 25% of the plants regenerated via protoplast isolation, and in less than 3% of the plants derived from explant culture. These results show that Tnt1 transcription is followed by transposition, and that fungal extracts efficiently activate Tnt1 mobility. Transcription appears to be the key step to controlling Tnt1 amplification, as newly transposed Tnt1 copies show high sequence similarities to the subpopulations of transcribed Tnt1 elements. Our results provide direct evidence that factors of microbial origin are able to induce retrotransposon amplification in plants, and strengthen the hypothesis that stress modulation of transposable elements might play a role in generating host genetic plasticity in response to environmental stresses.
Evidence for structurally specific negative feedback in the Nod factor signal transduction pathway
Authors: Oldroyd Giles E. D. , Mitra Raka M. , Wais Rebecca J. , Long Sharon R. 
Published: March 2003

SummaryNod factor is a critical signalling molecule in the establishment of the legume/rhizobial symbiosis. The Nod factor of Sinorhizobium meliloti carries O‐sulphate, O‐acetate and C16:2N‐acyl attachments that define its activity and host specificity. Here we assess the relative importance of these modifications for the induction of calcium spiking in Medicago truncatula. We find that Nod factor structures lacking the O‐sulphate, structures lacking the O‐acetate and N‐acyl groups, and structures lacking the O‐acetate combined with a C18:1N‐acyl group all show calcium spiking when applied at high concentrations. These calcium responses are blocked in dmi1 and dmi2 mutants, suggesting that they function through the Nod factor signal transduction pathway. The dmi3 mutant, which is proposed to function in the Nod factor signal transduction pathway downstream of calcium spiking, shows increased sensitivity to Nod factor. This increased sensitivity is only active with wild‐type Nod factor and was not present when the plants were treated with mutant Nod factor structures. We propose that the Nod factor signal transduction pathway is under negative feedback regulation that is activated at or downstream of DMI3 and requires structural components of the Nod factor molecule for activity.
In situ analysis of lignins in transgenic tobacco reveals a differential impact of individual transformations on the spatial patterns of lignin deposition at the cellular and subcellular levels
Authors: Chabannes Matthieu , Ruel Katia , Yoshinaga Arata , Chabbert Brigitte , Jauneau Alain , Joseleau Jean‐Paul , Boudet Alain‐Michel 
Published: March 2003

SummaryUsing tobacco transgenic lines altered in the monolignol biosynthetic pathway and which differ in their lignin profiles we have evaluated lignin deposition at the cellular and subcellular levels using several microanalytical techniques. Surprisingly, whereas a Cinnamoyl CoA reductase (CCR) down‐regulated line with a strong decrease in lignin content exhibited an overall reduction in lignin deposition in the walls of the different xylem cell types, this reduction was selectively targeted to the fibers in a double transformant (down‐regulated for both CCR and Cinnamyl alcohol dehydrogenase (CAD)) displaying a similar degree of global lignin content decrease. Fiber and vessel secondary walls of the transgenic tobacco line homozygous for the ccr antisense gene (CCR.H) down‐regulated plants were dramatically destructured, particularly in the S2 sublayer, whereas the deposition of lignins in the S1 sublayer was not significantly modified. In contrast, cell wall organization was slightly altered in xylem cells of the double transformant. The relative distribution of non‐condensed and condensed units in lignin, evaluated microscopically with specific antibodies, was differentially affected in the transgenics studied and, in a general way, a drop in non‐condensed lignin units (β− 0–4 interunit linkages) was associated with a loss of cohesion and extensive disorganization of the secondary wall. These results demonstrate that lignification is tightly and independently regulated in individual cell types and cell wall sublayers. They also show that down‐regulation of specific genes may induce targeted changes in lignin structure and in spatial deposition patterns of the polymer.
Two glucosyltransferases are involved in detoxification of benzoxazinoids in maize
Authors: Von Rad Uta , Hüttl Regina , Lottspeich Friedrich , Gierl Alfons , Frey Monika 
Published: March 2003

SummaryBenzoxazinoids are major compounds involved in chemical defence in grasses. These toxins are stored in the vacuole as glucosides. Two glucosyltransferases, BX8 and BX9, that catalyse this last step of benzoxazinoid biosynthesis have been isolated via functional cloning. No close relative of these maize genes was found among the known glucosyltransferases. The enzymes display a very high degree of substrate specificity. DIMBOA, the major benzoxazinoid in young maize, is the preferred substrate. Both genes are highly expressed in young maize seedlings, the developmental stage with the highest activity of benzoxazinoid biosynthesis. Bx8 is included in the cluster of DIMBOA biosynthesis genes located on the short arm of chromosome 4. Hence, the gene cluster comprises three different enzymatic functions and a complete set of genes for the biosynthesis of DIBOA glucoside. Bx9 mapped to chromosome 1. Expression of Bx8 and Bx9 in Arabidopsis corroborated the potency of the enzymes in detoxification of their substrates. This capacity might have implications for allelopathic interactions.
The participation of AtXPB1, the XPB/RAD25 homologue gene from Arabidopsis thaliana, in DNA repair and plant development
Authors: Costa Renata M. A. , Morgante Patrícia G. , Berra Carolina M. , Nakabashi Myna , Bruneau Dominique , Bouchez David , Sweder Kevin S. , Van Sluys Marie‐Anne , Menck Carlos F. M. 
Published: March 2003

SummaryNucleotide excision repair in Arabidopsis thaliana differs from other eukaryotes as it contains two paralogous copies of the corresponding XPB/RAD25 gene. In this work, the functional characterization of one copy, AtXPB1, is presented. The plant gene was able to partially complement the UV sensitivity of a yeast rad25 mutant strain, thus confirming its involvement in nucleotide excision repair. The biological role of AtXPB1 protein in A. thaliana was further ascertained by obtaining a homozygous mutant plant containing the AtXPB1 genomic sequence interrupted by a T‐DNA insertion. The 3′ end of the mutant gene is disrupted, generating the expression of a truncated mRNA molecule. Despite the normal morphology, the mutant plants presented developmental delay, lower seed viability and a loss of germination synchrony. These plants also manifested increased sensitivity to continuous exposure to the alkylating agent MMS, thus suggesting inefficient DNA damage removal. These results indicate that, although the duplication seems to be recent, the features described for the mutant plant imply some functional or timing expression divergence between the paralogous AtXPB genes. The AtXPB1 protein function in nucleotide excision repair is probably required for the removal of lesions during seed storage, germination and early plant development.
Determination of the elemental composition of mature wheat grain using a modified secondary ion mass spectrometer (SIMS)
Authors: Heard Peter J. , Feeney Kevin A. , Allen Geoffrey C. , Shewry Peter R. 
Published: March 2003

SummaryAn imaging secondary ion mass spectrometry system has been developed that allows the distribution of elements or ions to be superimposed on an image of the plant cell or tissue generated by ion‐induced secondary electrons. This system has been evaluated by analysing the aleurone and sub‐aleurone cells of mature wheat grain, showing high spatial resolution (100–200 nm) images of O–, PO2–, Mg+, Ca+, Na+ and K+ within the phytate granules of the aleurone, with CN– being diagnostic for proteins and C2– being diagnostic for starch in the starchy endosperm cells. This system should provide improved localization of elements in a range of other plant systems.
Over‐expression of TGA5, which encodes a bZIP transcription factor that interacts with NIM1/NPR1, confers SAR‐independent resistance in Arabidopsis thaliana to Peronospora parasitica
Authors: Kim Han Suk , Delaney Terrence P. 
Published: March 2003

SummaryThe Arabidopsis thaliana NIM1/NPR1 gene product is required for induction of systemic acquired resistance (SAR) by pathogens, salicylic acid (SA) or synthetic SA analogs. We identified, in a yeast two‐hybrid screen, two NIM1/NPR1 interacting proteins, TGA2 and TGA5, which belong to the basic region, leucine zipper (bZIP) family of transcription factors. Both TGA2 and TGA5 strongly interact with NIM1/NPR1 in yeast and in vitro, and recognize the as‐1 cis element found within the promoter of several pathogenesis‐related genes, such as PR‐1. To determine the role TGA2 and TGA5 may play in NIM1/NPR1‐mediated disease resistance, we introduced sense and antisense versions of both genes into transgenic Arabidopsis plants. Characterization of TGA2 transgenic plants revealed that inhibition or overexpression of TGA2 does not significantly affect PR‐1 expression or induction of SAR after pathogen infection or INA treatment. Surprisingly, all TGA5‐antisense transgenic plants produced showed increased accumulation of TGA5 transcripts compared with untransformed control plants, while the TGA5‐sense lines showed no significant increase in TGA5 mRNA levels. Interestingly, the high level of TGA5 mRNA in the antisense lines was accompanied by significant resistance to a highly virulent isolate of the oomycete pathogen Peronospora parasitica. Further, resistance was not coupled to accumulation of products from the SAR‐linked PR‐1 gene following inoculation with P. parasitica or treatment with INA, indicating that these plants express a robust, PR‐1‐independent resistance mechanism. Resistance was retained when a TGA5‐accumulating line was combined genetically with a nim1‐1 mutation or nahG (salicylate hydroxylase) transgene, indicating that resistance in these plants is due to an SA and SAR‐independent mechanism.
Impaired sucrose‐induction mutants reveal the modulation of sugar‐induced starch biosynthetic gene expression by abscisic acid signalling
Authors: Rook Fred , Corke Fiona , Card Roderick , Munz Georg , Smith Caroline , Bevan Michael W. 
Published: March 2003

SummaryPlants both produce and utilize carbohydrates and have developed mechanisms to regulate their sugar status and co‐ordinate carbohydrate partitioning. High sugar levels result in a feedback inhibition of photosynthesis and an induction of storage processes. We used a genetic approach to isolate components of the signalling pathway regulating the induction of starch biosynthesis. The regulatory sequences of the sugar inducible ADP‐glucose pyrophosphorylase subunit ApL3 were fused to a negative selection marker. Of the four impaired sucrose induction (isi) mutants described here, two (isi1 and isi2) were specific to this screen. The other two mutants (isi3 and isi4) showed additional phenotypes associated with sugar‐sensing screens that select for seedling establishment on high‐sugar media. The isi3 and isi4 mutants were found to be involved in the abscisic acid signalling pathway. isi3 is allelic to abscisic acid insensitive4 (abi4), a gene encoding an Apetala2‐type transcription factor; isi4 was found to be allelic to glucose insensitive1 (gin1) previously reported to reveal cross‐talk between ethylene and glucose signalling. Here we present an alternative interpretation of gin1 as an allele of the ABA‐deficient mutant aba2. Expression analysis showed that ABA is unable to induce ApL3 gene expression by itself, but greatly enhances ApL3 induction by sugar. Our data suggest a major role for ABA in relation to sugar‐signalling pathways, in that it enhances the ability of tissues to respond to subsequent sugar signals.
Evidence of mitochondrial involvement in the transduction of signals required for the induction of genes associated with pathogen attack and senescence
Authors: Maxwell Denis P. , Nickels Roxy , McIntosh Lee 
Published: March 2003

SummaryUsing the mRNA differential display technique, seven cDNAs have been isolated that are rapidly induced when cultured tobacco (Nicotiana tabacum) cells are treated with the mitochondrial electron transport inhibitor antimycin A (AA). Interestingly, six of the cDNAs show distinct similarity to genes known to be induced by processes that involve programmed cell death (PCD), such as senescence and pathogen attack. All of the cDNAs as well as Aox1, a gene encoding the alternative oxidase, were found to also be strongly induced by H2O2 and salicylic acid (SA). AA, H2O2 and SA treatment of tobacco cells caused a rapid rise in intracellular ROS accumulation that, when prevented by antioxidant treatment, resulted in inhibition of gene induction. Besides AA, both H2O2 and SA were found to disrupt normal mitochondrial function resulting in decreased rates of electron transport and a lowering of cellular ATP levels. Furthermore, the pre‐treatment of tobacco cells with bongkrekic acid, a known inhibitor of the mitochondrial permeability transition pore in animal cells, was found to completely block gene induction when AA, H2O2 or SA were subsequently added. These findings suggest that the mitochondrion may serve an important role in conveying intracellular stress signals to the nucleus, leading to alterations in gene expression.