Autophagy receptor OsNBR1 modulates salt stress tolerance in rice.

KEY MESSAGE: Autophagy receptor OsNBR1 modulates salt stress tolerance by affecting ROS accumulation in rice. The NBR1 (next to BRCA1 gene 1), as important selective receptors, whose functions have been reported in animals and plants. Although the function of NBR1 responses to abiotic stress has mostly been investigated in Arabidopsis thaliana, the role of NBR1 under salt stress conditions remains unclear in rice (Oryza sativa). In this study, by screening the previously generated activation-tagged line, we identified a mutant, activation tagging 10 (AC10), which exhibited salt stress-sensitive phenotypes. TAIL-PCR (thermal asymmetric interlaced PCR) showed that the AC10 line carried a loss-of-function mutation in the OsNBR1 gene. OsNBR1 was found to be a positive regulator of salt stress tolerance and was localized in aggregates. A loss-of-function mutation in OsNBR1 increased salt stress sensitivity, whereas overexpression of OsNBR1 enhanced salt stress resistance. The osnbr1 mutants showed higher ROS (reactive oxygen species) production, whereas the OsNBR1 overexpression (OsNBR1OE) lines showed lower ROS production, than Kitaake plants under normal and salt stress conditions. Furthermore, RNA-seq analysis revealed that expression of OsRBOH9 (respiratory burst oxidase homologue) was increased in osnbr1 mutants, resulting in increased ROS accumulation in osnbr1 mutants. Together our results established that OsNBR1 responds to salt stress by influencing accumulation of ROS rather than by regulating transport of Na+ and K+ in rice.

Decoding river pollution trends and their landscape determinants in an ecologically fragile karst basin using a machine learning model.

Karst watersheds accommodate high landscape complexity and are influenced by both human-induced and natural activity, which affects the formation and process of runoff, sediment connectivity and contaminant transport and alters natural hydrological and nutrient cycling. However, physical monitoring stations are costly and labor-intensive, which has confined the assessment of water quality impairments on spatial scale. The geographical characteristics of catchments are potential influencing factors of water quality, often overlooked in previous studies of highly heterogeneous karst landscape. To solve this problem, we developed a machining learning method and applied Extreme Gradient Boosting (XGBoost) to predict the spatial distribution of water quality in the world's most ecologically fragile karst watershed. We used the Shapley Addition interpretation (SHAP) to explain the potential determinants. Before this process, we first used the water quality damage index (WQI-DET) to evaluate the water quality impairment status and determined that CODMn, TN and TP were causing river water quality impairments in the WRB. Second, we selected 46 watershed features based on the three key processes (sources-mobilization-transport) which affect the temporal and spatial variation of river pollutants to predict water quality in unmonitored reaches and decipher the potential determinants of river impairments. The predicting range of CODMn spanned from 1.39 mg/L to 17.40 mg/L. The predictions of TP and TN ranged from 0.02 to 1.31 mg/L and 0.25-5.72 mg/L, respectively. In general, the XGBoost model performs well in predicting the concentration of water quality in the WRB. SHAP explained that pollutant levels may be driven by three factors: anthropogenic sources (agricultural pollution inputs), fragile soils (low organic carbon content and high soil permeability to water flow), and pollutant transport mechanisms (TWI, carbonate rocks). Our study provides key data to support decision-making for water quality restoration projects in the WRB and information to help bridge the science:policy gap.

Rice plastidial NAD-dependent malate dehydrogenase 1 negatively regulates salt stress response by reducing the vitamin B6 content.

Salinity is an important environmental factor that adversely impacts crop growth and productivity. Malate dehydrogenases (MDHs) catalyse the reversible interconversion of malate and oxaloacetate using NAD(H)/NADP(H) as a cofactor and regulate plant development and abiotic stress tolerance. Vitamin B6 functions as an essential cofactor in enzymatic reactions involved in numerous cellular processes. However, the role of plastidial MDH in rice (Oryza sativa) in salt stress response by altering vitamin B6 content remains unknown. In this study, we identified a new loss-of-function osmdh1 mutant displaying salt stress-tolerant phenotype. The OsMDH1 was expressed in different tissues of rice plants including leaf, leaf sheath, panicle, glume, bud, root and stem and was induced in the presence of NaCl. Transient expression of OsMDH1-GFP in rice protoplasts showed that OsMDH1 localizes to chloroplast. Transgenic rice plants overexpressing OsMDH1 (OsMDH1OX) displayed a salt stress-sensitive phenotype. Liquid chromatography-mass spectrometry (LC-MS) metabolic profiling revealed that the amount of pyridoxine was significantly reduced in OsMDH1OX lines compared with the NIP plants. Moreover, the pyridoxine content was higher in the osmdh1 mutant and lower in OsMDH1OX plants than in the NIP plants under the salt stress, indicating that OsMDH1 negatively regulates salt stress-induced pyridoxine accumulation. Furthermore, genome-wide RNA-sequencing (RNA-seq) analysis indicated that ectopic expression of OsMDH1 altered the expression level of genes encoding key enzymes of the vitamin B6 biosynthesis pathway, possibly reducing the level of pyridoxine. Together, our results establish a novel, negative regulatory role of OsMDH1 in salt stress tolerance by affecting vitamin B6 content of rice tissues.

Evolution of optical properties and electronic structures: band gaps and critical points in MgxZn1-xO (0 ≤ x ≤ 0.2) thin films.

MgxZn1-xO (ZMO) thin films with tunable Mg content were deposited by atomic layer deposition (ALD) on silicon substrates at 190 °C. The elemental and structural properties were acquired by X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy and X-ray diffraction. Spectroscopic ellipsometry measurements were performed to reveal the evolution of the dielectric functions and critical points in the ZMO thin films by point-by-point fit in the photon energy range of 1.2-6.0 eV. The dependence of the dielectric functions on doping content is clearly demonstrated and physically explained. The critical point energies and the types of interband optical transitions were extracted from standard lineshape analysis of the second derivatives of the dielectric functions. The critical point features were discussed in terms of band structure modification and structural homogeneity arisen by introducing the Mg dopant into the films. Controlling these transitions by changing the doping content will be of practical significance in emerging ZMO-based thin-film photonic and optoelectronic devices.

Optical Constants and Band Gap Evolution with Phase Transition in Sub-20-nm-Thick TiO2 Films Prepared by ALD.

Titanium dioxide (TiO2) ultrathin films with different thicknesses below 20 nm were grown by atomic layer deposition (ALD) on silicon substrates at 300 °C. Spectroscopic ellipsometry (SE) measurements were operated to investigate the effect of thickness on the optical properties of ultrathin films in the spectra range from 200 to 1000 nm with Forouhi-Bloomer (F-B) dispersion relation. It has been found that the refractive index and extinction coefficient of the investigated TiO2 ultrathin film increase while the band gap of TiO2 ultrathin film decreases monotonically with an increase in film thickness. Furthermore, with the purpose of studying the temperature dependence of optical properties of TiO2 ultrathin film, the samples were annealed at temperature from 400 to 900 °C in N2 atmosphere. The crystalline structure of deposited and annealed films was deduced by SE and supported by X-ray diffraction (XRD). It was revealed that the anatase TiO2 film started to transform into rutile phase when the annealing temperature was up to 800 °C. In this paper, a constructive and effective method of monitoring the phase transition in ultrathin films by SE has been proposed when the phase transition is not so obvious analyzed by XRD.

Prevalence of qnr determinants among extended-spectrum beta-lactamase-positive Enterobacteriaceae clinical isolates in southern Stockholm, Sweden.

Three hundred and nineteen extended-spectrum beta-lactamase-positive Enterobacteriaceae clinical isolates were screened for qnr genes. Twelve isolates were positive for qnr, including one qnrA1, two qnrB1, three qnrB2, one qnrB4, one qnrB6 and four qnrS1. No qnr-positive strains were identified among the isolates recovered before 2006. The first qnr-positive Escherichia coli was detected from a patient in 2006. qnr genes remained rare in E. coli (6/288; 2.1%), but appeared to be more prevalent in Klebsiella pneumoniae (4/25; 16%) and Enterobacter cloacae (2/3; 66.7%). All qnr-positive isolates were resistant to nalidixic acid while presenting varied susceptibilities to fluoroquinolones. Isolates harbouring qnrB4 or qnrB6 were highly resistant to all the fluoroquinolones tested. Their high-level resistance is associated with multiple chromosomal substitutions in gyrA and parC. Alterations at codons Ser-83 and Asp-87 in GyrA and at codons Ser-80 and Glu-84 in ParC were observed in these isolates.