A Rhizobium tropici DNA region carrying the amino-terminal half of a nodD gene and a nod-box-like sequence confers host-range extension

Rhizobium tropici CIAT899 is a broad-host-range strain that, in addition to Phaseolus, nodulates other plant legumes such as Leucaena and Macroptilium. The narrow-host-range of Rhizobium leguminosarum biovars phaseoli (strain CE3) and trifolii (strain RS1051) can be extended to Leucaena esculents and Phaseolus vulgaris plants, respectively, by the introduction of a DNA fragment 521 bp long, which carries 128 amino acids of the amino-terminal region of a nodD gene from R. tropici, as well as a putative nod-box-like sequence, divergently oriented. The 521 bp fragment, in the presence of L. esculenta or P. vulgaris root exudates, induced a R. leguminosarum bv. viciae nodA-lacZ fusion in either a CE3 or RS1051 background, respectively.     

Molecular Cloning and Characterization of <Emphasis Type="Italic">nodD</Emphasis> Genes from <Emphasis Type="Italic">Rhizobium</Emphasis> sp. SIN-1, a Nitrogen-Fixing Symbiont of <Emphasis Type="Italic">Sesbania</Emphasis> and Other Tropical Legumes

Rhizobium sp. SIN-1, a nitrogen-fixing symbiont of Sesbania aculeata and other tropical legumes, carries two copies of nodD, both on a sym plasmid. We have isolated these two nodD genes by screening a genomic library of Rhizobium sp. SIN-1 with a nodD probe from Sinorhizobium meliloti. Nucleotide sequence and the deduced amino acid sequence analysis indicated that the nodD genes of Rhizobium sp. SIN-1 are most closely related to those of R. tropici and Azorhziobium caulinodans. Rhizobium sp. SIN-1 nodD1 complemented a S. meliloti nodD1D2D3 negative mutant for nodulation on alfalfa, but failed to complement a nodD1 mutant of S. fredii USDA191 for soybean nodulation. A hybrid nodD gene, containing the N-terminus of S. fredii USDA191 nodD1 and the C-terminus of Rhizobium sp. SIN-1 nodD1, complemented the nodD1 negative mutant of USDA191 for nodulation on soybean. Received: 17 January 2002 / Accepted: 18 February 2002     

Multiple Bacteriocin Production by Leuconostoc mesenteroidesTA33a and Other Leuconostoc/Weissella Strains

Leuconostoc (Lc.) mesenteroides TA33a produced three bacteriocins with different inhibitory activity spectra. Bacteriocins were purified by adsorption/desorption from producer cells and reverse phase high-performance liquid chromatography. Leucocin C-TA33a, a novel bacteriocin with a predicted molecular mass of 4598 Da, inhibited Listeria and other lactic acid bacteria (LAB). Leucocin B-TA33a has a predicted molecular mass of 3466 Da, with activity against Leuconostoc/Weissella (W.) strains, and appears similar to mesenterocin 52B and dextranicin 24, while leucocin A-TA33a, which also inhibited Listeria and other LAB strains, is identical to leucocin A-UAL 187. A survey of other known bacteriocin-producing Leuconostoc/Weissella strains for the presence of the three different bacteriocins revealed that production of leucocin A-, B- and C-type bacteriocins was widespread. Lc. carnosum LA54a, W. paramesenteroides LA7a, and Lc. gelidum UAL 187-22 produced all three bacteriocins, whereas W. paramesenteroides OX and Lc. carnosum TA11a produced only leucocin A- and B-type bacteriocins. Received: 11 April 1997 / Accepted: 10 June 1997     

A molecular and ultrastructural description of Spathidiopsis buddenbrocki and the phylogenetic position of the family Placidae (Ciliophora)

Spathidiopsis and Placus are the only two genera within the family Placidae. The family has been placed in the class Prostomatea and order Prorodontida because its members have somatic monokinetids with a radial transverse ribbon, a straight non‐overlapping postciliary ribbon, and anteriorly directed non‐overlapping kinetodesmal fibril, an apical cytostome lacking specialized oral cilia, a brosse, and toxicysts. To confirm the stability of this placement, ultrastructural morphology and small subunit rRNA gene sequences of Spathidiopsis socialis, Spathidiopsis buddenbrocki, and Placus striatus were determined. These data were combined with information from other ciliates, and phylogenetic trees were generated using maximum‐likelihood and maximum‐parsimony methods. The analyses confirmed the family Placidae to be a monophyletic group in the Prostomatea with the Placidae a sister group to a Cryptocaryon + Coleps + Prorodon clade.     

Phylogenetic assessment and biogeographic analyses of tribe <Emphasis Type="Italic">Peracarpeae</Emphasis> (Campanulaceae)

Peracarpeae is a small tribe consisting of three genera: Homocodon, Heterocodon and Peracarpa, with a disjunct distribution between eastern Asia and western North America. Homocodon is endemic to southwestern China and was previously placed in the western North American genus Heterocodon. Our phylogenetic analysis using four plastid markers (matK, atpB, rbcL and trnL-F) suggests the polyphyly of Peracarpeae. Homocodon is sister to a clade consisting of the eastern Asian Adenophora, Hanabusaya and species of Campanula from the Mediterranean region and North America, rather than forming a clade with Heterocodon. Homocodon and its Eurasia relatives are estimated to have diverged in the early Miocene (16.84 mya, 95% HPD 13.35–21.45 mya). The eastern Asian Peracarpa constitutes a clade with the North American Heterocodon, Githopsis and three species of Campanula, supporting a disjunction between eastern Asia and North America in Campanulaceae. The Asian-North American disjunct lineages diverged in the early Miocene (16.17 mya, 95% HPD 13.12–20.9 mya). The biogeographic analyses suggest that Homocodon may be a relict of an early radiation in eastern Asia, and that Peracarpa and its closest North American relatives most likely originated from a Eurasian ancestor.     

Morphology and development of anthers and ovules in Croton and Astraea (Euphorbiaceae)

We examined the embryological development of anthers and ovules from Astraea (A. lobata and A. praetervisa) and Croton (C. floribundus, C. fuscescens, C. glandulosus, C. lundianus, C. piptocalyx, C. urucurana and C. triqueter) focusing on features with systematic significance for the group. Some of these features are common in Euphorbiaceae including: a dicotyledonous type of anther wall formation, a secretory tapetum, a mixed origin of the outer ovule integument, an epidermal origin of the inner ovule integument, the occurrence of many archesporial cells inside the ovules and a megagametophyte of the Polygonum‐type. Other features, such as the presence of styloid crystals in the tapetum, an idioblast with a druse in the endothecium, simultaneous and successive microsporogenesis, and a functional micropylar megaspore, have not previously been reported in the family. These characters appear to distinguish Croton and Astraea from other Euphorbiaceae and possibly represents autapomorphies for the tribe Crotoneae.     

A molecular systematic study ofCathaya, a relic genus of thePinaceae in China

The systematic position ofCathaya, a relic genus of thePinaceae, was discussed based on therbcL gene sequence. The sequence data were analysed with PAUP and MEGA programs. The great genetic distance value betweenCathaya and any other genus of thePinaceae showed thatCathaya was a distinct and isolated genus. The most parsimonious Fitch tree and neighbor-joining tree showed thatCathaya was distantly related to the clade comprisingAbies, Keteleeria, Pseudolarix andTsuga, and a sister group relationship betweenCathaya andPinus was weakly supported.Pseudotsuga is closely related toLarix. In theAbies-Keteleeria-Pseudolarix-Tsuga clade,Abies has a close relationship toKeteleeria whilePseudolarix is relatively closely related toTsuga.     

A fragment of chloroplast DNA was transferred horizontally,probably from non-eudicots,to mitochondrial genome of <Emphasis Type="Italic">Phaseolus</Emphasis>

The mitochondrial genomes of some Phaseolus species contain a fragment of chloroplast trnA gene intron, named pvs-trnA for its location within the Phaseolus vulgaris sterility sequence (pvs). The purpose of this study was to determine the type of transfer (intracellular or horizontal) that gave rise to pvs-trnA. Using a PCR approach we could not find the respective portion of the trnA gene as a part of pvs outside the Phaseolus genus. However, a BLAST search revealed longer fragments of trnA present in the mitochondrial genomes of some Citrus species, Helianthus annuus and Zea mays. Basing on the identity or near-identity between these mitochondrial sequences and their chloroplast counterparts we concluded that they had relocated from chloroplasts to mitochondria via recent, independent, intracellular DNA transfers. In contrast, pvs-trnA displayed a relatively higher sequence divergence when compared with its chloroplast counterpart from Phaseolus vulgaris. Alignment of pvs-trnA with corresponding trnAfragments from 35 plant species as well as phylogenetic analysis revealed that pvs-trnA grouped with non-eudicot sequences and was well separated from all Fabalessequences. In conclusion, we propose that pvs-trnA arose via horizontal transfer of a trnA intron fragment from chloroplast of a non-eudicot plant to Phaseolus mitochondria. This is the first example of horizontal transfer of a chloroplast sequence to the mitochondrial genome in higher plants.     

A comparison of attack rates in a native and an introduced population of the parasitoid Cotesia glomerata

The attack rate of a population of the braconid parasitoid Cotesia glomerata, introduced into the USA over 100 years ago as a parasitoid of Pieris rapae, was compared with that of a native British population, which normally attacks P. brassicae, and with that of a P. rapae specialist, Cotesia rubecula. British C. glomerata attacked P. brassicae at a much higher rate than it attacked P. rapae. In comparison with British C. glomerata, C. rubecula showed a higher attack rate with P. rapae. American C. glomerata attacked P. rapae at a slightly higher rate than did British C. glomerata, but not at as high a rate as that achieved by C. rubecula. The differences in each comparison were statistically significant. The possible causes of the differences between British and American C. glomerata attacking P. rapae are discussed. They may be due to genetic or environmental effects. Egg load did not appear to be a factor limiting the number of hosts parasitized under the conditions of the experiments.     

The light-dependent regulator velvet A of <Emphasis Type="Italic">Aspergillus nidulans</Emphasis> acts as a repressor of the penicillin biosynthesis

The biosynthesis of the β-lactam antibiotic penicillin in Aspergillus nidulans is catalysed by three enzymes that are encoded by the genes acvA, ipnA and aatA. Several studies have indicated that these genes are controlled by a complex regulatory network, including a variety of cis-acting DNA elements and regulatory factors. Until now, however, relatively little information is available on external signals and their transmission influencing the expression of the structural genes. Here, we show that the light-dependent regulator velvet A (VeA) acts as a repressor on the penicillin biosynthesis, mainly via repression of the acvA gene. Expression of a regulatable alcAp-veA gene fusion in an A. nidulans strain carrying, in addition, acvAp-uidA and ipnAp-lacZ gene fusions indicated that under alcAp-inducing conditions, penicillin titres and expression of acvAp-uidA were drastically reduced compared with untransformed wild-type strains. The same level of repression was found irrespective of whether the alcAp-veA gene fusion was expressed in a veA1 or ΔveA background, with or without light. The expression of the ipnAp-lacZ gene fusion was only moderately affected indicating a less prominent effect. These findings were confirmed by the analysis of a regulatable niiAp-veA gene fusion. Under niiAp-inducing conditions, penicillin titres and acvAp-uidA expression were much lower than in untransformed wild-type strains.     

Morphological phylogeny of <Emphasis Type="Italic">Geusibia</Emphasis> Jordan, 1932 (Siphonaptera: Leptopsyllidae) and the host–parasite relationship with pikas

Thirteen species of fleas of the genus Geusibia Jordan, 1932 were included in a cladistic analysis based on morphological characters. The results support Geusibia as a monophyletic group within Ctenophyllus Wagner, 1927 (sensu lato) and there are five diagnostic characters that distinguish Geusibia from related genera of Ctenophyllus (s. l). There is no evidence to support a subgeneric classification. We propose that G. ochotona Zhan, Cai & Wu, 1997 and G. lacertosa(Smit, 1975) are junior synonyms of G. torosa Jordan, 1932. After a reconciliation analysis, only two co-speciation events were found in the host–parasite association between Geusibia and pikas (Ochotona:Ochotonidae: Lagomorpha). Therefore, there are no co-evolutionary relationships between them, although a high host preference of Geusibiaspp. is recorded. The distribution and host selection of Geusibia, relative to host associations, are also discussed. Although most specimens of Geusibia are found on pikas, the host is not the definitive factor in the distribution of the genus. Some environmental factors and some host behaviors also determine the presence of Geusibia. Therefore, Geusibia is defined as a host-habitat-dependent flea     

Molecular biology and systematics of an extinct Lemur:Pachylemur insignis

The systematic position of the extinctPachylemur insignis has been controversial: some authors consideredPachylemur as a lemur, whereas others viewed it closer toVarecia. Its classification in the genusLemur orVarecia thus remained an open question. DNA extraction from subfossil bones, using a non-destructive method, allowed us to obtain enough material to make a Southern blot. The hybridization ofPachylemur withEulemur fulvus, Lemur catta, andVarecia variegata highly repeated DNA probes showed that only theVarecia probe gave a positive signal on hybridization on thePachylemur blot. These results indicate thatPachylemur must be considered closer to the genusVarecia than toEulemur andLemur.     

Glucocorticoid‐inducible expression of a bacterial avirulence gene in transgenic Arabidopsis induces hypersensitive cell death

Pathogenic strains of Pseudomonas syringae pv. tomato carrying the avrRpt2 avirulence gene specifically induce a hypersensitive cell death response in Arabidopsis plants that contain the complementary RPS2 disease resistance gene. Transient expression of avrRpt2 in Arabidopsis plants having the RPS2 gene has been shown to induce hypersensitive cell death. In order to analyze the effects of conditional expression of avrRpt2 in Arabidopsis plants, transgenic lines were constructed that contained the avrRpt2 gene under the control of a tightly regulated, glucocorticoid-inducible promoter. Dexamethasone-induced expression of avrRpt2 in transgenic lines having the RPS2 gene resulted in a specific hypersensitive cell death response that resembled a Pseudomonas syringae-induced hypersensitive response and also induced the expression of a pathogenesis-related gene (PR1). Interestingly, high level expression of avrRpt2 in a mutant rps2–101C background resulted in plant stress and ultimately cell death, suggesting a possible role for avrRpt2 in Pseudomonas syringae virulence. Transgenic RPS2 and rps2 plants that contain the glucocorticoid-inducible avrRpt2 gene will provide a powerful new tool for the genetic, physiological, biochemical, and molecular dissection of an avirulence gene-specified cell death response in both resistant and susceptible plants.     

Can extreme morphology in Bosmina reduce predation risk from Leptodora? An experimental test

Bosmina (Cladocera) populations, especially within the subgenus Eubosmina, show a variety of phenotypes that exhibit large differences in body size and shape and antennule length. In some populations, the morphological traits also vary during the season, with the most extreme forms occurring in periods with high densities of certain invertebrate predators. However, while temporal phenotypic variation in other cladocerans, as in the family Daphnidae, has been shown to be an adaptation to reduce the risk of predation by invertebrate predators, the reason for such changes in Bosmina is much less clear. We examined whether certain morphological traits in Bosmina species could act as a defence against invertebrate predators. We tested three Bosmina forms (subgenus Eubosmina), differing in morphology from each other, which are found in lakes together with the predator Leptodora kindtii (Cladocera). Bosmina (E.) longispina has a relatively low and elongated carapace with a caudal mucro, and short antennule, B. (E.) coregoni gibbera has a higher and more protruding carapace without caudal mucro, and a much longer antennule. Finally, B. (E.) coregoni retro extensa has a carapace like that of B. longispina but with no caudal mucro and a much longer antennule. In one experiment, B. longispina and B. gibbera were exposed for 12 h to Leptodora in Petri dishes. In a second experiment, we observed directly the escape efficiency of B. longispina, B. gibbera and B. retro extensa, and the handling time of Leptodora. The two Bosmina forms with more extreme morphological features had a lower death rate and higher escape efficiency than B. longispina. Prey that escaped did so, in most cases, within 5 min. Predator handling time was correlated to predator body length and antennule length of the prey. The results suggests that Bosmina species with extreme morphological traits may be less vulnerable to invertebrate predators. Received: 8 June 1998 / Accepted: 5 October 1998     

Reactivation of a silenced minimal Mutator transposable element system following low-energy nitrogen ion implantation in maize

In maize, Mutator transposable elements are either active or silenced within the genome. In response to environmental stress, silenced Mutator elements could be reactivated, leading to changes in genome structure and gene function. However, there is no direct experimental evidence linking environmental stress and Mutator transposon reactivation. Using a maize line that contains a single inactive MuDR and a lone nonautonomous Mutator element, a Mu1 insertion in the recessive reporter allele a1-mum2 in an inactive Mutator background, we directly assessed Mutator reactivation following low-energy nitrogen ion implantation. We observed that N⁺ implantation decreased cytosine methylation in MuDR terminal inverted repeats and increased expression of mudrA and mudrB. Both changes were associated with increased transpositional activity of MuDR through reactivation of the inactive minimal Mutator transposable element system. This study provides direct evidence linking environmental stress agents and Mutator transposon mobilization in maize. In addition, the observed changes to DNA methylation suggest a new mechanism for mutations by low-energy ion implantation.