Genetic dissection of maize seedling root system architecture traits using an ultra-high density bin-map and a recombinant inbred line population

Maize(Zea mays) root system architecture(RSA)mediates the key functions of plant anchorage and acquisition of nutrients and water. In this study,a set of 204 recombinant inbred lines(RILs) was derived from the widely adapted Chinese hybrid ZD958(Zheng58 Chang7-2),genotyped by sequencing(GBS) and evaluated as seedlings for 24 RSA related traits divided into primary,seminal and total root classes. Signi ficant differences between the means of the parental phenotypes were detected for 18 traits,and extensive transgressive segregation in the RIL population was observed for all traits. Moderate to strong relationships among the traits were discovered. A total of 62 quantitative trait loci(QTL) were identi fied that individually explained from1.6% to 11.6%(total root dry weight/total seedling shoot dry weight) of the phenotypic variation. Eighteen,24 and 20 QTL were identi fied for primary,seminal and total root classes of traits,respectively. We found hotspots of 5,3,4 and 12 QTL in maize chromosome bins 2.06,3.02-03,9.02-04,and 9.05-06,respectively,implicating the presence of root gene clusters or pleiotropic effects. These results characterized the phenotypic variation and genetic architecture of seedling RSA in a population derived from a successful maize hybrid.     

The bacterial virulence factor NleA is required for the disruption of intestinal tight junctions by enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) is a diarrhoeal pathogen that adheres to epithelial cells of the small intestine and uses a type III secretion system to inject effector proteins into host cells. EPEC infection leads to disruption of host intestinal tight junctions that are important for maintaining intestinal barrier function. This disruption is dependent on the bacterial type III secretion system, as well as the translocated effectors EspF and Map. Here we show that a third type III translocated bacterial effector protein, NleA, is also involved in tight junction disruption during EPEC infection. Using the drug Brefeldin A, we demonstrate that the effect of NleA on tight junction integrity is related to its inhibition of host cell protein trafficking through COPII-dependent pathways. These results suggest that NleA's striking effect on virulence is mediated, at least in part, via its role in disruption of intestinal barrier function.     

Identification of a disease resistance locus in Arabidopsis that is functionally homologous to the RPG1 locus of soybean

A new disease resistance locus in Arabidopsis, RPS3 , was identified using a previously cloned avirulence gene from a non- Arabidopsis pathogen. The avrB avirulence gene from the soybean pathogen Pseudomonas syringae pv. glycinea was transferred into a P. syringae pv. tomato strain that is virulent on Arabidopsis , and conversion to avirulence was assayed on Arabidopsis plants. The avrB gene had avirulence activity on most, but not all, Arabidopsis ecotypes. Of 53 ecotypes examined, 45 were resistant to a P. syringae pv. tomato strain carrying avrB , and eight were susceptible. The inheritance of this resistance was examined using crosses between the resistant ecotype Col-0 and the susceptible ecotype Bla-2. In F₂ plants from this cross, the ratio of resistant:susceptible plants was approximately 3:1, indicating that resistance to P. syringae expressing avrB is determined by a single dominant locus in ecotype Col-0, which we have designated RPS3 . Using RFLP analysis, RPS3 was mapped to chromosome 3, adjacent to markers M583 and G4523, and ≤ 1 cM from another disease resistance locus, RPM1 . In soybean, resistance to P. syringae strains that carry avrB is controlled by the locus RPG1 . Thus, RPG1 and RPS3 both confer avrB -specific disease resistance, suggesting that these genes may be homologs.     

Stability of soluble and extracellular vesicle-associated trypsin-like protease (TLP) activity of Bacteroides gingivalis W50

Comparison was made of the specific activities of whole extracellular soluble protein (EP) and extracellular vesicle (ECV)-associated trypsin-like protease (TLP) activity from batch cultures of Bacteroides gingivalis W50. Rapid loss of activity occurred when these fractions were maintained at 37 degrees C in the presence of DTT. Residual levels of activity were detected after incubation of ECV and EP for up to 8 days under non-reducing conditions. Rates of activity loss in EP and ECV were similar. Mixtures of EP and ECV, in the same proportions as found in the culture supernatant showed neither depression nor elevation of total activity from the expected compound activities of the two separate fractions.     

U-rich tracts enhance 3' splice site recognition in plant nuclei

The process of 5' and 3' splice site definition in plant pre-mRNA splicing differs from that in mammals and yeast. In mammals, splice sites are chosen by their complementarity to U1 snRNA surrounding the /GU at the 5' splice site and by the strength of the pyrimidine tract preceding the AG/ at the 3' splice site; in plants, the 3' intron boundary is defined in a position-dependent manner relative to AU-rich elements within the intron. To determine if uridines are utilized to any extent in plant 3' splice site recognition, uridines in the region preceding the normal (−1) 3' splice site of pea rbcS3A intron 1 were replaced with adenosines. This mutant activates two cryptic 3' splice sites (+62, +95) in the downstream exon, indicating that the uridines in the region immediately preceding the normal (−1) site are essential for recognition. Placement of different length uridine tracts upstream from the cryptic +62 site indicated that a cryptic exonic 3' splice site containing 14 or 10 uridine tracts with a G at −4 can effectively outcompete the normal 3' splice site containing an eight uridine tract with a U at −4. Substitutions at the −4 position demonstrated that the identity of the nucleotide at this position greatly affects 3' splice site selection. It has been concluded that several factors affect competition between these 3' splice sites. These factors include the position of the AU transition point, the strength of the uridine tract immediately preceding the 3' terminal CAG/ and the identity of nucleotide −4.     

Role of Hpn and NixA of Helicobacter pylori in Susceptibility and Resistance to Bismuth and Other Metal Ions

Background. Helicobacter pylori produces Hpn, a 60-amino acid, histidine-rich protein that avidly binds nickel and zinc ions, and NixA, a high-affinity nickel transporter in the cytoplasmic membrane. We tested the hypothesis that Hpn and NixA govern susceptibility to metal ions in H. pylori. Materials and Methods. Hpn-negative mutants of four H. pylori strains were constructed by standard allelic exchange techniques to yield isogenic Hpn⁺/Hpn-deficient pairs. A metal concentration that inhibited growth by 50% (IC₅₀) was calculated for Ni²⁺, Zn²⁺, Cu²⁺, and Co²⁺ by comparing OD₆₀₀ of cultures in metal-supplemented and control media. Results. Among all four pairs of isogenic strains, the tolerance for Ni²⁺ was reduced significantly (p < .001) in the Hpn mutants; the mean IC₅₀ value for wild-type strains was 1.9 mM; for the mutant, it was 0.8 mM. In  contrast, growth inhibition by Zn²⁺ was identical within the fours pairs, as was Cu²⁺ and Co²⁺ tolerance in one pair tested. We also found that deletion of the hpn gene increases susceptibility to therapeutic forms of bismuth by testing a mutant and wild-type pair with ranitidine bismuth citrate, bismuth citrate, and four antibiotics. Minimal inhibitory concentrations of ranitidine bismuth citrate dropped from 9.2 to 2.3 μg/ml, and those of bismuth citrate dropped from 7.4 to 3.2 μg/ml (p < .05 for both comparisons), while susceptibility to the antibiotics was unaffected. Disruption of the nixA gene encoding the specific Ni²⁺ transport protein of H. pylori did not change susceptibility to bismuth. Conclusion. We concluded that bacteria lacking Hpn, cultured in vitro, are more susceptible than is the wild type to bismuth and Ni²⁺.     

Complexes with truncated RNAs from the large domain of Archaeoglobus fulgidus signal recognition particle

Protein SRP19 is an important component of the signal recognition particle (SRP) as it promotes assembly of protein SRP54 with SRP RNA and recognizes a tetranucleotide loop. Structural features and RNA binding activities of SRP19 of the hyperthermophilic archaeon Archaeoglobus fulgidus were investigated. An updated alignment of SRP19 sequences predicted three conserved regions and two alpha-helices. With Af-SRP RNA the Af-SRP54 protein assembled into an A. fulgidus SRP which remained intact for many hours. Stable complexes were formed between Af-SRP19 and truncated SRP RNAs, including a 36-residue fragment representing helix 6 of A. fulgidus SRP RNA.     

Binding Sites for l-[3H]Glutamate on Hippocampal Synaptic Membranes: Three Populations Differentially Affected by Chloride and Calcium Ions

The effects of Cl- and Ca2+ were studied on the specific binding of L-[3H]glutamate to multiple sites on rat hippocampal synaptic membranes. Quisqualate (5 microM) or DL-2-amino-4-phosphonobutyrate (2-APB) (300 microM) was used to discriminate two previously identified classes of binding sites. Saturation isotherms and displacement curves constructed under different ionic conditions suggested that the effects of Cl- and Ca2+ could best be explained by postulating the existence of three major binding site populations in this preparation rather than two. The binding of L-glutamate to Glu A sites exhibits an absolute dependence on Cl-, and Ca2+ markedly increases the maximum density of these sites. Glu A sites bind quisqualate and 2-APB with relatively high affinity. Cl- (47 mM) more than doubles the maximum density of Glu B sites, but Ca2+ appears to have no effect. Glu B sites can be discriminated from the other classes by their relatively low affinity for quisqualate and 2-APB. There is reason to think that the Glu B population is heterogeneous. The novel Glu C population can be virtually selectively labeled by exposing 2-APB-sensitive binding sites to radioligand in Tris-HOAc buffer with Ca2+. Binding of L-[3H]glutamate to these sites is enhanced by both Cl- and Ca2+, but requires neither ion. Ca2+ appears to increase both the affinity of Glu C sites for L-glutamate and their maximum binding site density. In the presence of Ca2+ and Cl-, Glu C sites bind the radioligand with micromolar affinity (KD approximately 2 microM) and high capacity (Bmax approximately 160 pmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)