bluuebunny/crossref_metadata_2025_split huggingface dataset:
Local and systemic wound‐induction of RNase and nuclease activities in Arabidopsis: RNS1 as a marker for a JA‐independent systemic signaling pathway
Authors: LeBrasseur Nicole D. , MacIntosh Gustavo C. , Pérez‐Amador Miguel A. , Saitoh Maki , Green Pamela J. 
Published: March 2003

SummaryInduction of defense‐related genes is one way in which plants respond to mechanical injury. We investigated whether RNases are involved in the wound response in Arabidopsis thaliana. As in other plant systems, several activities are induced with various timings in damaged leaves, stems and seedlings in Arabidopsis, including at least three bifunctional nucleases, capable of degrading both RNA and DNA, as well as RNS1, a member of the ubiquitous RNase T2 family of RNases. The strong induction of RNS1 is particularly interesting because it occurs both locally and systemically following wounding. The systemic induction of this RNase indicates that members of this family may be involved in defense mechanisms in addition to their previously hypothesized functions in nutrient recycling and remobilization. Additionally, the systemic induction appears to be controlled independently of jasmonic acid, and the local induction of RNS1 and the nuclease activities are independent of both JA and oligosaccharide elicitors. Consequently, a novel systemic pathway, likely involving a third signal, appears to exist in Arabidopsis.
Condensin and cohesin knockouts in Arabidopsis exhibit a titan seed phenotype
Authors: Liu Chun‐ming , McElver John , Tzafrir Iris , Joosen Ronny , Wittich Peter , Patton David , Van Lammeren Andre A. M. , Meinke David 
Published: March 2003

SummaryThe titan (ttn) mutants of Arabidopsis exhibit striking alterations in chromosome dynamics and cell division during seed development. Endosperm defects include aberrant mitoses and giant polyploid nuclei. Mutant embryos differ in cell size, morphology and viability, depending on the locus involved. Here we demonstrate that three TTN genes encode chromosome scaffold proteins of the condensin (SMC2) and cohesin (SMC1 and SMC3) classes. These proteins have been studied extensively in yeast and animal systems, where they modulate chromosome condensation, chromatid separation, and dosage compensation. Arabidopsis contains single copies of SMC1 and SMC3 cohesins. We used forward genetics to identify duplicate T‐DNA insertions in each gene. These mutants (ttn7 and ttn8) have similar titan phenotypes: giant endosperm nuclei and arrested embryos with a few small cells. A single SMC2 knockout (ttn3) was identified and confirmed by molecular complementation. The weak embryo phenotype observed in this mutant may result from expression of a related gene (AtSMC2) with overlapping functions. Further analysis of titan mutants and the SMC gene family in Arabidopsis should provide clues to chromosome mechanics in plants and insights into the regulation of nuclear activity during endosperm development.
Insights into the evolution of self‐compatibility in Lycopersicon from a study of stylar factors
Authors: Kondo Katsuhiko , Yamamoto Mayu , Itahashi Ryoko , Sato Takanori , Egashira Hiroaki , Hattori Tsukaho , Kowyama Yasuo 
Published: March 2003

SummaryTo elucidate the molecular basis of loss of self‐incompatibility in Lycopersicon, S‐RNases and HT‐proteins were analysed in seven self‐compatible (SC) and three self‐incompatible (SI) taxa. No or low stylar RNase activity was a common feature in most SC taxa examined, in contrast to the uniformly high levels of activity found in all SI species. The S‐RNase gene is most likely deleted in the four red‐fruited SC taxa (L. esculentum, L. esculentum var. cerasiforme, L. pimpinellifolium and L. cheesmanii) because S‐RNase genes could not be amplified from genomic DNA. S‐RNase genes could, however, be amplified from the genomes of the three green‐fruited SC taxa examined. L. chmielewskii and L. hirsutum f. glabratum show a decreased accumulation of transcripts, possibly reflecting changes in the 5′ flanking regions of the S‐RNase genes. The remaining green‐fruited SC species, L. parviflorum, has a functional S‐RNase gene in its genome that is expressed at high levels in the style, suggesting a genetic factor responsible for the low S‐RNase activity. Together these results argue for several independent mutations in the S‐RNase gene over the course of Lycopersicon diversification, and that loss of S‐RNase function is unlikely to the primary cause of the loss of self‐incompatibility. We also examined the HT‐B genes that play a role in self‐incompatibility. HT‐B transcripts were markedly reduced in the styles of all the SC taxa examined. A scenario is described where a mutation causing reduced transcription of HT‐B in an ancestral SI species was central to the loss of self‐incompatibility in Lycopersicon.
Evidence for the presence and activity of a complete antioxidant defence system in mature sieve tubes
Authors: Walz Christina , Juenger Melanie , Schad Martina , Kehr Julia 
Published: March 2003

SummaryThe phloem is the major route for the transport of solutes and nutrients from source to sink organs in plants. The functional transport phloem consists of parenchymal tissue, enucleate sieve elements, and the intimately connected companion cells. The general absence of a nucleus and functional ribosomes in sieve tubes poses problems especially for damage avoidance and repair of sieve element components. To examine how sieve tubes can remain functional during oxidative stress, we analysed phloem sap of cucumber and pumpkin plants with respect to the presence of antioxidant defence enzymes, their enzymatic activity, and activity changes after exposure to drought stress. Using 1D SDS‐PAGE and nano ESI MS/MS, the presence of proteins such as cytosolic Cu/Zn superoxide dismutase, monodehydroascorbate reductase, and peroxidase could be shown. Moreover, activities for several antioxidant enzymes (superoxide dismutase, dehydroascorbate reductase, peroxidase) in phloem exudate could be demonstrated. The activity of these enzymes in phloem sap from cucumber and pumpkin plants increased in response to drought stress. The presented results together with earlier findings provide evidence supporting the presence of a complete machinery of antioxidant defence enzymes and detoxifying metabolites important for avoiding damage to essential components of the sieve elements due to oxidative stress.
Comparative analysis of plastid transcription profiles of entire plastid chromosomes from tobacco attributed to wild‐type and PEP‐deficient transcription machineries
Authors: Legen Julia , Kemp Sabine , Krause Kirsten , Profanter Birgit , Herrmann Reinhold G. , Maier Rainer M. 
Published: March 2003

SummaryTranscription of plastid chromosomes in vascular plants is accomplished by at least two RNA polymerases of different phylogenetic origin: the ancestral (endosymbiotic) cyanobacterial‐type RNA polymerase (PEP), of which the core is encoded in the organelle chromosome, and an additional phage‐type RNA polymerase (NEP) of nuclear origin. Disruption of PEP genes in tobacco leads to off‐white phenotypes. A macroarray‐based approach of transcription rates and of transcript patterns of the entire plastid chromosome from leaves of wild‐type as well as from transplastomic tobacco lacking PEP shows that the plastid chromosome is completely transcribed in both wild‐type and PEP‐deficient plastids, though into polymerase‐specific profiles. Different probe types, run‐on transcripts, 5′ or 3′ labelled RNAs, as well as cDNAs, have been used to evaluate the array approach. The findings combined with Northern and Western analyses of a selected number of loci demonstrate further that frequently no correlation exists between transcription rates, transcript levels, transcript patterns, and amounts of corresponding polypeptides. Run‐on transcription as well as stationary RNA concentrations may increase, decrease or remain similar between the two experimental materials, independent of the nature of the encoded gene product or of the multisubunit assembly (thylakoid membrane or ribosome). Our findings show (i) that the absence of photosynthesis‐related, plastome‐encoded polypeptides in PEP‐deficient plants is not directly caused by a lack of transcription by PEP, and demonstrate (ii) that the functional integration of PEP and NEP into the genetic system of the plant cell during evolution is substantially more complex than presently supposed.
The topological specificity factor AtMinE1 is essential for correct plastid division site placement in Arabidopsis
Authors: Maple Jodi , Chua Nam‐Hai , Møller Simon G. 
Published: March 2003

SummaryIn plant cells, plastids divide by binary fission involving a complex pathway of events. Although there are clear similarities between bacterial and plastid division, limited information exists regarding the mechanism of plastid division in higher plants. Here we demonstrate that AtMinE1, an Arabidopsis homologue of the bacterial MinE topological specificity factor, is an essential integral component of the plastid division machinery. In prokaryotes MinE imparts topological specificity during cell division by blocking division apparatus assembly at sites other than midcell. We demonstrate that overexpression of AtMinE1 in E. coli results in loss of topological specificity and minicell formation suggesting evolutionary conservation of MinE mode of action. We further show that AtMinE1 can indeed act as a topological specificity factor during plastid division revealing that AtMinE1 overexpression in Arabidopsis seedlings results in division site misplacement giving rise to multiple constrictions along the length of plastids. In agreement with cell division studies in bacteria, AtMinE1 and AtMinD1 show distinct intraplastidic localisation patterns suggestive of dynamic localisation behaviour. Taken together our findings demonstrate that AtMinE1 is an evolutionary conserved topological specificity factor, most probably acting in concert with AtMinD1, required for correct plastid division in Arabidopsis.
Sequence elements within an HSP70 promoter counteract transcriptional transgene silencing in Chlamydomonas
Authors: Schroda Michael , Beck Christoph F. , Vallon Olivier 
Published: March 2003

SummaryWe have shown previously that the HSP70A (A) promoter, when fused upstream of other promoters, significantly improves their performance in driving transgene expression in Chlamydomonas. Here, we employed the bacterial resistance gene ble, driven by the RBCS2 (R) promoter or an AR promoter fusion, to determine, by which mechanism(s) the A promoter may exert its enhancing effect. We observed that transformation rates of AR‐ble constructs were significantly higher than those of R‐ble constructs. However, ble mRNA levels in pools of transformants generated with either construct type were the same. Co‐transformation experiments revealed that the R‐ble transgene was silenced in 80% of the transformants, whereas this fraction was reduced to 36% in transformants harbouring the AR‐ble transgene. We conclude that the A promoter acts by decreasing the probability that a transgene becomes transcriptionally silenced. We mapped two elements within the A promoter that are responsible for this effect. The core of the first element appears to be located between nucleotides − 7 and + 67 relative to the HSP70A transcriptional start site. Its activity is strongly dependent on its spatial setting with respect to the R promoter and is increased by upstream sequences (− 196 to − 8). The second element is independent of the first and is located to the region from − 754 to − 197. Its activity is spacing‐independent and additive to the first element.
Genotype‐dependent transcriptional activation of novel repetitive elements during cold acclimation of alfalfa (Medicago sativa)
Authors: Ivashuta Sergey , Naumkina Marina , Gau Mitsuru , Uchiyama Kazuhiro , Isobe Sachiko , Mizukami Yuko , Shimamoto Yoshiya 
Published: March 2003

SummaryIn a search for cold‐regulated genes that are differentially expressed in alfalfa genotypes of contrasting freezing tolerance, we screened 1036 arrayed cDNA clones. The screening resulted in isolation of cDNA clones, which demonstrated dramatic differences in expression between hardy and un‐hardy alfalfa varieties. Detailed analysis revealed that these cDNAs represent parts of novel non‐coding repetitive elements carrying long‐terminal repeats (LTR) and other retroelement‐like features. Despite strong expression under low temperatures, DNA templates remained highly methylated, and a drug‐induced decrease in methylation did not activate transcription under normal temperatures. We identified that these repetitive elements represent a large family and could insert into, or be adjacent to, the unrelated polyprotein sequences of putative retrotransposons. These retrotransposons also showed low temperature‐induced transcriptional activation; however, this activation was not genotype‐dependent. The retroelements described in this study are the first retroelement characterized in the Medicago genus. Furthermore, they represent the only known example of genotype‐specific cold‐induced transcriptional activation of multiple copies of a repetitive element whose expression is associated with a genotype difference in cold acclimation.
Arabidopsis onset of leaf death mutants identify a regulatory pathway controlling leaf senescence
Authors: Jing Hai‐Chun , Sturre Marcel J. G. , Hille Jacques , Dijkwel Paul P. 
Published: March 2003

SummaryThe onset of leaf senescence is controlled by leaf age and ethylene can promote leaf senescence within a specific age window. We exploited the interaction between leaf age and ethylene and isolated mutants with altered leaf senescence that are named as onset ofleafdeath (old) mutants. Early leaf senescence mutants representing three genetic loci were selected and their senescence syndromes were characterised using phenotypical, physiological and molecular markers. old1 is represented by three recessive alleles and displayed earlier senescence both in air and upon ethylene exposure. The etiolated old1 seedlings exhibited a hypersensitive triple response. old2 is a dominant trait and the mutant plants were indistinguishable from the wild‐type when grown in air but showed an earlier senescence syndrome upon ethylene treatment. old3 is a semi‐dominant trait and its earlier onset of senescence is independent of ethylene treatment. Analyses of the chlorophyll degradation, ion leakage and SAG expression showed that leaf senescence was advanced in ethylene‐treated old2 plants and in both air‐grown and ethylene‐treated old1 and old3 plants. Epistatic analysis indicated that OLD1 might act downstream of OLD2 and upstream of OLD3 and mediate the interaction between leaf age and ethylene. A genetic model was proposed that links the three OLD genes and ethylene into a regulatory pathway controlling the onset of leaf senescence.
Paternal mRNA and protein synthesis coincides with male chromatin decondensation in maize zygotes
Authors: Scholten Stefan , Lörz Horst , Kranz Erhard 
Published: March 2003

SummaryDecondensation of the male genome after fertilization is a prerequisite for replication and transcription. Cytological analysis has revealed decondensation of the male chromatin to commence immediately after karyogamy and progress rapidly, pointing to an early start of transcription. To investigate early transcription from the paternal genome in maize zygotes, we generated transgenic plants containing green fluorescent protein (GFP) under control of the 35S promoter. Single transgenic sperm cells from these plants were used to fertilize isolated wild‐type egg cells in vitro. These sperm cells did not contain gfp transcripts. Appearance of gfp mRNA, 4 h after fertilization, was coincident with decondensation of the male chromatin, and clearly demonstrates early accessibility to the transcriptional machinery of at least a part of the male genome. Translational activity in early zygotes was evident 6 h after fertilization, as demonstrated by measurable levels of GFP fluorescence signal. Using a similar strategy, we also demonstrated activity of the paternal genome early in endosperm development. These findings may exclude any global mechanism of silencing the entire paternal genome over this period, and make an almost immediate paternal contribution to zygote and early endosperm development conceivable. These data are also considered in the perspective of current views of genome activation in the zygotes and young embryos of animals.
Characterization of Arabidopsis thaliana AtFKBP42 that is membrane‐bound and interacts with Hsp90
Authors: Kamphausen Thilo , Fanghänel Jörg , Neumann Dieter , Schulz Burkhard , Rahfeld Jens‐U. 
Published: March 2003

SummaryThe twisted dwarf1 (twd1) mutant from Arabidopsis thaliana was identified in a screen for plant architecture mutants. The TWD1 gene encodes a 42 kDa FK506‐binding protein (AtFKBP42) that possesses similarity to multidomain PPIases such as mammalian FKBP51 and FKBP52, which are known to be components of mammalian steroid hormone receptor complexes. We report here for the first time the stoichiometry and dissociation constant of a protein complex from Arabidopsis that consists of AtHsp90 and AtFKBP42. Recombinant AtFKBP42 prevents aggregation of citrate synthase in almost equimolar concentrations, and can be cross‐linked to calmodulin. In comparison to one active and one inactive FKBP domain in FKBP52, AtFKBP42 lacks the PPIase active FKBP domain. While FKBP52 is found in the cytosol and translocates to the nucleus, AtFKBP42 was predicted to be membrane‐localized, as shown by electron microscopy.
Construction of a specialized cDNA library from plant cells isolated by laser capture microdissection: toward comprehensive analysis of the genes expressed in the rice phloem
Authors: Asano Takayuki , Masumura Takehiro , Kusano Hiroaki , Kikuchi Shoshi , Kurita Akihiro , Shimada Hiroaki , Kadowaki Koh‐ichi 
Published: March 2003

SummaryLaser capture microdissection (LCM) is a powerful system which allows the isolation of selectively targeted cells from a tissue section for the analysis of gene‐expression profiles of individual cells. The technique has been successfully used for the isolation of specific mammalian cells, mainly cancer cells. However, LCM has never been reported to be applied to the gene expression analysis of plant cells. We used a modified LCM system and successfully applied it to target and isolate phloem cells of rice leaf tissue whose morphology is apparently different from the surrounding cells. Total RNA was extracted from microdissected (approximately 150) phloem cells and the isolated RNA was used for the construction of a cDNA library following the T7 RNA polymerase amplification. Sequence analysis of 413 randomly chosen clones from the library revealed that there was a high level of redundancy in the population and the clones could be subclassified into 124 different groups that contained related sequences. Approximately 37% of both the redundant population and the non‐redundant subgroups had novel components while approximately 63% were either homologues to the known genes reported to be localized in phloem of different plant species, or were homologues to other known genes. In situ hybridization revealed that putative amino acid permease, one of the non‐redundant clones, was specifically expressed in the phloem. The results proved the effectiveness of construction of a specialized cDNA library from the specific plant cells.
Molecular analysis of herbivore‐induced condensed tannin synthesis: cloning and expression of dihydroflavonol reductase from trembling aspen (Populus tremuloides)
Authors: Peters Darren J. , Constabel C. Peter 
Published: March 2003

SummaryIn order to study condensed tannin synthesis and its induction by herbivory, a dihydroflavonol reductase (DFR) cDNA was isolated from trembling aspen (Populus tremuloides). Bacterial overexpression demonstrated that this cDNA encodes a functional DFR enzyme, and Southern analysis revealed that DFR likely is a single‐copy gene in the aspen genome. Aspen plants that were mechanically wounded showed a dramatic increase in DFR expression after 24 h in both wounded leaves and unwounded leaves on wounded trees. Feeding by forest tent caterpillar (Malacosoma disstria) and satin moth (Leucoma salicis) larvae, and treatment with methyl jasmonate, all strongly induced DFR expression. DFR enzyme activity was also induced in wounded aspen leaves, and phytochemical assays revealed that condensed tannin concentrations significantly increased in wounded and systemic leaves. The expression of other genes involved in the phenylpropanoid pathway were also induced by wounding. Our findings suggest that the induction of condensed tannins, compounds known to be important for defense against herbivores, is mediated by increased expression of DFR and other phenylpropanoid genes.
T‐DNA recombination and replication in maize cells
Authors: Zhao Xiaoxia , Coats Isabelle , Fu Ping , Gordon‐Kamm Bill , Lyznik L. Alexander 
Published: March 2003

SummaryT‐DNA recombination and replication was analyzed in ‘black mexican sweet’ (BMS) cells transformed with T‐DNAs containing the replication system from wheat dwarf virus (WDV). Upon recombination between the T‐DNA ends, a promoterless marker gene (gusA) was activated. Activation of the recombination marker gene was delayed and increased exponentially over time, suggesting that recombination and amplification of the T‐DNA occurred in maize cells. Mutant versions of the viral initiator gene (rep), known to be defective in the replication function, failed to generate recoverable recombinant T‐DNA molecules. Circularization of T‐DNA by the FLP/FRTsite‐specific recombination system and/or homologous recombination was not necessary to recover circular T‐DNAs. However, replicating T‐DNAs appeared to be suitable substrates for site‐specific and homologous recombination. Among 33 T‐DNA border junctions sequenced, only one pair of identical junction sites was found implying that the population of circular T‐DNAs was highly heterogenous. Since no circular T‐DNA molecules were detected in treatments withoutrep, it suggested that T‐DNA recombination was linked to replication and might have been stimulated by this process. The border junctions observed in recombinant T‐DNA molecules were indicative of illegitimate recombination and were similar to left‐border recombination of T‐DNA into the genome after Agro‐mediated plant transformation. However, recombination between T‐DNA molecules differed from T‐DNA/genomic DNA junction sites in that few intact right borders were observed. The replicating T‐DNA molecules did not enhance genomic random integration of T‐DNA in the experimental configuration used for this study.