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Iron is an essential element for plant growth and development. While abundant in soil, the available Fe in soil is limited. In this regard, plants have evolved a series of mechanisms for efficient iron uptake, allowing plants to better adapt to iron deficient conditions. These mechanisms include iron acquisition from soil, iron transport from roots to shoots, and iron storage in cells. The mobilization of Fe in plants often occurs via chelating with phytosiderophores, citrate, nicotianamine, mugineic acid, or in the form of free iron ions. Recent work further elucidates that these genes’ response to iron deficiency are tightly controlled at transcriptional and posttranscriptional levels to maintain iron homeostasis. Moreover, increasing evidences shed light on certain factors that are identified to be interconnected and integrated to adjust iron deficiency. In this review, we highlight the molecular and physiological bases of iron acquisition from soil to plants and transport mechanisms for tolerating iron deficiency in dicotyledonous plants and rice.

Background MicroRNAs (miRNAs) are small, endogenous RNAs that play important regulatory roles in development and stress response in plants by negatively affecting gene expression post-transcriptionally. Identification of miRNAs at the global genome-level by high-throughout sequencing is essential to functionally characterize miRNAs in plants. Drought is one of the common environmental stresses limiting plant growth and development. To understand the role of miRNAs in response of plants to drought stress, drought-responsive miRNAs were identified by high-throughput sequencing in a legume model plant, Medicago truncatula . Results Two hundreds eighty three and 293 known miRNAs were identified from the control and drought stress libraries, respectively. In addition, 238 potential candidate miRNAs were identified, and among them 14 new miRNAs and 15 new members of known miRNA families whose complementary miRNA*s were also detected. Both high-throughput sequencing and RT-qPCR confirmed that 22 members of 4 miRNA families were up-regulated and 10 members of 6 miRNA families were down-regulated in response to drought stress. Among the 29 new miRNAs/new members of known miRNA families, 8 miRNAs were responsive to drought stress with both 4 miRNAs being up- and down-regulated, respectively. The known and predicted targets of the drought-responsive miRNAs were found to be involved in diverse cellular processes in plants, including development, transcription, protein degradation, detoxification, nutrient status and cross adaptation. Conclusions We identified 32 known members of 10 miRNA families and 8 new miRNAs/new members of known miRNA families that were responsive to drought stress by high-throughput sequencing of small RNAs from M. truncatula . These findings are of importance for our understanding of the roles played by miRNAs in response of plants to abiotic stress in general and drought stress in particular.

Key messageTransformation ofMruGSTU39inM. ruthenicaand alfalfa enhanced growth and survival of transgenic plants by up-regulating GST and glutathione peroxidase activity to detoxify ROS under drought stress. Glutathione S-transferases (GSTs) are ubiquitous supergene family which play crucial roles in detoxification of reactive oxygen species (ROS). Despite studies on GSTs, few studies have focused on them in perennial, wild plant species with high tolerance to environmental stress. Here, we identified 66 MruGST genes from the genome of Medicago ruthenica, a perennial legume species native to temperate grasslands with high tolerance to environmental stress. These genes were divided into eight classes based on their conserved domains, phylogenetic tree and gene structure, with the tau class being the most numerous. Duplication analysis revealed that GST family in M. ruthenica was expanded by segmental and tandem duplication. Several drought-responsive MruGSTs were identified by transcriptomic analyses. Of them, expression of MruGSTU39 was up-regulated much more in a tolerant accession by drought stress. Transformation of MruGSTU39 in M. ruthenica and alfalfa (Medicago sativa) enhanced growth and survival of transgenic seedlings than their wild-type counterparts under drought. We demonstrated that MruGSTU39 can detoxify ROS to reduce its damage to membrane by up-regulating activities of GST and glutathione peroxidase. Our findings provide full-scale knowledge on GST family in the wild legume M. ruthenica with high tolerance to drought, and highlight improvement tolerance of legume forages to drought using genomic information of M. ruthenica.

Western Hubei Province, China, lies in the transition zone between the second and third topographic steps of China’s terrain ladder system. Influenced by the deep incision of the Yangtze River and its tributaries, numerous high-steep slopes have been widely developed in this region.This study focuses on the Heicao dangerous rock mass in Xingshan County, Hubei Province. Through field investigations and Unmanned Aerial Vehicle (UAV) photogrammetry, a discrete element numerical model was developed to investigate the progressive failure mechanisms of high-steep dangerous rock masses under varying lengths of the main structural plane.This study will contribute to future prevention and control of such hazardous rock disasters.The principal conclusions are as follows: (1) The failure surface of the Heicao rock mass exhibits composite form,with the upper section displaying a polyline geometry and the lower section approximating an arc-shaped profile. (2) The main structural plane length significantly affects both the damage extent and propagation velocity in the upper rock mass. (3) Dangerous rock mass instability is jointly influenced by the basal rock mass and the overlying rock mass. Under gravity, progressive failure of the basal rock mass triggers crack development and anti-sliding force attenuation, while main structural plane propagation exacerbates damage. Ultimately, rock bridge shearing and crack coalescence lead to the formation of a progressively penetrating failure surface, resulting in global instability. (4) The results of this study have important theoretical and practical implications for future geological disaster assessment and prevention. In particular, the effective protection of the basement rock mass is the key factor to prevent the formation of dangerous rock mass disasters.

To investigate the damage mechanisms in granite’s physical and mechanical properties after high-temperature water quenching, this study employed MTS815.04 for uniaxial compression tests on thermally treated specimens, with concurrent acoustic emission monitoring, and utilized nanoindentation for micromechanical analysis. The results show that with increasing temperature, granite's peak strength and elastic modulus decrease, with a sharp decline after 400–500 °C, corresponding to a significant increase in the internal damage, which can be detected by acoustic emission monitoring. Below 500 °C, macroscopic mechanical degradation is due to mineral thermophysical property differences, while above 500 °C, microcrack development is the main deterioration factor. The failure mode shifts from tensile to tensile-shear complex to shear failure, with transition points at 400 °C and 800 °C. The results of this study are of certain reference value for improving the efficiency of extracting thermal energy from dry-hot rocks and providing security guidance for the tunnel restoration process following fire damage.

Background Medicago ruthenica , a wild and perennial legume forage widely distributed in semi-arid grasslands, is distinguished by its outstanding tolerance to environmental stress. It is a close relative of commonly cultivated forage of alfalfa ( Medicago sativa ). The high tolerance of M. ruthenica to environmental stress makes this species a valuable genetic resource for understanding and improving traits associated with tolerance to harsh environments. Results We sequenced and assembled genome of M. ruthenica using an integrated approach, including PacBio, Illumina, 10×Genomics, and Hi-C. The assembled genome was 904.13 Mb with scaffold N50 of 99.39 Mb, and 50,162 protein-coding genes were annotated. Comparative genomics and transcriptomic analyses were used to elucidate mechanisms underlying its tolerance to environmental stress. The expanded FHY3/FAR1 family was identified to be involved in tolerance of M. ruthenica to drought stress. Many genes involved in tolerance to abiotic stress were retained in M. ruthenica compared to other cultivated Medicago species. Hundreds of candidate genes associated with drought tolerance were identified by analyzing variations in single nucleotide polymorphism using accessions of M. ruthenica with varying tolerance to drought. Transcriptomic data demonstrated the involvements of genes related to transcriptional regulation, stress response, and metabolic regulation in tolerance of M. ruthenica. Conclusions We present a high-quality genome assembly and identification of drought-related genes in the wild species of M. ruthenica , providing a valuable resource for genomic studies on perennial legume forages.

Legume plants produce one-third of the total yield of primary crops and are important food sources for both humans and animals worldwide. Frequent exposure to abiotic stresses, such as drought, salt, and cold, greatly limits the production of legume crops. Several morphological, physiological, and molecular studies have been conducted to characterize the response and adaptation mechanism to abiotic stresses. The tolerant mechanisms of the model legume plant Medicago truncatula to abiotic stresses have been extensively studied. Although many potential genes and integrated networks underlying the M. truncatula in responding to abiotic stresses have been identified and described, a comprehensive summary of the tolerant mechanism is lacking. In this review, we provide a comprehensive summary of the adaptive mechanism by which M. truncatula responds to drought, salt, and cold stress. We also discuss future research that need to be explored to improve the abiotic tolerance of legume plants.

Electric buses (EBs) have been implemented worldwide and exhibited great potential for air pollution reduction and traffic noise control. In regular charging scenarios, the deployment of charging facilities and the operational scheduling of the transit system is crucial to bus transit system management. In this paper, we proposed a joint optimization model of regular charging electric bus transit network schedule and stationary charger deployment considering partial charging policy and time-of-use electricity prices. The objective of the model is to minimize the total investment cost of the transit system including the capital and maintenance cost of EBs and chargers, the power consumption cost, and time-related in-service cost. A solving procedure based on the improved adaptive genetic algorithm (AGA) is further designed and a transit network at inner Anting Town, Shanghai, with 8 individual bus routes and 867 daily service trips is adopted for the model validation. The validation results illustrated that the methodology considering the partial charging policy can arrange the charging schedule adaptive to the time-of-use electricity prices. Compared with the benchmark of single line separate scheduling, the proposed model can yield 3 million RMB investment saving by highly utilizing EBs and battery chargers.

MicroRNAs (miRNAs) play important roles in response of plants to biotic and abiotic stresses. Aluminum (Al) toxicity is a major factor limiting plant growth in acidic soils. However, there has been limited report on the involvement of miRNAs in response of plants to toxic Al³⁺. To identify Al³⁺-responsive miRNAs at wholegenome level, high-throughput sequencing technology was used to sequence libraries constructed from root apices of the model legume plant Medicago truncatula treated with and without Al³⁺. High-throughput sequencing of the control and two Al³⁺-treated libraries led to generation of 17.1, 14.1 and 17.4 M primary reads, respectively. We identified 326 known miRNAs and 21 new miRNAs. Among the miRNAs, expression of 23 miRNAs was responsive to Al³⁺, and the majority of Al³⁺-responsive mRNAs was down-regulated. We further classified the Al³⁺-responsive miRNAs into three groups based on their expression patterns: rapid-responsive, late-responsive and sustained-responsive miRNAs. The majority of Al³⁺-responsive miRNAs belonged to the 'rapid-responsive' category, i.e. they were responsive to short-term, but not long-term Al³⁺ treatment. The Al³⁺-responsive miRNAs were also verified by quantitative real-time PCR. The potential targets of the 21 new miRNAs were predicted to be involved in diverse cellular processes in plants, and their potential roles in Al³⁺-induced inhibition of root growth were discussed. These findings provide valuable information for functional characterization of miRNAs in Al³⁺ toxicity and tolerance.

Background Long non-coding RNAs (lncRNAs) play important roles in the regulation of plant responses to environmental stress by acting as essential regulators of gene expression. However, whether and how lncRNAs are involved in cold acclimation-dependent freezing tolerance in plants remains largely unknown. Medicago truncatula is a prominent model for studies of legume genomics, and distinguished by its cold-acclimation characteristics. To determine the roles of lncRNAs in plant cold stress response, we conducted genome-wide high-throughput sequencing in the legume model plant M. truncatula . Results RNA-seq data were generated from twelve samples for the four treatments, i.e., non-cold treated leaves and roots, cold-treated leaves and roots of M. truncatula Jemalong A17 seedlings. A total of 1204 million raw reads were generated. Of them, 1150 million filtered reads after quality control (QC) were subjected to downstream analysis. A large number of 24,368 unique lncRNAs were identified from the twelve samples. Among these lncRNAs, 983 and 1288 were responsive to cold treatment in the leaves and roots, respectively. We further found that the intronic-lncRNAs were most sensitive to the cold treatment. The cold-responsive lncRNAs were unevenly distributed across the eight chromosomes in M. truncatula seedlings with obvious preferences for locations. Further analyses revealed that the cold-responsive lncRNAs differed between leaves and roots. The putative target genes of the lncRNAs were predicted to mainly involve the processes of protein translation, transport, metabolism and nucleic acid transcription. Furthermore, the networks of a tandem array of CBF/DREB1 genes that were reported to be located in a major freezing tolerance QTL region on chromosome 6 and their related lncRNAs were dissected based on their gene expression and chromosome location. Conclusions We identified a comprehensive set of lncRNAs that were responsive to cold treatment in M. truncatula seedlings, and discovered tissue-specific cold-responsive lncRNAs in leaves and roots. We further dissected potential regulatory networks of CBF Intergenic RNA ( MtCIR1 ) and MtCBF s that play critical roles in response and adaptation of M. truncatula to cold stress.