Whirly1 enhances tolerance to chilling stress in tomato via protection of photosystem II and regulation of starch degradation

In plants, the chilling response involves decreased photosynthetic capacity and increased starch accumulation in chloroplasts. However, the mechanisms that modulate these processes remain unclear. We found that the SlWHY1 gene is significantly induced by chilling stress (4°C) in tomato. Three SlWHY1 overexpression (OE) lines grew better than the wild type (WT) under chilling stress; the OE plants retained intact photosynthetic grana lamellae and showed enhanced hydrolysis of starch. By contrast, RNAi lines that inhibited SlWHY1 were more affected than the corresponding WT cultivar. Their grana lamellae were damaged and starch content increased. The psbA gene encodes the key photosystem II (PSII) protein D1. We show that SlWHY1 binds to the upstream region (A/GTTACCCT/A) of SlpsbA and enhances the de novo synthesis of D1 in chloroplasts. Additionally, SlWHY1 regulates the expression of the starch-degrading enzyme α-amylase (SlAMY3-L) and the starch synthesis-related enzyme isoamylase gene (SlISA2) in the nucleus, thus modulating the starch content in chloroplasts. We demonstrate that SlWHY1 enhances the resistance of tomato to chilling stress by maintaining the function of PSII and degrading starch. Thus, overexpression of WHY1 may be an effective strategy for enhancing resistance to chilling stress of chilling-sensitive crops in agricultural production.

Enhanced biomass and lipid accumulation of mixotrophic microalgae by using low-strength ultrasonic stimulation

Ultrasonic treatment was applied to enhance the biomass and lipid accumulation of mixotrophic microalgae. The optimal microalgal ultrasonic power, ultrasonic frequency, ultrasonic interval and growth phase were 20 W, 20 Hz, 2 s and logarithmic phase, respectively. The maximum biomass concentration and lipid content reached 2.78 g L^-1 and 28.5%, which were 26.9% and 37% higher than those of the control group. Microscope analysis shows that ultrasonic exposure caused tiny cracks or holes on the surface of cell walls, but did not damage the integrity of algal cell structure. After ultrasonic stimulation, the permeability of membrane and the transport of nutrients were improved, and the utilization rate of substrate and pigment concentration increased 22.7% and 18.4%, respectively. However, excessive ultrasonic irradiation significantly inhibited the cell growth and lipid accumulation of microalgae. This study indicates the feasibility and efficiency of using low-strength ultrasound in promoting biomass and lipid production of microalgae.

Molecular mechanisms of azole resistance in Candida tropicalis isolates causing invasive candidiasis in China

OBJECTIVE

We investigated molecular mechanisms responsible for azole resistance in Candida tropicalis isolates.

METHODS

We studied 507 C. tropicalis isolates causing invasive candidiasis from ten hospitals over 5 years. Antifungal susceptibility was determined by broth microdilution methods. Point mutations in the C. tropicalis ERG11 gene that may confer azole resistance were explored and verified. The expression levels of ERG11, CYTb, MDR1 and CDR1 genes were compared in 20 fluconazole-susceptible and 20 fluconazole-resistant isolates.

RESULTS

Fluconazole-susceptible, -susceptible dose-dependent and -resistant strains accounted for 76.7% (389/507), 10.5% (53/507) and 12.8% (65/507) of C. tropicalis isolates, respectively. The ERG11 mutation A395T/W occurred in 10.7% (54/507) of isolates, all of which were resistant to fluconazole. The nucleotide mutation C461T/Y was the second most common (50/507 isolates, 9.9%), and all isolates carrying C461T/Y also had the mutation A395T/W. However, the presence of C461T did not contribute to the azole-resistant phenotype. Substitutions V125A, Y257H and G464S (<2% of isolates), which were reported for the first time in C. tropicalis, also conferred fluconazole non-susceptible phenotypes. Compared with fluconazole susceptible isolates, fluconazole-resistant isolates had higher ERG11 (fold expression level 1.42 versus 0.79, p < 0.01) but lower CYTb (fold expression level 1.26 versus 2.67, p < 0.01) gene expression levels. Three azole-resistant isolates carrying the wild-type ERG11 gene had higher levels of CDR1 and MDR1 expression.

CONCLUSIONS

ERG11 missense mutations were the major mechanism responsible for azole resistance in C. tropicalis isolates, but overexpression of ERG11, CDR1 and MDR1, as well as reduced expression of CYTb, also contributed to resistance.

Trends in atmospheric particles and their light extinction performance between 1980 and 2015 in Beijing, China

This study explored the interdecadal variations and their horizontal and vertical light extinction performances of atmospheric particulate matter with aerodynamic diameters ≤2.5 μm (PM_2.5), particulate matter with aerodynamic diameters ≤ 10 μm (PM₁₀), and total suspended particulates (TSPs) in Beijing from 1980 to 2015, using data available from historical publications. Prominent declines of PM_2.5, PM₁₀, and TSPs were detected with long-term linear trends of -6.7, -4.3, and -1.9 μg m^-3 yr^-1, respectively. Generally, on the annual scale during the studied period, it was found that PM_2.5 displayed negative correlation (R² = 0.38, p < 0.01) with visibility and positive correlation (R² = 0.41, p < 0.01) with aerosol optical depth (AOD). Comparably, PM₁₀ exhibited robust negative correlation (R² = 0.61, p < 0.01) with visibility and positive correlation (R² = 0.82, p < 0.01) with AOD. The complicated interdecadal variations and light extinction performances of PM_2.5 were found, suggesting the changes on particle composition and vertical distribution of PM_2.5 in the atmosphere.

Copper removal and microbial community analysis in single-chamber microbial fuel cell

In this study, copper removal and electricity generation were investigated in a single-chamber microbial fuel cell (MFC). Result showed that copper was efficiently removed in the membrane-less MFC with removal efficiency of 98.3% at the tolerable Cu²⁺ concentration of 12.5 mg L^-1, the corresponding open circuit voltage and maximum power density were 0.78 V and 10.2 W m^-3, respectively. The mechanism analysis demonstrated that microbial electrochemical reduction contributed to the copper removal with the products of Cu and Cu₂O deposited at biocathode. Moreover, the microbial community analysis indicated that microbial communities changed with different copper concentrations. The dominant phyla were Proteobacteria and Bacteroidetes which could play key roles in electricity generation, while Actinobacteria and Acidobacteria were also observed which were responsible for Cu-resistant and copper removal. It will be of important guiding significance for the recovery of copper from low concentration wastewater through single-chamber MFC with simultaneous energy recovery.

Continuous energy recovery and nutrients removal from molasses wastewater by synergistic system of dark fermentation and algal culture under various fermentation types

Synergistic system of dark fermentation and algal culture was initially operated at batch mode to investigate the energy production and nutrients removal from molasses wastewater in butyrate-type, ethanol-type and propionate-type fermentations. Butyrate-type fermentation was the most appropriate fermentation type for the synergistic system and exhibited the accumulative hydrogen volume of 658.3 mL L^-1 and hydrogen yield of 131.7 mL g^-1 COD. By-products from dark fermentation (mainly acetate and butyrate) were further used to cultivate oleaginous microalgae. The maximum algal biomass and lipid content reached 1.01 g L^-1 and 38.5%, respectively. In continuous operation, the synergistic system was stable and efficient, and energy production increased from 8.77 kJ L^-1 d^-1 (dark fermentation) to 17.3 kJ L^-1 d^-1 (synergistic system). Total COD, TN and TP removal efficiencies in the synergistic system reached 91.1%, 89.1% and 85.7%, respectively. This study shows the potential of the synergistic system in energy recovery and wastewater treatment.

Overexpression of a tomato carotenoid ε-hydroxylase gene (SlLUT1) improved the drought tolerance of transgenic tobacco

Drought stress is a considerable environmental factor that restrains photosynthesis. Lutein, the most prolific carotenoid in plant photosynthetic tissues, plays vital roles in the light-harvesting complexes. However, its biological functions under abiotic stresses remain unclear. In our research, transgenic tobacco plants were utilized to investigate the function of the tomato chloroplast-targeted carotenoid epsilon-ring hydroxylase (SlLUT1) in drought stress tolerance. The analysis of SlLUT1-pro-LUC and qRT-PCR showed that drought stress induced SlLUT1 expression. Transgenic tobacco plants exhibit higher lutein content than wild-type (WT) tobacco. Under drought stress, transgenic plants overexpressing SlLUT1 showed better growth performance, higher chlorophyll and relative water contents and more intact chloroplast and PSII supercomplex structures than WT tobacco. The Fv/Fm, Pn, NPQ, and content of D1 protein in transgenic plants were higher than those in WT plants under drought stress. The accumulation of H2O2 and O2- decreased in transgenic tobacco plants. Moreover, transgenic plants exhibited lower MDA accumulation and REL. These results indicate that overexpression of SlLUT1 enhances tolerance to drought stress by maintaining photosynthesis and scavenging ROS in transgenic tobacco.

SlCOR413IM1: A novel cold-regulation gene from tomato, enhances drought stress tolerance in tobacco

Drought stress adversely affects plant growth, development, and productivity. Genes functioning in plant response to drought stress are essential for drought tolerance. In this study, SlCOR413IM1, a cold-regulated gene isolated from Solanum lycopersium, was transferred to Nicotiana tabacum to investigate its function under drought stress. The subcellular localisation of SlCOR413IM1-GFP fusion protein in Arabidopsis protoplasts suggested that SlCOR413IM1 is a chloroplast protein. Expression analyses revealed that SlCOR413IM1 responded to drought and cold stresses. Under drought stress, transgenic plants maintained the high maximum photochemical efficiency, net photosynthetic rate (Pn) and D1 protein content of photosystem II (PSII). Compared with wild-type (WT) plants, transgenic plants showed higher superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities and proline and soluble sugar content, which reduced reactive oxygen species (ROS) generation. However, the high SOD and APX activities in transgenic plants were independent of their transcription levels. Moreover, the transgenic plants exhibited better seed germination, water status and survival, as well as lower malondialdehyde (MDA) content and relative electrical conductivity (REC) than WT plants under drought stress. Taken together, these data demonstrated that overexpression of SlCOR413IM1 enhanced drought stress tolerance in transgenic tobacco.

A stress-associated NAC transcription factor (SlNAC35) from tomato plays a positive role in biotic and abiotic stresses

The NAC transcription factor family participates in responses to various kinds of environmental stimuli in plants. Responses of NAC genes to abiotic stresses have been widely studied, but their functions in response to biotic stress are little reported in plants, especially in crops. In the present study, we examined the functions of a novel tomato (Solanum lycopersicum) NAC protein (SlNAC35) in abiotic and biotic stress resistance by using transgenic tobacco. Expression analysis found that SlNAC35 expression was induced by drought stress, salt stress, bacterial pathogen, and signaling molecules, suggesting its involvement in plant responses to biotic and abiotic stimuli. Moreover, transgenic lines exhibited a greater number of lateral roots and longer root length compared with Vec lines (empty vector lines) after drought and salt treatment. These results indicate that overexpression of SlNAC35 promoted root growth and development under drought and salt stresses. Higher expressions of NtARF1, NtARF2 and NtARF8 were observed under drought and salt stresses in transgenic lines, suggesting that overexpression of SlNAC35 promoted growth and development of roots in transgenic lines possibly by involving auxin signaling and by regulating NtARF expression. In addition, SlNAC35 overexpression improved resistance to bacterial pathogen in transgenic tobacco, and reactive oxygen species may be in the upstream of salicylic acid (SA) signaling in transgenic tobacco during defense response.