Pyramiding Bt genes for increasing resistance of cotton to two major lepidopteran pests: Spodoptera litura and Heliothis armigera

To more effectively control two major cotton insects (cotton bollworm and Spodoptera litura) and improve the efficacy of the pest resistance management, novel transgenic plants expressing Bacillus thuringiensis Cry9C gene were generated, and gene stacking strategy was incorporated. Initially, a binary plasmid vector harboring Cry9C gene was introduced into an elite cotton cultivar Simian-3 by Agrobacterium-mediated transformation. Integration and expression of the Cry9C genes in three transgenic lines were confirmed by PCR and RT-PCR. Among these transgenic lines, T0 generation of line 16 (L-16) with normal phenotypes were selected by ELISA assays for its highest expression level of Cry9C. In T1 population of L-16, the expression level of Cry9C ranged from 29 to 45 μg/g fresh leaf. The following insect bioassays demonstrated that transgenic S3-35S::Cry9C cotton plants exhibited moderate toxicity to Heliothis armigera but strong toxicity to S. litura compared with the transgenic plants expressing Cry 1Ac gene. For incorporation of gene staking strategy, Cry9C gene and Cry 2A or Cry 1Ac were pyramided, respectively by sexual crossing. The expression of Cry9C protein in all F1 progenies had a similar level as the parent plants indicating the high heritability of Bt genes in transgenic progenies. Progenies from both Cry9C × Cry 2A and Cry9C × Cry 1Ac exhibited higher resistance to S. litura compared with their parents. Together our data demonstrated that our newly generated transgenic plants represent a reservoir of novel insect-resistant materials in cotton breeding, and the successful incorporation of gene pyramiding technology can provide a new solution of developing multiple resistance management strategies.     

Biosynthesis of Sibiromycin,a Potent Antitumor Antibiotic

Pyrrolobenzodiazepines, a class of natural products produced by actinomycetes, are sequence selective DNA alkylating compounds with significant antitumor properties. Among the pyrrolo[1,4]benzodiazepines (PBDs) sibiromycin, one of two identified glycosylated PBDs, displays the highest affinity for DNA and the most potent antitumor properties. Despite the promising antitumor properties clinical trials of sibiromycin were precluded by the cardiotoxicity effect in animals attributed to the presence of the C-9 hydroxyl group. As a first step toward the development of sibiromycin analogs, we have cloned and localized the sibiromycin gene cluster to a 32.7-kb contiguous DNA region. Cluster boundaries tentatively assigned by comparative genomics were verified by gene replacement experiments. The sibiromycin gene cluster consisting of 26 open reading frames reveals a “modular” strategy in which the synthesis of the anthranilic and dihydropyrrole moieties is completed before assembly by the nonribosomal peptide synthetase enzymes. In addition, the gene cluster identified includes open reading frames encoding enzymes involved in sibirosamine biosynthesis, as well as regulatory and resistance proteins. Gene replacement and chemical complementation studies are reported to support the proposed biosynthetic pathway.Pyrrolo[1,4]benzodiazepines (PBDs) are a class of natural products found in actinomycetes (Fig. ​(Fig.1)1) and defined by a common pyrrolo[1,4]benzodiazepine ring system (41). They are sequence-selective DNA alkylating agents with significant antitumor properties (21). Once in the minor groove of DNA an aminal bond is formed between the electrophilic C-11 of a PBD and the exocyclic N-2 of a guanine base in a double-stranded DNA (20). Formation of the PBD-DNA complex causes very little distortion of the double-helical structure of DNA (20), and as such this complex is less readily repaired by DNA repair proteins compared to DNA adducts with other alkylating agents (4), significantly contributing to the potency of PBDs. Successful syntheses of PBD analogs have been reported, but synthetic procedures for the more chemically diverse PBDs are laborious and have modest yields (1, 44). In addition, a chemical synthesis for glycosylated PBDs has not yet been accomplished. Structure-activity relationship studies on the synthetically and naturally produced PBDs showed that the C-9 hydroxylation present in anthramycin is the source of the cardiotoxic properties of this compound (Fig. ​(Fig.1)1) (3, 17, 26, 38). These studies also showed that O glycosylation at C7 significantly enhanced DNA-binding affinity (Fig. ​(Fig.1)1) (17). The only known glycosylated PBDs are sibiromycin and sibanomicin produced by Streptosporangium sibiricum and Micromonospora sp., respectively, both containing a sibirosamine moiety (16, 35). Only the producer of sibiromycin is commercially available. A loose correlation between DNA binding affinity and cytotoxicity has been shown with naturally and synthetically produced PBDs (42). Sibiromycin has the highest DNA binding affinity and cytotoxicity with 50% inhibitory concentrations varying from 4 to 1.7 pM in leukemia, plasmacytoma, and ovarian cancer cell lines (42). Despite its potency, further testing of sibiromycin is precluded due to the presence of C-9 hydroxyl group responsible for the cardiotoxic properties. In order to generate analogs of glycosylated PBDs by combinatorial biosynthesis and to exploit their potency, we chose to characterize the sibiromycin gene cluster.Open in a separate windowFIG. 1.(A) Pyrrolobenzodiazepine common ring system. (B) Metabolic precursors and chemical structures of sibiromycin, anthramycin, tomaymycin, and lincomycin A.The metabolic precursors of the pyrrolobenzodiazepine ring of three PBDs (anthramycin, sibiromycin, and tomaymycin) were identified by feeding experiments to be l-tryptophan via the kynurenine pathway for the anthranilate moiety and l-tyrosine for the hydropyrrole moiety (11), suggesting a common biosynthetic pathway for these moieties in PBDs. The tyrosine-to-hydropyrrole transformation has been also identified by feeding studies in the biosynthesis of lincomycin, a lincosamide antibiotic (2) (Fig. ​(Fig.1B).1B). Despite the sequencing of the biosynthetic gene clusters of anthramycin (10) and lincomycin (37), limited functional assignment of open reading frames (ORFs) and elucidation of the biosynthetic pathways were reported partly due to the presence of several gene products with no significant similarities to functionally characterized enzymes. We reasoned that we could take advantage of the identification of the sibiromycin gene cluster not only to try to lay the groundwork for the production of analogs of sibiromycin by combinatorial biosynthesis but also to establish the biosynthetic pathways of the anthranilate and the hydropyrrole moieties by a comparative analysis of the PBDs and lincomycin gene clusters. To help in this analysis, we have also utilized the gene cluster of another PBD, tomaymycin, whose characterization is reported in the accompanying study (24a). The comparative analysis takes advantage of the presence of similarity and differences at the anthranilate and hydropyrrole moieties among these natural products (Fig. ​(Fig.1).1). For example, both anthramycin and sibiromycin contain C-8 methyl and C-9 hydroxyl substituents not present in tomaymycin. However, tomaymycin shares with sibiromycin a C-7 hydroxyl substituent. Therefore, homologous proteins involved in C-9 hydroxylation are expected to be present in the anthramycin and sibiromycin gene cluster but absent in the tomaymycin gene cluster. We applied a similar approach for the biosynthesis of the hydropyrrole moiety using also the lincomycin gene cluster.In the present study, we describe the cloning and sequencing of the sibiromycin gene cluster, the first biosynthetic gene cluster for a glycosylated PBD. Gene replacement experiments were used to confirm that the identified gene cluster was involved in sibiromycin biosynthesis, to define the boundaries of the sibiromycin gene cluster, and to elucidate the biosynthesis of the anthranilate moiety. Using the comparative approach, we were able not only to elucidate the sibiromycin biosynthetic pathway with a certain degree of confidence but also to assign ORFs in the anthramycin gene cluster contributing to the determination of the anthramycin biosynthetic pathway. The proposed biosynthetic pathway for the anthranilic moiety was supported by gene replacement and chemical complementation studies. The data reported here provide the basis for future studies on the enzymes involved in the biochemistry present in these pathways and for combinatorial biosynthetic experiments for the production of glycosylated PBDs.     

Molecular charcterization of tatD DNAse gene from Ralstonia paucula RA4T soil bacterium

Ralstonia paucula strain RA4^T, a gram negative, non-spore forming, motile bacterium having positive catalase and oxidase test, was isolated from surface soil. Twin arginine translocation protein type D (TatD) is shown to be located in cytoplasm and exhibits magnesium-dependent DNase. A tatD DNase gene was isolated and cloned from Ralstonia paucula RA4^T genome. Nucleotide sequence analysis of the gene revealed 813 nucleotides encoding a protein of 270 amino acid residues. The tatD gene showed a high similarity to homolog gene from Ralstonia pickettii strain 12D. The deduced polypeptide sequence of TatD DNase from R. paucula RA4^T had a typical catalytic site, HHPLDEHRHDP, and its calculated molecular mass and predicted isoelectric point were 29616 Da and 5.33, respectively. The deduced amino acid sequence showed a high degree of similarity to TatD DNase isoforms from Ralstonia genus and other sources. Predicted three-dimensional structure of TatD confirmed the presence of active site and theoretical function as DNase.     

NDRG1 expression is related to the progression and prognosis of gastric cancer patients through modulating proliferation,invasion and cell cycle of gastric cancer cells

N-myc downstream-regulated gene 1 (NDRG1) has been proposed as a tumor suppressor gene in many different types of tumors, but its potential function and corresponding mechanism are not yet fully elucidated. This study aims to detect the possible function of NDRG1 in gastric cancer progression. In this study, 112 paired gastric cancer tissues and corresponding nonmalignant gastric tissues were utilized to identify the differential protein expression of NDRG1 by immunohistochemistry and its clinical significance was analyzed. Furthermore, 49 of 112 paired gastric specimens were used to detect the differential mRNA expression by real-time PCR. The over expression of NDRG1 in human gastric cancer cell line AGS by PcDNA3.1–NDRG1 transfection was utilized to detect the role of NDRG1 in regulating the biological behavior of gastric cancer. NDRG1 expression was significantly decreased in primary gastric cancer tissues, compared with its corresponding nonmalignant gastric tissues (p < 0.05), and its decreased expression was significantly associated with lymph node metastasis (p < 0.01), invasion depth (p < 0.01) and differentiation (p < 0.05). Additionally, the overall survival rate of gastric cancer patients with high expression of NDRG1 was higher than those with low expression during the follow-up period. NDRG1 overexpression suppressed cells proliferation, invasion and induced a G1 cell cycle arrest in gastric cancer. Furthermore, the down-regulation of NDRG1 in gastric cancer metastatic progression was correlated to E-cadherin and MMP-9. Our results verify that NDRG1 acts as a tumor suppressor gene and may play an important role in the metastasis progression and prognosis of gastric cancer.     

Microporation is an efficient method for siRNA-induced knockdown of PEX5 in HepG2 cells: evaluation of the transfection efficiency,the PEX5 mRNA and protein levels and induction of peroxisomal deficiency

The pathomechanism of peroxisomal biogenesis disorders (PBDs), a group of inherited autosomal recessive diseases with mutations of peroxin (PEX) genes, is not yet fully understood. Therefore, several knockout models, e.g., the PEX5 knockout mouse, have been generated exhibiting a complete loss of peroxisomal function. In this study, we wanted to knockdown PEX5 using the siRNA technology (1) to mimic milder forms of PBDs in which the mutated peroxin has some residual function and (2) to analyze the cellular consequences of a reduction of the PEX5 protein without adaption during the development as it is the case in a knockout animal. First, we tried to optimize the transfection of the hepatoma cell line HepG2 with PEX5 siRNA using different commercially available liposomal and non-liposomal transfection reagents (Lipofectamine^® 2000, FuGENE 6, HiPerFect^®, INTERFERin?, RiboJuice?) as well as microporation using the Neon? Transfection system. Microporation was found to be superior to the transfection reagents with respect to the transfection efficiency (100 vs. 0–70 %), to the reduction of PEX5 mRNA (by 90 vs. 0–50 %) and PEX5 protein levels (by 70 vs. 0–50 %). Interestingly, we detected that a part of the cleaved PEX5 mRNA still existed as 3′ fragment (15 %) 24 h after microporation. Using microporation, we further analyzed whether the reduced PEX5 protein level impaired peroxisomal function. We indeed detected a reduced targeting of SKL-tagged proteins into peroxisomes as well as an increased oxidative stress as found in PBD patients and respective knockout mouse models. Knockdown of the PEX5 protein and functional consequences were at a maximum 48 h after microporation. Thereafter, the PEX5 protein was resynthesized, which may allow the temporal analysis of the loss as well as the reconstitution of peroxisomes in the future. In conclusion, we propose microporation as an efficient and reproducible method to transfect HepG2 cells with PEX5 siRNA. We succeeded to transiently knockdown PEX5 mRNA and its protein level leading to functional consequences similar as observed in peroxisome deficiencies.     

Expression of GroES TB antigen in tobacco and potato

As the world races towards a plant-based bioeconomy, plants known to be ideal and economical bioreactors are being harnessed for the production of recombinant proteins. The major immunodominant 10 kDa GroES TB antigen (Chaperonin 10) gene from Mycobacterium tuberculosis was selected for expression in plants as a putative tuberculosis (TB) subunit vaccine candidate. Two crops, tobacco and potato, were engineered by stable plant transformation for expression of the 10 kDa GroES TB antigen using non-viral binary vectors. The integration of the GroES TB gene into the genomes of tobacco and potato was confirmed by PCR and Southern blotting. The expression of the GroES TB antigen in tobacco was 0.04–1.2 % of the total soluble protein (TSP). However, the expression of the same TB antigen in the Indian potato cv. Kufri bahar was comparatively low (0.033 % of TSP). The recombinant GroES plant derived protein was characterised and confirmed by MALDI-TOF–TOF and ELISA. This is the first report of the expression of the 10 kDa chaperonin in tobacco and potato.     

The evolutionary pattern of aromatic amino acid biosynthesis and the emerging phylogeny of pseudomonad bacteria

Pseudomonad bacterial are a phylogenetically diverse assemblage of species named within contemporary genera that includePseudomonas, Xanthomonas andAlcaligenes. Thus far, five distinct rRNA homology groups (Groups I through V) have been established by oligonucleotide cataloging and by rRNA/DNA hybridization. A pattern of enzymic features of aromatic amino acid biosynthesis (enzymological patterning) is conserved at the level of rRNA homology, five distinct and unambiguous patterns therefore existing in correspondence with the rRNA homology groups. We sorted 87 pseudomonad strains into Groups (and Subgroups) by aromatic pathway patterning. The reliability of this methodology was tested in a blind study using coded cultures of diverse pseudomonad organisms provided by American Type Culture Collection. Fourteen of 14 correct assignments were made at the Group level (the level of rRNA homology), and 12 of 14 correct assignments were made at the finer-tuned Subgroup levels. Many strains of unknown rRNA-homology affiliation had been placed into tentative rRNA groupings based upon enzymological patterning. Positive confirmation of such strains as members of the predicted rRNA homology groups was demonstrated by DNA/rRNA hybridization in nearly every case. It seems clear that the combination of these molecular approaches will make it feasible to deduce the evolution of biochemical-pathway construction and regulation in parallel with the emerging phylogenies of microbes housing these pathways.     

Effect of polymorphisms in the CSN3 (κ-casein) gene on milk production traits in Chinese Holstein Cattle

This study was designed to evaluate significant associations between single nucleotide polymorphisms (SNPs) and milk composition and milk production traits in Chinese Holstein cows. Six SNPs were identified in the κ-casein gene using pooled DNA sequencing. The identified SNPs were genotyped by Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) methods from 507 individuals. Out of six, we identified three non-synonymous SNPs (g.10888T>C, g.10924C>A and g.10944A>G) that changed in the protein product. SIFT (Sorting_Intolerant_From_Tolerant) prediction score (0.01) demonstrated that protein changed Isoleucine > Threonine (g.10888T>C) will affect the phenotypes. Significant associations between identified SNPs and three yield traits (milk, protein and fat) and two composition traits (fat and protein percentages) were found whereas it did not reach significance for fat percentage in haplotypes association. Importantly, the significant SNPs in our results showed a large proportion of the phenotypic variation of milk protein yield and concentration. Our results suggest that CSN3 is an important candidate gene that influences milk production traits, and identified polymorphisms and haplotypes could be used as a genetic marker in programs of marker-assisted selection for the genetic improvement of milk production traits in dairy cattle.     

Progression of O6-methylguanine-DNA methyltransferase and temozolomide resistance in cancer research

Temozolomide (TMZ) is an alkylating agent that is widely used in chemotherapy for cancer. A key mechanism of resistance to TMZ is the overexpression of O⁶-methylguanine-DNA methyltransferase (MGMT). MGMT specifically repairs the DNA O⁶-methylation damage induced by TMZ and irreversibly inactivates TMZ. Regulation of MGMT expression and research regarding the mechanism of TMZ resistance will help rationalize the clinical use of TMZ. In this review, we provide an overview of recent advances in the field, with particular emphasis on MGMT structure, function, expression regulation, and the association between MGMT and resistance to TMZ.