High-sensitivity NaYF4:Yb3+/Ho3+/Tm3+ phosphors for optical temperature sensing based on thermally coupled and non-thermally coupled energy levels.

Non-contact optical temperature sensors are highly sought after by researchers due to their satisfactory temperature resolution (δ(T) < 0.1 °C), high relative thermal sensitivity (Sr > 1% °C-1), fast temporal response (t < 0.1 s), and long-term optical stability. In this study, NaYF4:Yb3+/Ho3+/Tm3+ upconversion nanoparticles were prepared by a solvothermal method, and their crystal structure, microscopic morphology, and luminescence mechanism, together with the temperature sensing properties of the specimens, were investigated. Under 980 nm laser excitation, the specimens exhibited strong upconversion luminescence, and the emission peaks corresponded to the characteristic energy level jumps of Ho3+ and Tm3+, respectively. The temperature-dependent luminescence spectra of the samples were investigated based on the fluorescence intensity ratio (FIR) technique over a temperature gradient of 295-495 K. The samples are based on thermally coupled energy levels (TCLs: 1G4(1,2) → 3H6(Tm3+)) and non-thermally coupled energy levels (NTCLs: 3F3 → 3H6(Tm3+) and 5F3 → 5I8(Ho3+), 3F3 → 3H6(Tm3+) and 1G4 → 3H6(Tm3+), 3F3 → 3H6(Tm3+) and 5F5 → 5I8(Ho3+), 3F3 → 3H6(Tm3+) and 5F4 → 5I8(Ho3+)) for temperature sensing performance. The maximum absolute sensitivity (Sa), relative sensitivity (Sr), and minimum temperature resolution δ(T) were found to be 0.0126 K-1 (495 K), 1.7966% K-1 (345 K), and 0.0167 K, respectively, which are better than those of most sensing materials, and the simultaneous action of multiple coupling energy levels can further improve the temperature precision. This study indicates that the sample has a good value for optical temperature measurement and also provides new ideas for the exploration of other high-quality optical temperature sensing materials.

Fluorescence temperature sensing of NaYF4:Yb3+/Tm3+@NaGdF4:Nd3+/Yb3+ nanoparticles at low and high temperatures.

NaYF4:Yb3+/Tm3+@NaGdF4:Nd3+/Yb3+upconversion nanoparticles were prepared using a solvothermal method, and the effects of key factors such as the content of sensitiser Nd3+and Yb3+on their luminescence properties were investigated. The nanoparticles are homogeneous in size and well dispersed. Under 808 nm excitation, it can produce strong upconversion fluorescence. At the same time, the nanoparticles have good temperature sensing properties at the thermally coupled energy levels of 700 and 646 nm for Tm3+. Using its fluorescence intensity ratio, accurate temperature measurements can be performed, and it has been found that it exhibits different temperature sensing properties in low and high-temperature regions. The maximum relative sensitivity was found to be 0.88% K-1and 1.89% K-1for the low-temperature region of 285-345 K and the high-temperature region of 345-495 K. The nanoparticles were applied to the internal temperature measurement of lithium batteries and the actual high-temperature environment, respectively, and were found to have good temperature measurement performance.

Production of Plant-Associated Volatiles by Select Model and Industrially Important Streptomyces spp.

The Streptomyces produce a great diversity of specialized metabolites, including highly volatile compounds with potential biological activities. Volatile organic compounds (VOCs) produced by nine Streptomyces spp., some of which are of industrial importance, were collected and identified using gas chromatography-mass spectrometry (GC-MS). Biosynthetic gene clusters (BGCs) present in the genomes of the respective Streptomyces spp. were also predicted to match them with the VOCs detected. Overall, 33 specific VOCs were identified, of which the production of 16 has not been previously reported in the Streptomyces. Among chemical classes, the most abundant VOCs were terpenes, which is consistent with predicted biosynthetic capabilities. In addition, 27 of the identified VOCs were plant-associated, demonstrating that some Streptomyces spp. can also produce such molecules. It is possible that some of the VOCs detected in the current study have roles in the interaction of Streptomyces with plants and other higher organisms, which might provide opportunities for their application in agriculture or industry.

Virulence mechanisms of plant-pathogenic Streptomyces species: an updated review.

Gram-positive Actinobacteria from the genus Streptomyces are best known for their morphological complexity and for their ability to produce numerous bioactive specialized metabolites with useful applications in human and veterinary medicine and in agriculture. In contrast, the ability to infect living plant tissues and to cause diseases of root and tuber crops such as potato common scab (CS) is a rare attribute among members of this genus. Research on the virulence mechanisms of plant-pathogenic Streptomyces spp. has revealed the importance of the thaxtomin phytotoxins as key pathogenicity determinants produced by several species. In addition, other phytotoxic specialized metabolites may contribute to the development or severity of disease caused by Streptomyces spp., along with the production of phytohormones and secreted proteins. A thorough understanding of the molecular mechanisms of plant pathogenicity will enable the development of better management procedures for controlling CS and other plant diseases caused by the Streptomyces.

Positive and Negative Regulation of the Virulence-Associated Coronafacoyl Phytotoxin in the Potato Common Scab Pathogen Streptomyces scabies.

The potato common scab pathogen Streptomyces scabies produces N-coronafacoyl-l-isoleucine (CFA-Ile), which is a member of the coronafacoyl family of phytotoxins that are synthesized by multiple plant pathogenic bacteria. The CFA-Ile biosynthetic gene cluster contains a regulatory gene, cfaR, which directly controls the expression of the phytotoxin structural genes. In addition, a gene designated orf1 encodes a predicted ThiF family protein and is cotranscribed with cfaR, suggesting that it also plays a role in the regulation of CFA-Ile production. In this study, we demonstrated that CfaR is an essential activator of coronafacoyl phytotoxin production, while ORF1 is dispensable for phytotoxin production and may function as a helper protein for CfaR. We also showed that CFA-Ile inhibits the ability of CfaR to bind to the promoter region driving expression of the phytotoxin biosynthetic genes and that elevated CFA-Ile production by overexpression of both cfaR and orf1 in S. scabies increases the severity of disease symptoms induced by the pathogen during colonization of potato tuber tissue. Overall, our study reveals novel insights into the regulatory mechanisms controlling CFA-Ile production in S. scabies and it provides further evidence that CFA-Ile is an important virulence factor for this organism.

The coronafacoyl phytotoxins: structure, biosynthesis, regulation and biological activities.

Phytotoxins are secondary metabolites that contribute to the development and/or severity of diseases caused by various plant pathogenic microorganisms. The coronafacoyl phytotoxins are an important family of plant toxins that are known or suspected to be produced by several phylogenetically distinct plant pathogenic bacteria, including the gammaproteobacterium Pseudomonas syringae and the actinobacterium Streptomyces scabies. At least seven different family members have been identified, of which coronatine was the first to be described and is the best-characterized. Though nonessential for disease development, coronafacoyl phytotoxins appear to enhance the severity of disease symptoms induced by pathogenic microbes during host infection. In addition, the identification of coronafacoyl phytotoxin biosynthetic genes in organisms not known to be plant pathogens suggests that these metabolites may have additional roles other than as virulence factors. This review focuses on our current understanding of the structures, biosynthesis, regulation, biological activities and evolution of coronafacoyl phytotoxins as well as the different methods that are used to detect these metabolites and the organisms that produce them.

Regulation of coronafacoyl phytotoxin production by the PAS-LuxR family regulator CfaR in the common scab pathogen Streptomyces scabies.

Potato common scab is an economically important crop disease that is characterized by the formation of superficial, raised or pitted lesions on the potato tuber surface. The most widely distributed causative agent of the disease is Streptomyces scabies, which produces the phytotoxic secondary metabolite thaxtomin A that serves as a key virulence factor for the organism. Recently, it was demonstrated that S. scabies can also produce the phytotoxic secondary metabolite coronafacoyl-L-isoleucine (CFA-L-Ile) as well as other related metabolites in minor amounts. The expression of the biosynthetic genes for CFA-L-Ile production is dependent on a PAS-LuxR family transcriptional regulator, CfaR, which is encoded within the phytotoxin biosynthetic gene cluster in S. scabies. In this study, we show that CfaR activates coronafacoyl phytotoxin production by binding to a single site located immediately upstream of the putative -35 hexanucleotide box within the promoter region for the biosynthetic genes. The binding activity of CfaR was shown to require both the LuxR and PAS domains, the latter of which is involved in protein homodimer formation. We also show that CFA-L-Ile production is greatly enhanced in S. scabies by overexpression of both cfaR and a downstream co-transcribed gene, orf1. Our results provide important insight into the regulation of coronafacoyl phytotoxin production, which is thought to contribute to the virulence phenotype of S. scabies. Furthermore, we provide evidence that CfaR is a novel member of the PAS-LuxR family of regulators, members of which are widely distributed among actinomycete bacteria.

[MEF2 and myogenesis].

Recent genetic and biochemical studies have demonstrated that skeletal muscle growth and differentiation in vertebrates are controlled by a core regulatory network which consists of two families of transcriptional factors, the MyoD group basic helix-loop-helix (bHLH) muscle regulatory factors (MRFs) and the myocyte enhancer factor 2 (MEF2) group of MADS-box regulators. During development, MEF2 interacts genetically and physically with different members of this myogenic network and together they cooperate to positively or negatively regulate transcription of downstream muscle-specific differentiation genes. This paper reviews current understanding of molecular mechanism of these interactions and essential roles that MEF2 plays in skeletal muscle growth and differentiation during development.