bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterisation of an Arabidopsis–Leptosphaeria maculans pathosystem: resistance partially requires camalexin biosynthesis and is independent of salicylic acid, ethylene and jasmonic acid signalling
Authors: Bohman Svante , Staal Jens , Thomma Bart P. H. J. , Wang Maolin , Dixelius Christina 
Published: December 2003

SummaryOut of 168 Arabidopsis accessions screened with isolates of Leptosphaeria maculans, one (An‐1) showed clear disease symptoms. In order to identify additional components involved in containment of L. maculans in Arabidopsis, a screen for L. maculans‐susceptible (lms) mutants was performed. Eleven lms mutants were isolated, which displayed differential susceptibility responses to L. maculans. lms1 was crossed with Columbia (Col‐0) and Ws‐0, and mapping data for both populations showed the highest linkage to a region on chromosome 2. Reduced levels of PR‐1 and PDF1.2 expression were found in lms1 compared to wild‐type plants 48 h after pathogen inoculation. In contrast, the lms1 mutant displayed upregulation of either marker gene upon chemical treatment, possibly as an effect of an altered ethylene (ET) response. To assess the contribution of different defence pathways, genotypes implicated in salicylic acid (SA) signalling plants expressing the bacterial salicylate hydroxylase (nahG) gene, non‐expressor of PR1 (npr1)‐1 and phytoalexin‐deficient (pad4‐1), jasmonic acid (JA) signalling (coronatine insensitive (coi)1‐16, enhanced disease susceptibility (eds)8‐1 and jasmonic acid resistant (jar)1‐1) and ET signalling (eds4‐1, ethylene insensitive (ein)2, ein3‐1 and ethylene resistant (etr)1‐1) were screened. All the genotypes screened were as resistant as wild‐type plants, demonstrating the dispensability of the pathways in L. maculans resistance. When mutants implicated in cell death responses were assayed, responsive to antagonist 1 (ran1)‐1 exhibited a weak susceptible phenotype, whereas accelerated cell death (acd)1‐20 showed a rapid lesion development. Camalexin is only partially responsible for L. maculans containment in Arabidopsis, as pad3‐1 and enhanced susceptibility to Alternaria (esa)1 clearly showed a susceptible response while wild‐type levels of camalexin were present in An‐1 and lms1. The data presented point to the existence of multiple defence mechanisms controlling the containment of L. maculans in Arabidopsis.
Potato lectin: an updated model of a unique chimeric plant protein
Authors: Van Damme Els J. M. , Barre Annick , Rougé Pierre , Peumans Willy J. 
Published: December 2003

SummaryA complete cDNA encoding a potato tuber lectin has been identified and sequenced. Based on the deduced amino acid sequence, the still enigmatic molecular structure of the classical chimeric potato lectin could eventually be determined. Basically, the potato lectin consists of two nearly identical chitin‐binding modules, built up of two in‐tandem arrayed hevein domains that are interconnected by an extensin‐like domain of approximately 60 amino acid residues. Although this structure confirms the ‘canonical’ chimeric nature of the Solanaceae lectins, it differs fundamentally from all previously proposed models. The new insights in the structure are also discussed in view of the physiological role of the Solanaceae lectins.
Isolation of AtSUC2 promoter‐GFP‐marked companion cells for patch‐clamp studies and expression profiling
Authors: Ivashikina Natalya , Deeken Rosalia , Ache Peter , Kranz Erhard , Pommerrenig Benjamin , Sauer Norbert , Hedrich Rainer 
Published: December 2003

SummaryK+ channels control K+ homeostasis and the membrane potential in the sieve element/companion cell complexes. K+ channels from Arabidopsis phloem cells expressing green fluorescent protein (GFP) under the control of the AtSUC2 promoter were analysed using the patch‐clamp technique and quantitative RT‐PCR. Single green fluorescent protoplasts were selected after being isolated enzymatically from vascular strands of rosette leaves. Companion cell protoplasts, which could be recognized by their nucleus, vacuole and chloroplasts, and by their expression of the phloem‐specific marker genes SUC2 and AHA3, formed the basis for a cell‐specific cDNA library and expressed sequence tag (EST) collection. Although we used primers for all members of the Shaker K+ channel family, we identified only AKT2, KAT1 and KCO6 transcripts. In addition, we also detected transcripts for AtPP2CA, a protein phosphatase, that interacts with AKT2/3. In line with the presence of the K+ channel transcripts, patch‐clamp experiments identified distinct K+ channel types. Time‐dependent inward rectifying K+ currents were activated upon hyperpolarization and were characterized by a pronounced Ca2+‐sensitivity and inhibition by protons. Whole‐cell inward currents were carried by single K+‐selective channels with a unitary conductance of approximately 4 pS. Outward rectifying K+ channels (approximately 19 pS), with sigmoidal activation kinetics, were elicited upon depolarization. These two dominant phloem K+ channel types provide a versatile mechanism to mediate K+ fluxes required for phloem action and potassium cycling.
Nuclear localization and in vivo dynamics of a plant‐specific serine/arginine‐rich protein
Authors: Ali Gul Shad , Golovkin Maxim , Reddy Anireddy S. N. 
Published: December 2003

SummarySerine/arginine‐rich (SR) proteins in non‐plant systems are known to play important roles in both constitutive and alternative splicing of pre‐messenger RNAs (pre‐mRNAs). Recently, we isolated a novel SR protein (SR45), which interacts with U1 snRNP 70K protein, a key protein involved in 5′ splice site recognition. SR45 is found only in plants and is unique in having two SR domains separated by an RNA recognition motif (RRM). To study the localization and dynamics of SR45, we expressed it as a fusion to green fluorescent protein (GFP) in cultured cells and transgenic Arabidopsis plants. The SR45 is localized exclusively to nuclei. In interphase nuclei, GFP–SR45 was found both in speckles and nucleoplasm. The speckles exhibited intranuclear movements and changes in morphology. Inhibition of transcription and protein phosphorylation resulted in redistribution of SR45 to bigger speckles. The change in the number and morphology of speckles caused by inhibition of transcription was blocked by an inhibitor of phosphatases. These results indicate that transcription activity of the cell and protein (de)phosphorylation regulate the intranuclear distribution of SR45.
KINKY POLLEN encodes a SABRE‐like protein required for tip growth in Arabidopsis and conserved among eukaryotes
Authors: Procissi A. , Guyon A. , Pierson E. S. , Giritch A. , Knuiman B. , Grandjean O. , Tonelli C. , Derksen J. , Pelletier G. , Bonhomme S. 
Published: December 2003

SummaryIn higher plants, pollen tubes and root hairs share an ancient growth process named tip growth. We have isolated three allelic Arabidopsis mutant lines showing kinky‐shaped pollen tubes and, when homozygous, showing shorter and thicker root hairs. The ultrastructure of pollen tubes in these kinky pollen (kip) mutants is similar to that of the wild type; however, time‐lapse studies suggest that aberrant pollen tube shape is caused by periodic growth arrests alternated with phases of tube axis reorientation. The KIP gene encodes a protein of 2587 amino acids that is predicted to be targeted to the secretory pathway. KIP mRNA was detected in all organs investigated but was most abundant in pollen and roots. KIP has putative homologues in many eukaryotes, including mammals and yeast, and is similar to the Arabidopsis SABRE gene, whose mutation causes a dwarf phenotype. The phenotype of the kip/sab double mutant suggests related functions for both genes, however, the KIP protein is mostly required for tip‐growth.
An ancient R gene from the wild potato species Solanum bulbocastanum confers broad‐spectrum resistance to Phytophthora infestans in cultivated potato and tomato
Authors: Van Der Vossen Edwin , Sikkema Anne , Hekkert Bas te Lintel , Gros Jack , Stevens Patricia , Muskens Marielle , Wouters Doret , Pereira Andy , Stiekema Willem , Allefs Sjefke 
Published: December 2003

SummaryLate blight, caused by the oomycete pathogen Phytophthora infestans, is the most devastating disease for potato cultivation. Here, we describe the positional cloning of the Rpi‐blb1 gene from the wild potato species Solanum bulbocastanum known for its high levels of resistance to late blight. The Rpi‐blb1 locus, which confers full resistance to complex isolates of P. infestans and for which race specificity has not yet been demonstrated, was mapped in an intraspecific S. bulbocastanum population on chromosome 8, 0.3 cM from marker CT88. Molecular analysis of a bacterial artificial chromosome (BAC) clone spanning the Rpi‐blb1 locus identified a cluster of four candidate resistance gene analogues of the coiled coil, nucleotide‐binding site, leucine‐rich repeat (CC‐NBS‐LRR) class of plant resistance (R) genes. One of these candidate genes, designated the Rpi‐blb1 gene, was able to complement the susceptible phenotype in a S. tuberosum and tomato background, demonstrating the potential of interspecific transfer of broad‐spectrum late blight resistance to cultivated Solanaceae from sexually incompatible host species. Paired comparisons of synonymous and non‐synonymous nucleotide substitutions between different regions of Rpi‐blb1 paralogues revealed high levels of synonymous divergence, also in the LRR region. Although amino acid diversity between Rpi‐blb1 homologues is centred on the putative solvent exposed residues of the LRRs, the majority of nucleotide differences in this region have not resulted in an amino acid change, suggesting conservation of function. These data suggest that Rpi‐blb1 is relatively old and may be subject to balancing selection.
CSP41a, a multifunctional RNA‐binding protein, initiates mRNA turnover in tobacco chloroplasts
Authors: Bollenbach Thomas J. , Tatman Dana A. , Stern David B. 
Published: December 2003

SummaryExpression of chlorplast stem‐loop binding protein (CSP)41a, a highly conserved chloroplast endoribonuclease, was reduced >90% by the expression of antisense RNA in Nicotiana tabacum. The most striking effects of this silencing were two‐ to sevenfold decreases in the degradation rates of rbcL, psbA, and petD transcripts in lysed chloroplast extracts. These results are consistent with the hypothesis that CSP41a participates in initiating mRNA turnover through endonucleolytic cleavages. Surprisingly, rbcL and psbA mRNAs accumulated to similar levels in wild‐type and antisense lines. This suggested that decreased degradation was compensated by reduced transcription, which was confirmed using run‐on transcription assays. The collective accumulation of petD‐containing mRNAs in antisense plants decreased by 25% compared to wild‐type controls. However, the relative levels of petD processing intermediates in wild‐type and antisense plants did not differ, and there were no changes in petD 3′‐end maturation, suggesting that CSP41a is not required for petD RNA processing. CSP41a is a Mg2+‐dependent enzyme; therefore, extracts from antisense plants were tested at different Mg2+ concentrations. These experiments showed that the half‐life of rbcL decreased as the Mg2+ concentration was reduced, and at <1 mm free Mg2+, conditions where CSP41a is nearly inactive in vitro, the rbcL degradation rate was similar in wild‐type and antisense extracts, suggesting that CSP41a is normally bypassed under these conditions. Mg2+ has been shown to mediate RNA stability during chloroplast biogenesis, and our data suggest that regulation of CSP41a activity by Mg2+ is a component of this process.
Overexpression of the rice Osmyb4 gene increases chilling and freezing tolerance of Arabidopsis thaliana plants
Authors: Vannini Candida , Locatelli Franca , Bracale Marcella , Magnani Enrico , Marsoni Milena , Osnato Michela , Mattana Monica , Baldoni Elena , Coraggio Immacolata 
Published: December 2003

SummaryThe expression of the gene Osmyb4, detected at low level in rice (Oryza sativa) coleoptiles grown for 3 days at 29°C, is strongly induced by treatments at 4°C. At sublethal temperatures of 10 and 15°C, its expression in rice seedlings is already evident, but this effect cannot be vicariated by other stresses or ABA treatment. We demonstrate by transient expression that Myb4 transactivates the PAL2, ScD9 SAD and COR15a cold‐inducible promoters. The Osmyb4 function in vivo is demonstrated overexpressing its cDNA in Arabidopsis thaliana plants (ecotype Wassilewskija) under the control of the constitutive CaMV 35S promoter. Myb4 overexpressing plants show a significant increased cold and freezing tolerance, measured as membrane or Photosystem II (PSII) stability and as whole plant tolerance. Finally, in Osmyb4 transgenic plants, the expression of genes participating in different cold‐induced pathways is affected, suggesting that Myb4 represents a master switch in cold tolerance.
Organisation of the pantothenate (vitamin B5) biosynthesis pathway in higher plants
Authors: Ottenhof Harald H. , Ashurst Jennifer L. , Whitney Heather M. , Saldanha S. Adrian , Schmitzberger Florian , Gweon Hyun Soon , Blundell Tom L. , Abell Chris , Smith Alison G. 
Published: December 2003

SummaryPantothenate (vitamin B5) is the precursor for the biosynthesis of the phosphopantetheine moiety of coenzyme A and acyl carrier protein, and is synthesised in Escherichia coli by four enzymic reactions. Ketopantoate hydroxymethyltransferase (KPHMT) and pantothenate synthetase (PtS) catalyse the first and last steps, respectively. Two genes encoding KPHMT and one for PtS were identified in the Arabidopsis thaliana genome, and cDNAs for all three genes were amplified by PCR. The cDNAs were able to complement their respective E. coli auxotrophs, demonstrating that they encoded functional enzymes. Subcellular localisation of the proteins was investigated using green fluorescent protein (GFP) fusions and confocal microscopy. The two KPHMT–GFP fusion proteins were targeted exclusively to mitochondria, whereas PtS–GFP was found in the cytosol. This implies that there must be transporters for pathway intermediates. KPHMT enzyme activity could be measured in purified mitochondria from both pea leaves and Arabidopsis suspension cultures. We investigated whether Arabidopsis encoded homologues of the remaining two pantothenate biosynthesis enzymes from E. coli, l‐aspartate‐α‐decarboxylase (ADC) and ketopantoate reductase (KPR). No homologue of ADC could be identified using either conventional blast or searches with the program fugue in which the structure of the E. coli ADC was compared to all the annotated proteins in Arabidopsis. ADC also appears to be absent from the genome of the yeast, Saccharomyces cerevisiae, by the same criteria. In contrast, a putative Arabidopsis oxidoreductase with some similarity to KPR was identified with fugue.
Dual functionality of a plant U‐rich intronic sequence element
Authors: Simpson Craig G. , Jennings S. Nikki , Clark Gillian P. , Thow Graham , Brown John W. S. 
Published: December 2003

SummaryIn potato invertase genes, the constitutively included, 9‐nucleotide (nt)‐long mini‐exon requires a strong branchpoint and U‐rich polypyrimidine tract for inclusion. The strength of these splicing signals was demonstrated by greatly enhanced splicing of a poorly spliced intron and by their ability to support splicing of an artificial mini‐exon, following their introduction. Plant introns also require a second splicing signal, UA‐rich intronic elements, for efficient intron splicing. Mutation of the branchpoint caused loss of mini‐exon inclusion without loss of splicing enhancement, showing that the same U‐rich sequence can function as either a polypyrimidine tract or a UA‐rich intronic element. The distinction between the splicing signals depended on intron context (the presence or absence of an upstream, adjacent and functional branchpoint), and on the sequence context of the U‐rich elements. Polypyrimidine tracts tolerated C residues while UA‐rich intronic elements tolerated As. Thus, in plant introns, U‐rich splicing elements can have dual roles as either a general plant U‐rich splicing signal or a polypyrimidine tract. Finally, overexpression of two different U‐rich binding proteins enhanced intron recognition significantly. These results highlight the importance of co‐operation between splicing signals, the importance of other nucleotides within U‐rich elements for optimal binding of competing splicing factors and effects on splicing efficiency of U‐rich binding proteins.
A mutation in the nuclear‐encoded plastid ribosomal protein S9 leads to early embryo lethality in maize
Authors: Ma Zhengrong , Dooner Hugo K. 
Published: December 2003

SummarySeeds of the lethal embryo 1 (lem1) mutant in maize (Zea mays) display a non‐concordant lethal phenotype: whereas the embryo aborts very early, before the transition stage, the endosperm develops almost normally. The mutant was identified in a collection of maize lines that carried the transposon Activation (Ac) at different locations in the genome. Co‐segregation and reversion analysis showed that lem1 was tagged by Ac. The lem1 gene encodes a protein that is highly similar to the rice plastid 30S ribosomal protein S9 (PRPS9). lem1 maps to chromosome 1L and appears to be the only copy of prps9 in the maize genome. Green fluorescent protein (GFP) fusion constructs containing only the putative transit peptide (TP) of LEM1 localize exclusively to the plastids, confirming that the LEM1 protein is a PRP. In contrast, GFP fusion constructs containing the entire LEM1 protein co‐localize to the plastids and to the nucleus, suggesting a possible dual function for this protein. Two alternative, although not mutually exclusive, explanations are considered for the lem phenotype of the lem1 mutant: (i) functional plastids are required for normal embryo development; and (ii) the PRPS9 has an extra‐ribosomal function required for embryogenesis.
Expression of cytokinin biosynthetic isopentenyltransferase genes in Arabidopsis: tissue specificity and regulation by auxin, cytokinin, and nitrate
Authors: Miyawaki Kaori , Matsumoto‐Kitano Miho , Kakimoto Tatsuo 
Published: December 2003

SummaryThe rate‐limiting step of cytokinin biosynthesis in Arabidopsis thaliana Heynh. is catalyzed by ATP/ADP isopentenyltransferases, A. thaliana IsoPentenyl Transferase (AtIPT)1, and AtIPT4, and by their homologs AtIPT3, AtIPT5, AtIPT6, AtIPT7, and AtIPT8. To understand the dynamics of cytokinins in plant development, we comprehensively analyzed the expression of isopentenyltransferase genes of Arabidopsis. Examination of their mRNA levels and the expression patterns of the beta‐glucuronidase (GUS) gene fused to the regulatory sequence of each AtIPT gene revealed a specific expression pattern of each gene. The predominant expression patterns were as follows: AtIPT1::GUS, xylem precursor cell files in the root tip, leaf axils, ovules, and immature seeds; AtIPT3::GUS, phloem tissues; AtIPT4::GUS and AtIPT8::GUS, immature seeds with highest expression in the chalazal endosperm (CZE); AtIPT5::GUS, root primordia, columella root caps, upper part of young inflorescences, and fruit abscission zones; AtIPT7::GUS, endodermis of the root elongation zone, trichomes on young leaves, and some pollen tubes. AtIPT1, AtIPT3, AtIPT5, and AtIPT7 were downregulated by cytokinins within 4 h. AtIPT5 and AtIPT7 was upregulated by auxin within 4 h in roots. AtIPT3 was upregulated within 1 h after an application of nitrate to mineral‐starved Arabidopsis plants. The upregulation by nitrate did not require de novo protein synthesis. We also examined the expression of two genes for tRNA isopentenyltransferases, AtIPT2 and AtIPT9, which can also be involved in cytokinin biosynthesis. They were expressed ubiquitously, with highest expression in proliferating tissues. These findings are discussed in relation to the role of cytokinins in plant development.
Coastal Fish Diversity in Three Marine Protected Areas and One Unprotected Area in the Gulf of Trieste (Northern Adriatic)
Authors: Lipej Lovrenc , Bonaca Martina Orlando , Šiško Milijan 
Published: December 2003

Abstract.  The coastal fish assemblage in three protected sites and one unprotected area in the Slovenian part of the Gulf of Trieste (Northern Adriatic) was studied. Species composition and richness were comparable at all studied sites, including the control, unprotected area. Differences in fish density between the protected area of Debeli rtič and the unprotected area of Fiesa‐Pacug were revealed using correspondence analysis. Particularly the densities of certain labrid species (Symphodus cinereus and S. roissali) were higher in the protected area. Those differences are attributable to the extended and densely vegetated infralittoral belt of the Debeli rtič area rather than to its protected status.
Individual Variation in the Covering Behaviour of the Shallow Water Sea Urchin Paracentrotus lividus
Authors: Crook Anne C. 
Published: December 2003

Abstract.  A number of recent field‐based studies have investigated the possible functions of covering behaviour in a range of echinoid species. Some of these have found important relationships between covering behaviour and environmental factors, such as light (in particular, ultra‐violet light) and covering item availability. However, these studies have often shown considerable within‐species variation, thus making covering functionality both within and between species difficult to interpret. The present study experimentally investigates individual variability in covering behaviour characteristics of the sea urchin Paracentrotus lividus (Lamarck). Data were collected bimonthly over a 1‐year period at Lough Hyne, Ireland, by observing P. lividus in outdoor aquaria. Significant variations in covering behaviour characteristics were observed as a function of individual size and mobility but not as a function of sex. A significant relationship between water temperature, mobility and covering behaviour was also found and is hypothesized to have implications for grazing activity in P. lividus. In contrast to previous field studies of P. lividus at Lough Hyne, no summer ‘peak’ in the proportion of individuals covering was observed. However, there was a significant relationship between local solar radiation and ‘time to first cover’. Overall, these data highlight (i) the ecological significance of individual variation in P. lividus covering behaviour and (ii) the importance of investigating multiple factors as potential determinants of echinoid covering behaviour.