Structural insights into ion selectivity and transport mechanisms of Oryza sativa HKT2;1 and HKT2;2/1 transporters.

Plant high-affinity K+ transporters (HKTs) play a pivotal role in maintaining the balance of Na+ and K+ ions in plants, thereby influencing plant growth under K+-depleted conditions and enhancing tolerance to salinity stress. Here we report the cryo-electron microscopy structures of Oryza sativa HKT2;1 and HKT2;2/1 at overall resolutions of 2.5 Å and 2.3 Å, respectively. Both transporters adopt a dimeric assembly, with each protomer enclosing an ion permeation pathway. Comparison between the selectivity filters of the two transporters reveals the critical roles of Ser88/Gly88 and Val243/Gly243 in determining ion selectivity. A constriction site along the ion permeation pathway is identified, consisting of Glu114, Asn273, Pro392, Pro393, Arg525, Lys517 and the carboxy-terminal Trp530 from the neighbouring protomer. The linker between domains II and III adopts a stable loop structure oriented towards the constriction site, potentially participating in the gating process. Electrophysiological recordings, yeast complementation assays and molecular dynamics simulations corroborate the functional importance of these structural features. Our findings provide crucial insights into the ion selectivity and transport mechanisms of plant HKTs, offering valuable structural templates for developing new salinity-tolerant cultivars and strategies to increase crop yields.

Recent Advances of Emerging Spleen-Targeting Nanovaccines for Immunotherapy.

Vaccines provide a powerful tool to modulate the immune system for human disease prevention and treatment. Classical vaccines mainly initiate immune responses in the lymph nodes (LNs) after subcutaneous injection. However, some vaccines suffer from inefficient delivery of antigens to LNs, undesired inflammation, and slow immune induction when encountering the rapid proliferation of tumors. Alternatively, the spleen, as the largest secondary lymphoid organ with a high density of antigen-presenting cells (APCs) and lymphocytes, acts as an emerging target organ for vaccinations in the body. Upon intravenous administration, the rationally designed spleen-targeting nanovaccines can be internalized by the APCs in the spleen to induce selective antigen presentation to T and B cells in their specific sub-regions, thereby rapidly boosting durable cellular and humoral immunity. Herein, the recent advances of spleen-targeting nanovaccines for immunotherapy based on the anatomical architectures and functional zones of the spleen, as well as their limitations and perspectives for clinical applications are systematically summarized. The aim is to emphasize the design of innovative nanovaccines for enhanced immunotherapy of intractable diseases in the future.

The Apple microR171i-SCARECROW-LIKE PROTEINS26.1 Module Enhances Drought Stress Tolerance by Integrating Ascorbic Acid Metabolism.

Drought stress severely restricts crop yield and quality. Small noncoding RNAs play critical roles in plant growth, development, and stress responses by regulating target gene expression, but their roles in drought stress tolerance in apple (Malus domestica) are poorly understood. Here, we identified various small noncoding RNAs and their targets from the wild apple species Malus sieversii via high-throughput sequencing and degradome analysis. Forty known microRNAs (miRNAs) and eight new small noncoding RNAs were differentially expressed in response to 2 or 4 h of drought stress treatment. We experimentally verified the expression patterns of five selected miRNAs and their targets. We established that one miRNA, mdm-miR171i, specifically targeted and degraded SCARECROW-LIKE PROTEINS26 1 (MsSCL26 1) transcripts. Both knockout of mdm-miR171i and overexpression of MsSCL26 1 improved drought stress tolerance in the cultivated apple line 'GL-3' by regulating the expression of antioxidant enzyme genes, especially that of MONODEHYDROASCORBATE REDUCTASE, which functions in metabolism under drought stress. Transient expression analysis demonstrated that MsSCL26.1 activates MsMDHAR transcription by positively regulating the activity of the P1 region in its promoter. Therefore, the miR171i-SCL26 1 module enhances drought stress tolerance in apple by regulating antioxidant gene expression and ascorbic acid metabolism.

Overexpression of MsGH3.5 inhibits shoot and root development through the auxin and cytokinin pathways in apple plants.

Phytohormonal interactions are crucial for plant development. Auxin and cytokinin (CK) both play critical roles in regulating plant growth and development; however, the interaction between these two phytohormones is complex and not fully understood. Here, we isolated a wild apple (Malus sieversii Roem) GRETCHEN HAGEN3 (GH3) gene, MsGH3.5, encoding an indole-3-acetic acid (IAA)-amido synthetase. Overexpression of MsGH3.5 significantly reduced the free IAA content and increased the content of some IAA-amino acid conjugates, and MsGH3.5-overexpressing lines were dwarfed and produced fewer adventitious roots (ARs) than the control. This phenotype is consistent with the role of GH3 in conjugating excess free active IAA to amino acids in auxin homeostasis. Surprisingly, overexpression of MsGH3.5 significantly increased CK concentrations in the whole plant, and altered the expression of genes involved in CK biosynthesis, metabolism and signaling. Furthermore, exogenous CK application induced MsGH3.5 expression through the activity of the CK type-B response regulator, MsRR1a, which mediates the CK primary response. MsRR1a activated MsGH3.5 expression by directly binding to its promoter, linking auxin and CK signaling. Plants overexpressing MsRR1a also displayed fewer ARs, in agreement with the regulation of MsGH3.5 expression by MsRR1a. Taken together, we reveal that MsGH3.5 affects apple growth and development by modulating auxin and CK levels and signaling pathways. These findings provide insight into the interaction between the auxin and CK pathways, and might have substantial implications for efforts to improve apple architecture.

[Multi-year measurement of soil respiration components in a subtropical secondary forest].

A four-year field experiment was performed from March 2010 to February 2014 in order to investigate the contribution of different respiratory components to soil respiration and the temperature sensitivity of different respiratory components. Four blocks were arranged in field, and there were trenched and un-trenched plots in each block. Trenching, which can exclude roots, was performed around the trenched plots. A portable soil CO2 fluxes system ( Li-8100) was used to measure soil respiration rates. Soil temperature and soil moisture were simultaneously observed when measuring soil respiration rates. The results showed that the heterotrophic respiration rate in the trenched plots and the soil respiration rate in the un-trenched plots had the same seasonal pattern. Soil respiration rate in the un-trenched plots was significantly (P < 0.001) higher than that in the trenched plots. Mean soil respiration rates in untrenched plots and mean heterotrophic respiration rate in trenched plots were (2.59 ± 0.48 ) and (1.74 ± 0.28) µmol x (M2 x s)(-1), respectively. There was no significant (P > 0.05) difference in the mean soil respiration rate or mean heterotrophic respiration rate between measurement years. The relationship between heterotrophic respiration and soil respiration could be fitted with a proportion function. Heterotrophic and autotrophic respiration contributed 65.9% and 34.1% to the soil respiration, respectively. The main contributor to soil respiration was heterotrophic respiration. The relationship between the ratio of heterotrophic respiration to soil respiration and measurement date could be fitted with a linear function. An exponential function could be used to fit the relationship between heterotrophic respiration and soil temperature, and between autotrophic respiration and soil temperature. The temperature sensitivity coefficient (Q10) for heterotrophic respiration was lower than that for autotrophic respiration.

[Effects of simulated warming on soil respiration in a cropland under winter wheat-soybean rotation].

This study was aimed to investigate the effects of simulated warming on soil respiration in a cropland under winter wheat-soybean rotation. Randomized experiments were carried out in the cropland. 6 Plots were arranged and there were 2 treatments, simulated warming and control. A portable soil CO2 fluxes system (LI-8100) was used to measure soil respiration rates. Soil CO2 production rates were determined by using a Barometric Process Separation (BaPS) method. Soil temperature and soil moisture were simultaneously determined when measuring soil respiration rates. Results indicated that soil respiration rates in different treatments showed similar seasonal variability, in accordance with the variability in soil temperature. Seasonal mean soil respiration rates for simulated warming and control treatments were 3.54 and 2.49 micromol x (m2 x s)(-1), respectively, during the winter wheat growth season, while they were 4.80 and 4.14 micromol x (m2 x s)(-1), respectively, during the soybean growth season. Simulated warming significantly (P < 0.05) enhanced soil respiration during both the winter wheat and soybean growth seasons. The impact of simulated warming on soil respiration was particularly obvious during the later growth stages of winter wheat (from heading to maturity stages) and soybean (from flowing to maturity stages). Further investigations suggested that, for both the winter wheat and soybean growth seasons, the relationship between soil respiration and soil temperature could be well explained (P < 0.01) by exponential functions. The temperature sensitivity (Q10) of soil respiration in the simulated warming treatments was significantly higher than that in the control treatments. The Q10 values for the simulated warming and control treatments were 1.83 and 1.26, respectively, during the winter wheat growth season, while they were 2.85 and 1.70, respectively, during the soybean growth season. This study showed that simulated warming significantly increased soil respiration in the cropland.

[Review of the factors influencing the temporal and spatial variability of soil respiration in terrestrial ecosystem].

Soil respiration is an important process in carbon cycling. Understanding the processes and controlling factors of soil respiration are crucial in investigating the terrestrial carbon cycling. This article reviews the investigations about the factors controlling the temporal and spatial variability of soil respiration. The temporal and spatial variability in soil respiration is linked with climate, vegetation and soil factors. Air temperature and precipitation generally contribute great to the variability of soil respiration. Leaf area index (LAI), litter fall and fine root biomass are three plant-related factors that can be employed to explained the variability of soil respiration, while soil carbon content and texture are two soil factors responsible for the variability of soil respiration. Generally, climate, vegetation and soil factors contribute collectively to the temporal and spatial variability of terrestrial soil respiration. Temperature and precipitation, on the one hand, directly affect the root and microbial respiration rates. On the other hand, temperature and precipitation indirectly affect soil respiration by influencing the plant and microbial growth and soil conditions. In order to understand the controlling factors of the temporal and spatial variability of soil respiration, there are four main issues need to be addressed. The issues include quantitatively partitioning the autotrophic and heterotrophic components of soil respiration, standardizing the method and scale of measuring soil respiration, coupling measurements of soil respiration with environmental factors and performing more measurements of soil respiration in wetland ecosystems.

[Investigation of heterotrophic and autotrophic components of soil respiration in a secondary forest in subtropical China].

Trenched plots were set up in 2010 in a secondary forest in subtropical China, in order to investigate the seasonal variations of soil respiration (R(s)) and heterotrophic respiration (R(h)). Autotrophic respiration (R(a)) was estimated to be the difference between R(s) and R(h). Soil temperature and moisture were simultaneously measured during respiration measurements. Results indicated that R(s) and R(h) showed the similar seasonal variations. Seasonal mean rates for R(s), R(h) and R(a) were 3.42, 2.36 and 1.06 micromol x (m2 x s)(-1), respectively. Regression analysis indicated that R(h) increased with the increase of R(s); an natural logistic equation could be employed to explained the relationship between R(h) (y) and R(s) (x). Approximately 90.5% (R2 = 0.905) variations in R(h) could be explained by the equation. Apparent exponential relationships of R(h) and R(a) with soil temperature existed, but differed from each other and from the relationship for R(s). The exponential equations explained about 78.4%, 76.4% and 65.6% variations in R(s), R(h) and R(a), respectively, with the P values less than 0.01. The Q10 values for R(s), R(h) and R(a) were 1.97, 1.76 and 3.31, respectively. It was indicated that, seasonally, R(h) and R(a) represented 69% and 31% of R(s). R(a) showed significantly higher temperature sensitivity than R(h).

[Effects of elevated ozone concentration on soil respiration, nitrification and denitrification in a winter wheat farmland].

Field experiments were carried out in a winter wheat farmland, in order to investigate the effects of elevated ozone concentration on soil respiration, nitrification and denitrification. Three ozone concentration treatments, which were CK, T1 (100 nL x L(-1)) and T2 (150 nL x L(-1)), were arranged using open top chambers (OTCs). A portable soil CO2 fluxes system was used to measure soil respiration rates. Nitrification and denitrification rates were determined by using a Barometric Process Separation (BaPS) method. Results indicated that there were no significant differences (p > 0.05) in soil respiration rates among CK, T1 and T2 treatments. Mean soil respiration rates for CK, T1 and T2 treatments were (5.36 +/- 0.72), (5.08 +/- 0.04), (4.94 +/- 0.18) micromol x (m2 x s)(-1), respectively. No significant differences (p > 0.05) in mean soil nitrification and denitrification rates were observed between the treatments of CK and T2. During the experimental period, soil respiration showed an exponential relationship with soil temperature for each of the treatment. The Q10 (the respiratory flux at one temperature over the flux at a temperature 10 degrees C lower) values were 1.72, 1.58 and 1.51 for CK, T1 and T2 treatments, respectively. A correlation (Pearson product-momentum correlation) analysis showed that soil water content was correlated significantly (p < 0.05) with soil nitrification (r = 0.828) and denitrification (r = 0.890) rates for CK treatment. Soil water content was correlated significantly (p < 0.05) with soil nitrification rate for T2 treatment, with the correlation coefficient of 0.772. This study indicated that elevated ozone concentration did not significantly affect soil respiration, nitrification and denitrification rates in the winter wheat farmland. Elevated ozone concentration, however, significantly reduced the temperature sensitivity of soil respiration.