A solvent-controlled switchable C-H alkenylation of 4-aryl-1H-pyrrole-3-carboxylates via a Pd(OAc)2 catalyzed oxidative Heck reaction was first realized. The corresponding C2 and C5 alkenylation products were obtained in good yields with high regioselectivities, respectively. The selective C5-alkenylation was successfully applied to the total synthesis of (±)-rhazinilam.
A 1,6‐addition arylation reaction of para‐quinone methides with α‐isocyanoacetamides and electron‐rich aromatic compounds under metal‐free conditions has been developed. BF3·Et2O plays two roles in the reaction: catalyzing the cyclization of α‐isocyanoacetamides to give oxazoles, and activating the para‐quinone methides to achieve the 1,6‐addition arylation process. The reaction shows good functional group tolerance, scalability, and regioselectivity. It is a consice protocol for the synthesis of diverse unsymmetrical triarylmethanes. Further transformation of the resulting triarylmethanes provides an efficient route to some functionalized molecules.
Sunflower Verticillium wilt is a widespread and destructive disease caused by the soilborne pathogen Verticillium dahliae. To better understand the process of infection and seed transmission of the fungus, sunflower roots were inoculated with a V. dahliae strain (VdBM9-6) labeled with green fluorescent protein (GFP) and monitored microscopically. After 24 to 96 h postinoculation (hpi), conidia germinated and developed into mycelium on root hairs, elongation zones, and caps of lateral roots. Mycelium colonized vascular bundles of lateral roots and taproots at 7 days postinoculation (dpi). At 10 weeks postinoculation (wpi), the epidermal cells, cortical tissues, and vascular elements of stem, petiole, and leaf veins were colonized by mycelium. By 12 wpi, strong GFP signals were detected not only on different tissues of inflorescence but also on testa of seed and a small fraction of pollen grains. A GFP signal was not observed on cotyledon tissues in the seed. Additionally, the colonization of V. dahliae on testa was also confirmed with MNP-10 selection medium, indicating that the testa of seed is the main carrier for the long distance transmission of sunflower yellow wilt.
Antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) produced by Pseudo11Wnas jl.uorescens CPF-IO and 2P24 is a principal factor enabling bacteria to suppress plant diseases caused by soilborne pathogens. In this study, a 2,4-DAPG biosynthesis locus phlACBDE cloned from strain CPF-IO was assembled into a mini-Tn5 transposon and introduced into the chromosome of P. jl.uorescens P32 (2,4-DAPG), CPF-IO and 2P24 to construct the 2,4-DAPG overproducing derivatives P32-38, CPFlO-9 and 2P24-48, respectively. All the transgenic strains showed an enhanced antibiosis capacity against plant microbial pathogens in vitro and two strains, P32-38 and CPFlO-9, provided significantly better protection against wheat take-all disease caused by Gaeumannomyces graminis var. tritici and tomato bacterial wilt caused by Ralstonia solanacearum in greenhouse. Compared to their parental strains, the 2,4-DAPG overproducing derivatives colonized to the same extent on the wheat tips in the autoclaved soil, but developed larger populations in natural soil. These results indicated that production of antibiotics 2,4-DAPG by biological control pseudomonads can contribute not only to their disease suppression capacities but also to the ecological competence in the resident microflora. Our research also suggests that it is a realistic approach to improve biocontrol capacity of P. fluorescens through the genetic modification of its antibiotic 2,4-DAPG production.
Seed-borne fungi in 69 sunflower cultivars were evaluated which comprised 52 confectionery and 17 oilseed types. Seed coats were placed on both NP-10 (Nonylphenol Ethoxylate based surfacant −10) and potato dextrose agar (PDA) media to culture fungi. The rate of contamination among the different varieties was calculated by counting seed coats with fungal colonies. The rate of contamination in the confectionary group (88%) was significantly (p ≤ 0.05) higher than in the oilseed group (71%). Of the 52 confectionery varieties, the dominant fungi recovered were Verticillium dahliae along with Alternaria spp., Fusarium spp., and Rhizopus spp., whereas the oilseed type varieties were contaminated with only V. dahliae. Molecular identification of fungal species via BLAST (Basic Alignment Search Tool) was performed on fungal sequences obtained from PCR (Polymerase Chain Reaction) analysis. The results included five Alternaria spp. that included Alternaria tenuissima, Alternaria alternata, Alternaria helianthiinficiens, Alternaria longipes, and Alternaria tamaricis, three Fusarium spp. such as Fusarium oxysporum, Fusarium incarnatum, and Fusarium proliferatum, and V. dahliae and Cladosporium cladosporioides. These were identified from pure fungal cultures recovered from seed coats. To efficiently control seed-borne fungi, four broad spectrum fungicides (carbendazim, triadimefon, caprio F-500, and flusilazole) were screened against V. dahliae isolate Gn3, which was isolated from a diseased LD 5009 sunflower plant. Flusilazole was selected based on its low half-maximal effective concentration value (EC50), 78.7 µg/mL. Seeds of diseased LD 5009 plants obtained from two different locations treated with formulated flusilazole fungicide at optimum parameters showed a significant (p ≤ 0.05) increase in seed germination and a decrease in contamination rate from 98% to less than 10%. The results affirmed that confectionery cultivars are much more susceptible to fungal contamination than oilseeds, and also that seed pretreatment is a suitable way to prevent the spread of soil- and seed-borne fungi in sunflower production.
Pseudomonas fluorescens 2P24 is an effective biological control agent of a number of soilborne plant diseases caused by pathogenic microorganisms. Among a range of secondary metabolites produced by strain 2P24, the antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) is the major determinant of its disease-suppressive capacity. In this study, we performed random mutagenesis using mini-Tn5 in order to screen for the transcriptional regulators of the phlA gene, a biosynthase gene responsible for 2,4-DAPG production. The mutant PMphlA23 with significantly decreased phlA gene expression was identified from approximately 10,000 insertion colonies. The protein sequence of the interrupted gene has 84% identity to Hfq, a key regulator important for stress resistance and virulence in Pseudomonas aeruginosa. Genetic inactivation of hfq resulted in decreased expression of phlA and reduced production of 2,4-DAPG. Furthermore, the hfq gene was also required for the expression of pcoI, a synthase gene for the LuxI-type quorum-sensing signaling molecule N-acyl-homoserine lactone. Additionally, the hfq mutation drastically reduced biofilm formation and impaired the colonization ability of strain 2P24 on wheat rhizospheres. Based on these results, we propose that Hfq functions as an important regulatory element in the complex network controlling environmental adaption in P. fluorescens 2P24.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.