The Musculature of <Emphasis Type="Italic">Testudinella patina</Emphasis> (Rotifera: Flosculariacea), Revealed with CLSM

The musculature of Testudinella patina was visualized using phalloidin-linked fluorescent dye by confocal laser scanning microscopy. The conspicuous broad retractors appear to be made up of five separate fibers, of which three anchor in the neck region whereas two extend into the corona. Besides the broad retractors, a total of five paired longitudinal retractors are present and all of them extend into the corona. Incomplete circular muscles are found in groups in the neck region and in the medial and posterior parts of the trunk. The foot musculature comprises eight thin ventral foot muscles and six thicker dorsal foot muscles that all extend from the foot basis to the distal part of the foot. At the basis of the foot, each of the dorsal foot muscles anchors on a smaller, S-shaped subterminal foot muscle. The foot musculature furthermore comprises one pair of paraterminal foot muscles that each anchors basally on a subterminal foot muscle, extends into the most proximal part of the foot and attaches on one of the dorsal foot muscles. The visceral musculature is composed of extremely delicate fibers and is restricted to an area around and posterior to the foot opening. The presence of incomplete circular muscles supports that these muscles are a basal trait for Rotifera, whereas the morphology of the broad retractors and foot muscles is much more specialized and may be autapomorphic for Testudinella or alternatively for this genus and its closest relatives. The present results stress that revealing muscles by staining may produce new information from even well-investigated species, and that this information may contribute to a better understanding of functional as well as phylogenetic aspects of rotifer biology.     

Distribution of similar self-incompatibility (<Emphasis Type="Italic">S</Emphasis>) haplotypes in different genera,<Emphasis Type="Italic"> Raphanus</Emphasis> and<Emphasis Type="Italic"> Brassica</Emphasis>

The nucleotide sequences of ten SP11 and nine SRK alleles in Raphanus sativus were determined, and deduced amino acid sequences were compared with those of Brassica SP11 and SRK. The amino acid sequence identity of class-I SP11s in R. sativus was about 30% on average, the highest being 52.2%, while that of the S domain of class-I SRK was 77.0% on average and ranged from 70.8% to 83.9%. These values were comparable to those of SP11 and SRK in Brassica oleracea and B. rapa. SP11 of R. sativus S-21 was found to be highly similar to SP11 of B. rapa S-9 (89.5% amino acid identity), and SRK of R. sativus S-21 was similar to SRK of B. rapa S-9 (91.0%). SP11 and SRK of R. sativus S-19 were also similar to SP11 and SRK of B. oleracea S-20, respectively. These similarities of both SP11 and SRK alleles between R. sativus and Brassica suggest that these S haplotype pairs originated from the same ancestral S haplotypes.     

Musculature and nervous system of<Emphasis Type="Italic"> Gnathostomula peregrina</Emphasis> (Gnathostomulida) shown by phalloidin labeling,immunohistochemistry, and cLSM,and their phylogenetic significance

Musculature and nervous system of Gnathostomula peregrina (Gnathostomulida, Scleroperalia) were reconstructed from whole animals by immunohistochemistry and confocal laser scanning microscopy. The F-actin muscular subset, stained with FITC-labeled phalloidin, consists of: (1) eleven pairs (four ventral, one ventrolateral, one dorsolateral, five dorsal) of longitudinal muscles; (2) two types of diagonal muscles (thin fibers throughout the body, and slightly thicker fibers of which seven pairs occur ventrally and two pairs dorsally); (3) evenly spaced thin circular fibers that gird the posterior half of the body, continuing less prominently into the anterior half; and (4) a complex pharyngeal and genital musculature. Dorsoventral muscles are absent. The organization of the FMRFamidergic nervous system shows: (1) a central nervous system with a frontal ganglion and one pair of longitudinal nerves ending in a terminal commissure, and one median ventral nerve; (2) eight to ten unipolar perikarya above, and up to ten bipolar perikarya in front of the brain; (3) a total of five (one unpaired, two paired) longitudinal nerves of the peripheral nervous system with two to four accompanying perikarya; and (4) a buccal ganglion of the stomatogastric nervous system with six to eight perikarya above the pharyngeal bulbus. Our results reveal the musculature and nervous system of Gnathostomula to be more complex than hitherto reported.     

Reconstruction of the musculature of <Emphasis Type="Italic">Magelona</Emphasis> cf. <Emphasis Type="Italic">mirabilis</Emphasis> (Magelonidae) and <Emphasis Type="Italic">Prionospio cirrifera</Emphasis> (Spionidae) (Polychaeta,Annelida) by phalloidin labeling and cLSM

Recent investigations have suggested that a lack of circular muscle fibers may be a common situation rather than a rare exception in polychaetes. As part of a comparative survey of polychaete muscle systems, the F-actin musculature subset of Magelona cf. mirabilis and Prionospio cirrifera were labeled with phalloidin and three-dimensionally analyzed and reconstructed by means of cLSM. Obvious similarities are sublongitudinal lateral, circumbuccal, palp retractor, dominating dorsal longitudinal, perpendicular lateral and ventral transverse muscles. Differences between M. cf. mirabilis and P. cirrifera are: (1) two types of prostomial muscles (transversal and longitudinal) in M. cf. mirabilis versus one type (diagonal) in P. cirrifera; (2) one type of palp muscles (longitudinal) in M. cf. mirabilis versus three types (longitudinal, diagonal, circular) in P. cirrifera; (3) five ventral longitudinal muscles (ventromedian, paramedian, ventral) in M. cf. mirabilis versus four (two paramedian, two ventral) in P. cirrifera. Ventral and lateral transverse fibers are present in the thorax, but absent in the abdomen of M. cf. mirabilis. The triangular lumen of the pharynx in M. cf. mirabilis is surrounded by radial muscle fibers; three sets of pharynx diductors attach to its dorsal side. The unique features of P. cirrifera are one pair of brain muscles and segmentally arranged dorsal transverse muscles, the latter located outside the longitudinal muscles. The transverse lateral muscles are restricted to the sides and lie beneath the longitudinal muscles, a pattern described here for the first time. A true, outer layer of circular fibers is absent in both species of Spionida that were investigated.     

Identification and genomic distribution of<Emphasis Type="Italic"> gypsy</Emphasis> like retrotransposons in<Emphasis Type="Italic"> Citrus</Emphasis> and<Emphasis Type="Italic"> Poncirus</Emphasis>

Transposable elements might be importantly involved in citrus genetic instability and genome evolution. The presence of gypsy like retrotransposons, their heterogeneity and genomic distribution in Citrus and Poncirus, have been investigated. Eight clones containing part of the POL coding region of gypsy like retrotransposons have been isolated from a commercial variety of Citrus clementina, one of the few sexual species in Citrus. Four of the eight clones might correspond to active elements given that they present all the conserved motifs described in the literature as essential for activity, no in-frame stop codon and no frame-shift mutation. High homology has been found between some of these citrus elements and retroelements within a resistance-gene cluster from potato, another from Poncirus trifoliata and two putative resistance polyproteins from rice. Nested copies of gypsy like elements are scattered along the Citrus and Poncirus genomes. The results on genomic distribution show that these elements were introduced before the divergence of both genera and evolved separately thereafter. IRAPs based on gypsy and copia types of retrotransposons seem to distribute differently, therefore gypsy based IRAPs prove a new, complementary set of molecular markers in Citrus to study and map genetic variability, especially for disease resistance. Similarly to copia-derived IRAPs, the number of copies and heterozygosity values found for gypsy derived IRAPs are lower in Poncirus than in Citrus aurantium, which is less apomictic and the most usual rootstock for clementines until 1970.Communicated by C. Möllers     

Molecular genetics of the<Emphasis Type="Italic"> Alhambra</Emphasis> (<Emphasis Type="Italic"> Drosophila AF10</Emphasis>) complex locus of<Emphasis Type="Italic"> Drosophila</Emphasis>

The Alhambra ( Alh) gene is the Drosophila homologue of the human AF10 gene. AF10 has been identified as a fusion partner of MLL, a human homologue of the fly gene trithorax, in infant leukemias. The endogenous function of human AF10 is not known, but may be vital to its role in acute leukemia. This prompted us to analyse Alh function. We describe here the genetic organisation of the Alh locus in D. melanogaster. We show that an independent lethal complementation group encoding a muscle protein ( Mlp84B) is located within an Alh intron. We have already shown that the leucine zipper (LZ) domain of ALH activates several Polycomb group-responsive elements. We further demonstrate that the LZ domain on its own bears the Alh vital function, since it is necessary and sufficient for rescue of Alh mutant lethality. Finally, we demonstrate that, in contrast to a previous report, Alh does not affect position-effect variegation.Communicated by G. Reuter     

Comparative mapping reveals partial conservation of synteny at the apomixis locus in<Emphasis Type="Italic"> Paspalum</Emphasis> spp<Emphasis Type="Italic">.</Emphasis>

In plants, gametophytic apomixis is a form of asexual reproduction that leads to the formation of seed-derived offspring that are genetically identical to the mother plant. A common set of RFLP markers, including five rice anchor markers previously shown to be linked to apomixis in Paspalum simplex, were used to detect linkage with apomixis in P. notatum and P. malacophyllum. A comparative map of the region around the apomixis locus was constructed for the three Paspalum species, and compared to the rice map. The locus that controls apomixis in P. simplex was almost completely conserved in the closely related species P. malacophyllum, whereas it was only partially represented in the distantly related species P. notatum. Although strong synteny of markers was noted between this locus and a portion of rice chromosome 12 in both P. simplex and P. malacophyllum, the same locus in P. notatum was localized to a hybrid chromosome which carries markers that map to rice chromosomes 2 and 12. All three Paspalum species showed recombination suppression at the apomixis locus; in the case of P. notatum, this might be due to a heterozygosity for a translocation that most probably negatively interferes with chromosomal pairing near the locus. A common set of markers that show linkage with apomixis in all three Paspalum species define a portion of the apomixis-controlling locus that is likely to contain genes critical for apomictic reproduction.Communicated by R. Hagemann     

Adaptive changes in structure of skeletal muscles from adult <Emphasis Type="Italic">Sod1</Emphasis> homozygous knockout mice

Cu/Zn superoxide dismutase (SOD1), which is localized cytoplasmically and in the mitochondrial intermembrane space, is an enzyme that is critically important for superoxide free-radical elimination. Compared with age-matched wild-type littermates (Sod1 ^+/+ ), SOD1 homozygous knockout (Sod1 ^-/- ) mice have smaller body masses, heart and skeletal muscle masses, and muscle cross-sectional areas. At the light-microscopic level, cross sections of skeletal muscles from Sod1 ^-/- mice show no gross structural abnormalities. Following the staining of muscles of Sod1 ^-/- mice for succinate dehydrogenase (SDH) enzymatic activity, a grouping of SDH-positive fibers has been observed. Immunostaining for neural cell adhesion marker in the gastrocnemius muscle of Sod1 ^-/- mice has revealed a small number of atrophic denervated muscle fibers. No denervated fibers are observed in extensor digitorum longus (EDL), tibialis anterior, or plantaris muscles. An increase in mRNA expression levels of myogenin and acetylcholine receptor alpha has been detected in muscles in Sod1 ^-/- mice, but no changes in MyoD expression occur. Compared with fast oxidative fibers in EDL muscles of Sod1 ^+/+ mice, those of Sod1 ^-/- mice show increased accumulations of sub-sarcolemmal mitochondria. We conclude that the lack of SOD1 in adult Sod1 ^-/- mice does not result in extensive denervation of skeletal muscle fibers, although the distribution of fiber types is modified, and that fast oxidative fibers develop alterations in the amount and spatial distribution of sub-sarcolemmal mitochondria. This study was supported by NIA grant PO1-AG20591, by the Nathan Shock Center Contractility Core (NIA grant P30-AG13283), and by a Nathan Shock Center Pilot Award (to T. Kostrominova).     

Functional anatomy of the luring apparatus of the deep-sea ceratioid anglerfish <Emphasis Type="Italic">Cryptopsaras couesii</Emphasis> (Lophiiformes: Ceratiidae)

The osteology and myology of the illicial apparatus of Cryptopsaras couesii were examined in an effort to elucidate function. The apparatus consists of two bones, a tiny illicial bone, completely enveloped by tissue of the esca, and an extremely long supporting pterygiophore that lies within a deep groove on the dorsal surface of the head. The anterior end of the pterygiophore emerges on the tip of the snout from between the frontal bones, while the posterior end, encased in a dermal sheath when the illicial apparatus is retracted, emerges on the back just anterior to the dorsal caruncles. Five pairs of muscles control movement of the illicial apparatus: small, short erectors and depressors control movement of the illicial bone, while extremely long inclinators, protractors, and retractors control movement of the pterygiophore. The protractors and retractors of C. couesii are more robust and much longer than those of other lophiiforms, indicating that the pterygiophore of this species has an exceptionally wide range of movement in the anterior and posterior plane. Moreover, these muscles wind around the pterygiophore in opposite directions, a unique anatomy that suggests that C. couesii extends and retracts the pterygiophore by rotation.     

Sex determination in<Emphasis Type="Italic"> Drosophila melanogaster</Emphasis> and<Emphasis Type="Italic"> Musca domestica</Emphasis> converges at the level of the terminal regulator<Emphasis Type="Italic"> doublesex</Emphasis>

Sex-determining cascades are supposed to have evolved in a retrograde manner from bottom to top. Wilkins 1995 hypothesis finds support from our comparative studies in Drosophila melanogaster and Musca domestica, two dipteran species that separated some 120 million years ago. The sex-determining cascades in these flies differ at the level of the primary sex-determining signal and their targets, Sxl in Drosophila and F in Musca. Here we present evidence that they converge at the level of the terminal regulator, doublesex (dsx), which conveys the selected sexual fate to the differentiation genes. The dsx homologue in Musca, Md-dsx, encodes male-specific (MdDSX^M) and female-specific (MdDSX^F) protein variants which correspond in structure to those in Drosophila. Sex-specific regulation of Md-dsx is controlled by the switch gene F via a splicing mechanism that is similar but in some relevant aspects different from that in Drosophila. MdDSX^F expression can activate the vitellogenin genes in Drosophila and Musca males, and MdDSX^M expression in Drosophila females can cause male-like pigmentation of posterior tergites, suggesting that these Musca dsx variants are conserved not only in structure but also in function. Furthermore, downregulation of Md-dsx activity in Musca by injecting dsRNA into embryos leads to intersexual differentiation of the gonads. These results strongly support a role of Md-dsx as the final regulatory gene in the sex-determining hierarchy of the housefly.Edited by D. Tautz     

The karyotype of the Azumi shrew<Emphasis Type="Italic">Sorex hosonoi</Emphasis>

Karyotype ofSorex hosonoi Imaizumi, 1954 from Mt. Asama in central Honshu, Japan, were examined with conventional staining and G-banding using ASG methods. The diploid and fundamental autosomal arm numbers were 42 and 66, respectively. The autosomes consisted of seven metacentric, six submetacentric, and seven acrocentric pairs. The sex chromosomes were large-sized acrocentric X and small-sized subtelocentric Y. The relationship between the karyotypes ofS. hosonoi andS. shinto was explained by one pericentric inversion at the no. 5 ofS. hosonoi and the no. 9 ofS. shinto. A rearrangement inS. shinto-hosonoi differed from the rearrangements occurring on no. 5 ofS. shinto-caecutiens/unguiculatus.     

Increase of CGRP Expression in Motor Endplates Within Fore and Hind Limb Muscles of the Degenerating Muscle Mouse (<Emphasis Type="Italic">Scn8a</Emphasis><Superscript><Emphasis Type="Italic">dmu</Emphasis></Superscript>)

The distribution of calcitonin gene-related peptide (CGRP) was examined in skeletal muscles of fore and hind limb as well as in oral and cranio-facial regions of the degenerating muscle (dmu) mouse, which harbours a null mutation in the voltage-gated sodium channel gene Scn8a. In limb, oral and cranio-facial muscles of wild type mice, only a few motor endplates contained CGRP-immunoreactivity. However, many CGRP-immunoreactive motor endplates appeared in the triceps brachii muscle, the biceps brachii muscle, the brachialis muscle, and the gastrocnemius muscle of dmu mice. CGRP-immunoreactive density of motor endplates in the skeletal muscles was also elevated by the mutation. In these muscles, the atrophy of muscle fibers could be detected and the density of cell nuclei in the musculature increased. In the flexor digitorum profundus muscle, the flexor digitorum superficialis muscle, and the soleus muscle as well as in oral and cranio-facial muscles, however, the distribution of CGRP-immunoreactivity was barely affected by the mutation. The morphology of muscle fibers and the distribution of cell nuclei within them were also similar in wild type and dmu mice. In the lumbar spinal cord of dmu mice, CGRP-immunoreactive density of spinal motoneurons increased. These findings suggest that the atrophic degeneration in some fore and hind limb muscles of dmu mice may increase CGRP expression in their motoneurons.     

Muscle fat composition of pheasants (<Emphasis Type="Italic">Phasianus colchicus)</Emphasis>, wild ducks (<Emphasis Type="Italic">Anas platyrhynchos</Emphasis>) and black coots (<Emphasis Type="Italic">Fulica atra</Emphasis>)

The aim of this investigation was to characterise the fatty acid composition within intramuscular fat (IMF) of two muscles (breast and thigh) from 28 pheasants, ten wild ducks and 27 black coots from Slovakia. A high variability for all single fatty acids (FA) and the total fat concentration in muscles of wild birds was identified. Black coots deposited the highest fat in breast muscle whereas wild ducks and pheasants accumulated more lipids in thigh muscle. In general, the content of polyunsaturated fatty acids (PUFA) of the IMF in wild bird muscles was high, and the saturated FA concentration was lower compared with muscles of domestic farm animals. The ratio between PUFA and saturated fatty acids (PSQ) ranked between 0.6 and 1.2, and the ratio of n-6/n-3 fatty acid was favourably low in black coot and wild pheasants (3.2 and 2.9, respectively). Farmed pheasants had increased IMF and more saturated and n-6 fatty acids deposited in thigh muscle but not in breast muscle.     

Expression pattern of<Emphasis Type="Italic"> INNER NO OUTER</Emphasis> homologue in<Emphasis Type="Italic"> Nymphaea</Emphasis> (water lily family,Nymphaeaceae)

Two homologues of INNER NO OUTER (INO) in Nymphaea alba and N. colorata (Nymphaeaceae) were isolated and the expression pattern of the N. alba INO homologue NaINO was examined by in situ hybridization. The INO homologues obtained have a portion similar to INO in the predicted amino acid sequences between the conserved zinc finger-like and YABBY domains. In an in situ hybridization analysis, NaINO is expressed in the outer epidermis of the outer integument, inner integument, and the tip of the nucellus. The pattern observed in the outer integument is very similar to that of Arabidopsis thaliana, while the expression in the inner integument and nucellus is not observed in A. thaliana.Edited by G. JürgensToshihiro Yamada is a Research Fellow of the Japan Society for the Promotion of Science     

Nervous and muscle system development in <Emphasis Type="Italic">Phascolion strombus</Emphasis> (Sipuncula)

Recent interpretations of developmental gene expression patterns propose that the last common metazoan ancestor was segmented, although most animal phyla show no obvious signs of segmentation. Developmental studies of non-model system trochozoan taxa may shed light on this hypothesis by assessing possible cryptic segmentation patterns. In this paper, we present the first immunocytochemical data on the ontogeny of the nervous system and the musculature in the sipunculan Phascolion strombus. Myogenesis of the first anlagen of the body wall ring muscles occurs synchronously and not subsequently from anterior to posterior as in segmented spiralian taxa (i.e. annelids). The number of ring muscles remains constant during the initial stages of body axis elongation. In the anterior-posteriorly elongated larva, newly formed ring muscles originate along the entire body axis between existing myocytes, indicating that repeated muscle bands do not form from a posterior growth zone. During neurogenesis, the Phascolion larva expresses a non-metameric, paired, ventral nerve cord that fuses in the mid-body region in the late-stage elongated larva. Contrary to other trochozoans, Phascolion lacks any larval serotonergic structures. However, two to three FMRFamide-positive cells are found in the apical organ. In addition, late larvae show commissure-like neurones interconnecting the two ventral nerve cords, while early juveniles exhibit a third, medially placed FMRFamidergic ventral nerve. Although we did not find any indications for cryptic segmentation, certain neuro-developmental traits in Phascolion resemble the conditions found in polychaetes (including echiurans) and myzostomids and support a close relationship of Sipuncula and Annelida.     

Spore ontogeny of the arbuscular mycorrhizal fungus<Emphasis Type="Italic"> Archaeospora trappei</Emphasis> (Ames &; Linderman) Morton &; Redecker (<Emphasis Type="Italic">Archaeosporaceae</Emphasis>)

Arbuscular mycorrhizal (AM) fungi in the genus Archaeospora (family Archaeosporaceae) contain both monomorphic and dimorphic species. The synanamorphism is often hard to discern without ontogenetic observations. Here, the spore ontogeny of Ar. trappei is reported from single species pot culture studies. The sporogenous hypha swelled up to a terminal sporiferous saccule and produced a lateral spore primordium on its neck. The saccule expanded fully before the spore primordium emerged. The saccule transferred its contents into the expanding spore and collapsed while wall differentiation continued inside the spore. The spore wall of Ar. trappei differentiated sequentially, in discrete steps, as in Acaulosporaceae members. In contrast, Ar. trappei produced a simplified spore wall in which the components differed in chemical and physical characteristics from those of the Acaulosporaceae members. Ontogenetic studies confirmed Ar. trappei to be monomorphic and producing acaulosporoid spores. The fungus is a new record to New Zealand.     

Three new coccidians (<Emphasis Type="Italic">Cyclospora</Emphasis>, <Emphasis Type="Italic">Eimeria</Emphasis>) from eastern moles, <Emphasis Type="Italic">Scalopus aquaticus</Emphasis> (Linnaeus) (Mammalia: Soricomorpha: Talpidae) from Arkansas,USA

Three new species of coccidians (Apicomplexa: Eimeriidae) are described from eastern moles, Scalopus aquaticus (Linnaeus) from Arkansas. Oöcysts of Cyclospora duszynskii n. sp. are subspheroidal with a smooth bi-layered wall, measure 11.4 × 10.0 µm, and have a length/width (L/W) ratio of 1.1; both micropyle and oöcyst residuum are absent, but a single polar granule is present. Sporocysts are ellipsoidal and measure 7.2 × 5.4 µm, L/W 1.3; an indistinct Stieda body is present, but the sub-Stieda and para-Stieda bodies are absent and the sporocyst residuum is composed of medium to large granules of different sizes along the edge of the sporocyst. Oöcysts of Cyclospora yatesi n. sp. are subspheroidal to ovoidal with an ornate outer wall, measure 17.0 × 15.2 µm, L/W 1.1; both micropyle and oöcyst residuum are absent, but a single polar granule is present. Sporocysts are ellipsoidal and measure 9.7 × 7.3 µm, L/W 1.3; an indistinct Stieda body is present, but sub-Stieda and para-Stieda bodies are absent and the sporocyst residuum is composed of medium to large granules of different sizes along the edge of the sporocyst. Oöcysts of Eimeria paulettefordae n. sp. are ovoidal to ellipsoidal with an ornate outer wall, measure 30.0 × 25.4 µm, L/W 1.2; both micropyle and oöcyst residuum are absent, but a single polar granule is present. Sporocysts are ellipsoidal and measure 12.6 × 9.2 µm, L/W 1.4; a button-like Stieda body is present, but sub-Stieda and para-Stieda bodies are absent and the sporocyst residuum is composed of medium to large granules of different sizes along the edge of the sporocyst. These are the first coccidians described from Arkansas populations of S. aquaticus. In addition, a summary is provided on the cyclosporans and eimerians from North American talpids.     

Rhamnolipid-producing thermophilic bacteria of species <Emphasis Type="Italic">Thermus</Emphasis> and <Emphasis Type="Italic">Meiothermus</Emphasis>

Novel rhamnolipid-producing strains of three thermophilic bacteria, Thermus sp., T. aquaticus and Meiothermus ruber were identified that have not been previously described as rhamnolipid producers. Rhamnolipids were extracted from supernatant and further purified by thin-layer chromatography. Mass spectrometry with negative electrospray ionization revealed 77 rhamnolipid homologues varying in chain length and unsaturation. Tandem mass spectrometry identified mono-rhamnolipid and di-rhamnolipid homologues containing one or two 3-hydroxy-fatty acids, saturated, monounsaturated or diunsaturated, even- or odd-chain, up to unusual long chains with 24 carbon atoms. The stereochemistry of rhamnose was L and that of 3-hydroxy-fatty acids was R, the position of double bonds in monoenoic acids was cis ω-9. All three strains produced a rhamnolipid that differs in structure from Pseudomonas aeruginosa rhamnolipids and exhibits excellent surfactant properties. Importantly, in comparison to P. aeruginosa both strains, i.e., Thermus and Meiothermus, are Biosafety level 1 microorganisms and are not pathogenic to humans.     

<Emphasis Type="Italic">PCC1</Emphasis>: a merging point for pathogen defence and circadian signalling in<Emphasis Type="Italic"> Arabidopsis</Emphasis>

Using a cDNA-array we identified expressed sequence tag 163B24T7 as rapidly up-regulated in Arabidopsis thaliana (L.) Heynh. after pathogen exposure. Detailed expression analysis revealed that the corresponding gene is up-regulated not only after exposure to avirulent Pseudomonas syringae pv. tomato but also to virulent strains. This up-regulation is dependent on functional salicylic acid defence-signalling pathways. Moreover, we found the gene was circadian-regulated, showing peaks of expression at the end of the day. Using plants overexpressing the clock component CCA1, we showed that the PCC1 gene is regulated by the inner clock of Arabidopsis. Accordingly, we named the gene PCC1, for pathogen and circadian controlled. PCC1 is a member of a novel family of six small polypeptides in Arabidopsis. A functional role for PCC1 in plant defence was demonstrated since plants overexpressing PCC1 are resistant against normally virulent oomycetes. Thus, PCC1 demonstrates a potential interrelationship between pathogen and circadian signalling pathways.Abbreviations cfu Colony-forming units - EST Expressed sequence tag - Pst Pseudomonas syringae pv. tomato - TAIR The Arabidopsis information resource     

<Emphasis Type="Italic">ZWILLE</Emphasis> buffers meristem stability in<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

The shoot apical meristem of higher plants consists of a population of stem cells at the tip of the plant body that continuously gives rise to organs such as leaves and flowers. Cells that leave the meristem differentiate and must be replaced to maintain the integrity of the meristem. The balance between differentiation and maintenance is governed both by the environment and the developmental status of the plant. In order to respond to these different stimuli, the meristem has to be plastic thus ensuring the stereotypic shape of the plant body. Meristem plasticity requires the ZWILLE (ZLL) gene. In zll mutant embryos, the apical cells are misspecified causing a variability of the meristems size and function. Using specific antibodies against ZLL, we show that the zll phenotype is due to the complete absence of the ZLL protein. In immunohistochemical experiments we confirm the observation that ZLL is solely localized in vascular tissue. For a better understanding of the role of ZLL in meristem stability, we analysed the genetic interactions of ZLL with WUSCHEL (WUS) and the CLAVATA1, 2 and 3 (CLV) genes that are involved in size regulation of the meristem. In a zll loss-of-function background wus has a negative effect whereas clv mutations have a positive effect on meristem size. We propose that ZLL buffers meristem stability non-cell-autonomously by ensuring the critical number of apical cells required for proper meristem function.Edited by G. JürgensAn erratum to this article can be found at