High-temperature stress can cause serious abiotic damage that limits the yield and quality of rice. Heat tolerance (HT) during the flowering stage of rice is a key trait that can guarantee a high and stable yield under heat stress. HT is a complex trait that is regulated by multiple quantitative trait loci (QTLs); however, few underlying genes have been fine mapped and cloned. In this study, the F2:3 population derived from a cross between Huanghuazhan (HHZ), a heat-tolerant cultivar, and 9311, a heat-sensitive variety, was used to map HT QTLs during the flowering stage in rice. A new major QTL, qHTT8, controlling HT was identified on chromosome 8 using the bulked-segregant analysis (BSA)-seq method. The QTL qHTT8 was mapped into the 3,555,000-4,520,000 bp, which had a size of 0.965 Mb. The candidate region of qHTT8 on chromosome 8 contained 65 predicted genes, and 10 putative predicted genes were found to be associated with abiotic stress tolerance. Furthermore, qRT-PCR was performed to analyze the differential expression of these 10 genes between HHZ and 9311 under high temperature conditions. LOC_Os08g07010 and LOC_Os08g07440 were highly induced in HHZ compared with 9311 under heat stress. Orthologous genes of LOC_Os08g07010 and LOC_Os08g07440 in plants played a role in abiotic stress, suggesting that they may be the candidate genes of qHTT8. Generally, the results of this study will prove useful for future efforts to clone qHTT8 and breed heat-tolerant varieties of rice using marker-assisted selection.

The excessive use of synthetic nitrogen (N) fertilizers in rice (Oryza sativa L.) has resulted in high N loss, soil degradation, and environmental pollution in a changing climate. Soil biochar amendment is proposed as a climate change mitigation tool that supports carbon sequestration and reduces N losses and greenhouse gas (GHG) emissions from the soil. The current study evaluated the impact of four different rates of biochar (B) (C/B0-0 t ha-1, B1-20 t ha-1, B2-40 t ha-1, and B3-60 t ha-1) and two N levels (N1; low (270 kg N ha-1) and N2; high (360 kg N ha-1)), on rice (cultivar Zhenguiai) grown in pots. Significant increases in the average soil microbial biomass N (SMBN) (88%) and carbon (87%) were recorded at the highest rate of 60-ton ha-1B and 360 kg N ha-1 compared to the control (N1C) during both seasons (S1 and S2). The photochemical efficiency (Fv/Fm), quantum yield of the photosystem (PS) II (ΦPS II), electron transport rate (ETR), and photochemical quenching (qP) were enhanced at low rates of biochar applications (20 to 40 t B ha-1) for high and low N rates across the seasons. Nitrate reductase (NR), glutamine synthetase (GS), and glutamine 2-oxoglutarate aminotransferase (GOGAT) activity were, on average, 39%, 55%, and 63% higher in the N1B3, N2B2, and N2B3 treatments, respectively than the N1C. The grain quality was higher in the N1B3 treatment than the N1C, i.e., the protein content (PC), amylose content (AC), percent brown rice (BRP), and percent milled rice (MRP) were, on average, 16%, 28%, 4.6%, and 5% higher, respectively in both seasons. The results of this study indicated that biochar addition to the soil in combination with N fertilizers increased the dry matter (DM) content, N uptake, and grain yield of rice by 24%, 27%, and 64%, respectively, compared to the N1C.

Endothelial cell damage is an important pathological basis for the deterioration of acute ischemia stroke. Our previous studies have been exploring the mechanism of blood-brain barrier (BBB) endothelial cell injury in the early stage of cerebral ischemia. Exosomes act as an important intercellular player in neurovascular communication. However, the characteristic of exosomes derived from BBB endothelial cells in early ischemic stroke is poorly understood. We exposed cultured brain microvascular endothelial cells (bEnd.3) to 3 h oxygen glucose deprivation (OGD) to mimic early cerebral ischemia in vitro and compared miRome and surface protein contents of exosomes derived from bEnd.3 cells by miRNA sequencing and the proximity barcoding assay (PBA). A total of 346 differentially miRNA (159 upregulated and 187 downregulated) were identified via miRNA-Seq in bEnd.3 cells after exposure to OGD for 3 h. Moreover, Gene Ontology (GO) and KEGG pathway analyses showed that cell proliferation- and angiogenesis-associated miRNAs were significantly affected. The abnormal changes in top eight miRNAs were further verified by a quantitative polymerase chain reaction (qPCR). PBA experiments showed that the numbers of exosomes carrying the following proteins increased significantly under ischemia, including bFGF, CD146, EPHA2, ABCB5, and ITGB2. These proteins were related to angiogenesis, cell proliferation, and cell inflammation. The network analysis combining PBA data with miRNA-Seq data showed that 79 miRNAs were related to 24 membrane proteins and predicted that there were surface proteins associated with a variety of miRNA molecules, such as ITGA9, XIAP, ADAM1, ITGA2, ITGA3, PDPN, and ITGB1. Meanwhile, there were miRNAs related to various surface proteins including miR-410-3p, miR-378b, and miR-1960. Taken together, our data demonstrated for the first time the changes of exosomal miRNAs and surface protein profiles derived from ischemic microvascular endothelial cells, which may provide new therapeutic targets for BBB protection in ischemic stroke.

The number of seedlings per hill and the configuration of plant row spacing are important management measures to improve rice yield. In the present study, we evaluated the impact of various seedlings per hill (1, 3, 6, and 9 seedlings hill-1) under four different rice verities (two conventional rice, two hybrid rice) on allometric characteristics, nitrogen use efficiency (NUE) and yield in 2020 at early and late season. Results showed that compared with nine seedlings per hill (wide row spacing), the number of effective panicles, yield, grain biomass allocation, grain-to-leaf ratio, grain nitrogen accumulation, nitrogen dry matter production efficiency (NDMPE), N harvest index (NHI) of 1 seedling per hill increased by 21.8%, 10.91%, 10.5%, 32.25%, 17.03%, 9.67%, 6.5%, respectively. With the increase of seedlings per hill and the expansion of row spacing, stem biomass (SB) and reproductive biomass (RB) increased with the increase of above-ground biomass, mainly showing the relationship of isometric growth. Leaf biomass (LB) increased with above-ground biomass, mainly showing the relationship of allometric growth. The results suggested that under the same basic seedlings, transplanting 1 seedling per hill and dense planting was the most beneficial to improve rice yield.

Leaf nitrogen (N) concentration plays an important role in biochemical and physiological functions, and N availability directly influences rice yield. However, excessive N fertilization is considered to be a root cause of environmental issues and low nitrogen use efficiency. Therefore, the selection of appropriate nutrient management practices and organic amendments is key to maximizing nitrogen uptake and maintaining high and sustainable rice production. Here, we evaluated the effects of different 15N-labelled nitrogen sources (urea, ammonium nitrate, and ammonium sulfate at 315 kg ha-1) with or without biochar (30 t ha-1) on paddy soil properties, root growth, leaf gas exchange, N metabolism enzymes, and N uptake in the early and late seasons of 2019. We found significant differences among N fertilizer sources applied with or without biochar (P < 0.05). Across the seasons, the combination of biochar with N fertilizers significantly increased soil organic carbon by 51.21% and nitrogen availability by 27.51% compared with N fertilizers alone. Correlation analysis showed that rice root morphological traits were strongly related to soil chemical properties, and higher root growth was measured in the biochar treatments. Similarly, net leaf photosynthetic rate averaged 9.34% higher, chlorophyll (Chl) a concentration 12.91% higher, and Chl b concentration 10.05% higher in the biochar treatments than in the biochar-free treatments across the seasons. Notably, leaf 15N concentration was 23.19% higher in the biochar treatments in both seasons. These results illustrated higher activities of N metabolism enzymes such as NR, GS, and GOGAT by an average 23.44%, 11.26% and 18.16% in the biochar treatments across the seasons, respectively. The addition of biochar with synthetic N fertilizers is an ecological nutrient management strategy that can increase N uptake and assimilation by ameliorating soil properties and improving the morpho-physiological factors of rice.

Biochar is an important soil amendment that can enhance the biological properties of soil, as well as nitrogen (N) uptake and utilization in N-fertilized crops. However, few studies have characterized the effects of urea and biochar application on soil biochemical traits and its effect on paddy rice. Therefore, a field trial was conducted in the early and late seasons of 2020 in a randomized complete block design with two N levels (135 and 180 kg ha-1) and four levels of biochar (0, 10, 20, and 30 t ha-1). The treatment combinations were as follows: 135 kg N ha-1 + 0 t B ha-1 (T1), 135 kg N ha-1 + 10 t B ha-1 (T2), 135 kg N ha-1 + 20 t B ha-1 (T3), 135 kg N ha-1 + 30 t B ha-1 (T4), 180 kg N ha-1 + 0 t B ha-1 (T5), 180 kg N ha-1 + 10 t B ha-1 (T6), 180 kg N ha-1 + 20 t B ha-1 (T7) and 180 kg N ha-1 + 30 t B ha-1 (T8). The results showed that soil amended with biochar had higher soil pH, soil organic carbon content, total nitrogen content, and mineral nitrogen (NH4+-N and NO3--N) than soil that had not been amended with biochar. In both seasons, the 20 t ha-1 and 30 t ha-1 biochar treatments had the highest an average concentrations of NO3--N (10.54 mg kg-1 and 10.25 mg kg-1, respectively). In comparison to soil that had not been treated with biochar, the average activity of the enzymes urease, polyphenol oxidase, dehydrogenase, and chitinase was, respectively, 25.28%, 14.13%, 67.76%, and 22.26% greater; however, the activity of the enzyme catalase was 15.06% lower in both seasons. Application of biochar considerably increased the abundance of ammonia-oxidizing bacteria (AOB), which was 48% greater on average in biochar-amended soil than in unamended soil. However, there were no significant variations in the abundances of ammonia-oxidizing archaea (AOA) or nitrite-oxidizing bacteria (NOB) across treatments. In comparison to soil that had not been treated with biochar, the average N content was 24.46%, 20.47%, and 19.08% higher in the stem, leaves, and panicles, respectively. In general, adding biochar at a rate of 20 to 30 t ha-1 with low-dose urea (135 kg N ha-1) is a beneficial technique for improving the nutrient balance and biological processes of soil, as well as the N uptake and grain yield of rice plants.