Organogenesis and somatic embryogenesis in Codiaeum variegatum (L.) Blume cv. “Corazón de Oro”

Summary Adventive organogenesis and somatic embryogenesis were induced from leaf explants taken from in vitro or in vivo plants of Codiaeum variegatum cv. “Corazón de Oro.” Shoot multiplication occurred with N⁶-benzyladenine (BA) alone, where the simultaneous production of adventitious buds and somatic embryos occurred at the fourth subculture, and on leaves not in contact with the medium. A medium with BA and 2,4 dichlorophenoxy acetic acid (2,4-D) produced the largest organogenic response, for both in vivo- and in vitro-produced explants. Somatic embryogenesis was only induced when such explants were transferred to a medium lacking 2,4-D. Thus, a medium with BA only produced the largest percentage of explants with shoots and embryos. Replacing BA with thidiazuron induced up to 100% bud regeneration on in vitro-produced explants by 60 d, but was slower for in vitro-grown explants. Both types of embryos exhibited growth arrest that was partially overcome by transfer to hormone-free basal medium with activated charcoal. Rooted plants from all explants were successfully obtained on a medium with indole-butyric acid (IBA).     

In vitro recurrent selection of potato: production and characterization of salt tolerant cell lines and plants

A stable salt-tolerant potato cell line, able to grow on media containing 60–450 mM NaCl (i.e. low to high salinity) was selected. Callus grown on 120 or 150 mM NaCl showed higher fresh weights than the rest of the treatments. Replacing NaCl by KCl or Na2SO4 showed that reductions in fresh weight were mainly due to the presence of Na+ ions. When PEG 6000 was added to the medium instead of salt, the salt tolerant cell lines were unable to overcome the PEG-induced water stress. Whole plants, regenerated from salt tolerant callus, exhibited salt stress tolerance as evidenced by their higher fresh and dry weights when watered with 90 mM NaCl, and they also produced more tubers per plant under salt stress. Salt-tolerant plants differed phenotypically from control plants both in terms of leaf shape, tuber flesh and skin colour, which was reddish. In addition, DNA fingerprinting by RAPDs, with 70 different primers, confirmed that the salt tolerant regenerants also differed genotypically from the control, salt sensitive Kennebec potato plants from which they had been selected. This revised version was published online in June 2006 with corrections to the Cover Date.     

Identification and characterization of an intervening sequence within the 23S ribosomal RNA genes of Campylobacter jejuni

Campylobacter jejuni is a significant cause of bacterial enteritis in humans. Three of seven C. jejuni isolates examined were found to contain fragmented 23S rRNA. The occurrence of fragmented 23S rRNA correlated with the presence of an intervening sequence (IVS) within the 23S rRNA genes. The IVS is 157 nucleotides in length and replaces an eight nucleotide sequence in the 23S rRNA genes of C. jejuni isolates that contain intact 23S rRNA. The two ends of the IVS share 31 bases of complementarity that could form a stem-loop structure. Fragmentation of the 23S ribosomal RNA results from the excision of the IVS from the transcribed RNA; the 3’ cleavage site maps within the putative stem-loop formed by the IVS. Southern hybridization analysis revealed that the IVS is not present in the genomes of isolates that contain intact 23S rRNA, suggesting that the IVS is not derived from Campylobacter chromosomal sequences. The C. jejuni IVS is located at a position analogous to that of the IVSs found in both Salmonella and Yersinia spp.     

Identification of replication-competent HSV-1 Cgal strain targets in a mouse model of human hepatocarcinoma xenograft

Recent studies based on animal models have shown the advantages and potential of oncolytic viral therapy using HSV-1 -based replication-competent vectors in the treatment of liver tumors, but little is known about the cellular targets that are modulated during viral infection. In the present work, we have studied the effects of intratumoral injections of HSV-1 Cgal⁺ strain in a murine model of human hepatoma xenografts. Viral replication was assessed for more than 1 month, leading to a significant reduction of tumor growth rate mediated, in part, by a cyclin B dependent cell proliferation arrest. Early events resulting in this effect were analyzed using a proteomic approach. Protein extracts from xenografted human hepatomas treated with saline or HSV-1 Cgal⁺ strain during 24 h were compared by 2-D DIGE and differential spots were identified by nanoLC-ESI-MS/MS. Alterations on glutathione S transferase 1 Omega, and ERp29 suggest novel HSV-1 Cgal⁺ targets in solid liver tumors. Additionally, ERp29 showed a complex differential isoform pattern upon HSV-1 Cgal⁺ infection, suggesting regulatory mechanisms based on post-translational modification events.     

Identification and characterization of a linear-plasmid-encoded factor H-binding protein (FhbA) of the relapsing fever spirochete Borrelia hermsii

In North America, tick-borne relapsing fever (TBRF) is caused by the spirochete species Borrelia hermsii, Borrelia parkeri, and Borrelia turicatae. We previously demonstrated that some isolates of B. hermsii and B. parkeri are capable of binding factor H and that cell-bound factor H can participate in the factor I-mediated cleavage of C3b. Isolates that bound factor H expressed a factor H-binding protein (FHBP) that we estimated to be approximately 19 to 20 kDa in size and thus, pending further characterization, temporarily designated FHBP19. Until this report, none of the FHBPs of the TBRF spirochetes had been characterized. Here we have recovered the gene encoding the FHBP of B. hermsii YOR from a lambda ZAP II library and determined its sequence. The gene encodes a full-length protein of 22.7 kDa, which after processing is predicted to be 20.5 kDa. This protein, which we redesignate factor H-binding protein A (FhbA), is unique to B. hermsii. Two-dimensional pulsed-field gel electrophoresis and hybridization analyses revealed that the B. hermsii gene encoding FhbA is a single genetic locus that maps to a linear plasmid of approximately 220 kb. The general properties of FhbA were also assessed. The protein was found to be surface exposed and lipidated. Analysis of the antibody response to FhbA in infected mice revealed that it is antigenic during infection, indicating expression during infection. The identification and characterization of FhbA provides further insight into the molecular mechanisms of pathogenesis of the relapsing fever spirochetes.     

Structure of factor H-binding protein B (FhbB) of the periopathogen, Treponema denticola: insights into progression of periodontal disease

Periodontitis is the most common disease of microbial etiology in humans. Periopathogen survival is dependent upon evasion of complement-mediated destruction. Treponema denticola, an important contributor to periodontitis, evades killing by the alternative complement cascade by binding factor H (FH) to its surface. Bound FH is rapidly cleaved by the T. denticola protease, dentilisin. In this report, the structure of the T. denticola FH-binding protein, FhbB, was solved to 1.7 Å resolution. FhbB possesses a unique fold that imparts high thermostability. The kinetics of the FH/FhbB interaction were assessed using surface plasmon resonance. A K_D value in the micromolar range (low affinity) was demonstrated, and rapid off kinetics were observed. Site-directed mutagenesis and sucrose octasulfate competition assays collectively indicate that the negatively charged face of FhbB binds within FH complement control protein module 7. This study provides significant new insight into the molecular basis of FH/FhbB interaction and advances our understanding of the role that T. denticola plays in the development and progression of periodontal disease.