Alkaline Stress Tolerance Research Articles

Responses of growth and photosynthesis to alkaline stress in three willow species

Investigating differences in resistance to alkaline stress among three willow species can provide a theoretical basis for planting willow in saline soils. Therefore we tested three willow species (Salix matsudana, Salix gordejevii and Salix linearistipularis), already known for their high stress tolerance, to alkaline stress environment at different pH values under hydroponics. Root and leaf dry weight, root water content, leaf water content, chlorophyll content, photosynthesis and chlorophyll fluorescence of three willow cuttings were monitored six times over 15 days under alkaline stress. With the increase in alkaline stress, the water retention capacity of leaves of the three species of willow cuttings was as follows: S. matsudana > S. gordejevii > S. linearistipularis and the water retention capacity of the root system was as follows: S. gordejevii > S. linearistipularis > S. matsudana. The chlorophyll content was significantly reduced, damage symptoms were apparent. The net photosynthetic rate (Pn), rate of transpiration (E), and stomatal conductance (Gs) of the leaves showed a general trend of decreasing, and the intercellular CO2 concentration (Ci) of S. matsudana and S. gordejevii first declined and then tended to level off, while the intercellular CO2 concentration of S. linearistipularis first declined and then increased. The quantum yield and energy allocation ratio of the leaf photosystem II (PSII) reaction centre changed significantly (φPo, Ψo and φEo were obviously suppressed and φDo was promoted). The photosystem II (PSII) reaction centre quantum performance index and driving force showed a clear downwards trend. Based on the results it can be concluded that alkaline stress tolerance of three willow was as follows: S. matsudana > S. gordejevii > S. linearistipularis. However, since the experiment was done on young seedlings, further study at saplings stage is required to revalidate the results.

Exogenous melatonin delays leaves senescence and enhances saline and alkaline stress tolerance in grape seedlings

ABSTRACT Saline and alkaline stress is one of the major abiotic stresses facing agricultural production, which severely inhibits the growth and yield of plant. The application of plant growth regulators can effectively prevent crop yield reduction caused by saline and alkaline stress. Exogenous melatonin (MT) can act as a signaling molecule involved in the regulation of a variety of physiological processes in plants, has been found to play a key role in enhancing the improvement of plant tolerance to abiotic stresses. However, the effects of exogenous MT on saline and alkaline tolerance of table grape seedlings and its mechanism have not been clarified. The aim of this study was to investigate the role of exogenous MT on morphological and physiological growth of table grape seedlings ( Vitis vinifera L.) under saline and alkaline stress. The results showed that saline and alkaline stress resulted in yellowing and wilting of grape leaves and a decrease in chlorophyll content, whereas the application of exogenous MT alleviated the degradation of chlorophyll in grape seedling leaves caused by saline and alkaline stress and promoted the accumulation of soluble sugars and proline content. In addition, exogenous MT increased the activity of antioxidant enzymes, which resulted in the scavenging of reactive oxygen species (ROS) generated by saline and alkaline stress. In conclusion, exogenous MT was involved in the tolerance of grape seedlings to saline and alkaline stress, and enhanced the saline and alkaline resistance of grape seedlings to promote the growth and development of the grape industry in saline and alkaline areas.

The Glycine soja cytochrome P450 gene GsCYP82C4 confers alkaline tolerance by promoting reactive oxygen species scavenging.

Recent studies have demonstrated the crucial role of Cytochrome P450 enzymes (CYPs) in the production of secondary metabolites, phytohormones and antioxidants in plants. However, their functional characterization specifically under alkaline stress remains elusive. CYP82C4 was the key gene screened from a family of wild soybean CYPs in our previous studies. The aim of this present study was to clone the Glycine soja GsCYP82C4 gene and characterize its functions in Arabidopsis and Glycine max. The results showed that the GsCYP82C4 gene displayed a high expression in different plant tissues at mature stages compared to young stages. Further, higher temporal expression of the GsCYP82C4 gene was noted at 6, 12 and 24 h time points after alkali treatment in leaves compared to roots. In addition, overexpression of GsCYP82C4 improved alkaline stress tolerance in Arabidopsis via increased root lengths and fresh biomass and strengthened the antioxidant defense system via a reduction in superoxide radicals in transgenic lines compared to wild type (WT) and atcyp82c4 mutants. Further, the expression levels of stress-related marker genes were up-regulated in GsCYP82C4 OX lines under alkali stress. The functional analysis of GsCYP82C4 overexpression in soybean displayed better hairy root growth, increased fresh weight, higher antioxidant enzyme activities and reduced lipid peroxidation rates in OX lines compared to the soybean WT (K599) line. In total, our study displayed positive roles of GsCYP82C4 overexpression in both Arabidopsis and Glycine max to alleviate alkaline stress via altering expression abundance of stress responsive genes, stronger roots, higher antioxidant enzyme activities as well as reduced rates of lipid peroxidation and superoxide radicals.

Designing salt stress-resilient crops: Current progress and future challenges.

Excess soil salinity affects large regions of land and is a major hindrance to crop production worldwide. Therefore, understanding the molecular mechanisms of plant salt tolerance has scientific importance and practical significance. In recent decades, studies have characterized hundreds of genes associated with plant responses to salt stress in different plant species. These studies have substantially advanced our molecular and genetic understanding of salt tolerance in plants and have introduced an era of molecular design breeding of salt-tolerant crops. This review summarizes our current knowledge of plant salt tolerance, emphasizing advances in elucidating the molecular mechanisms of osmotic stress tolerance, salt-ion transport and compartmentalization, oxidative stress tolerance, alkaline stress tolerance, and the trade-off between growth and salt tolerance. We also examine recent advances in understanding natural variation in the salt tolerance of crops and discuss possible strategies and challenges for designing salt stress-resilient crops. We focus on the model plant Arabidopsis (Arabidopsis thaliana) and the four most-studied crops: rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), and soybean (Glycine max).

Improving Alkaline Stress Tolerance in Maize through Seed Priming with Silicon Nanoparticles: A Comprehensive Investigation of Growth, Photosynthetic Pigments, Antioxidants, and Ion Balance

Improving Alkaline Stress Tolerance in Maize through Seed Priming with Silicon Nanoparticles: A Comprehensive Investigation of Growth, Photosynthetic Pigments, Antioxidants, and Ion Balance

Enhancement of sulfur metabolism and antioxidant machinery confers Bacillus sp. Jrh14-10–induced alkaline stress tolerance in plant

Alkaline stress is a major environmental challenge that restricts plant growth and agricultural productivity worldwide. Plant growth-promoting rhizobacteria (PGPR) can be used to effectively enhance plant abiotic stress in an environment-friendly manner. However, PGPR that can enhance alkalinity tolerance are not well-studied and the mechanisms by which they exert beneficial effects remain elusive. In this study, we isolated Jrh14-10from the rhizosphere soil of halophyte Halerpestes cymbalaria (Pursh) Green and found that it can produce indole-3-acetic acid (IAA) and siderophore. By 16S rRNA gene sequencing, it was classified as Bacillus licheniformis. Inoculation Arabidopsis seedlings with Jrh14-10 significantly increased the total fresh weight (by 148.1%), primary root elongation (by 1121.7%), and lateral root number (by 108.8%) under alkaline stress. RNA-Seq analysis showed that 3389 genes were up-regulated by inoculation under alkaline stress and they were associated with sulfur metabolism, photosynthetic system, and oxidative stress response. Significantly, the levels of Cys and GSH were increased by 144.3% and 48.7%, respectively, in the inoculation group compared to the control under alkaline stress. Furthermore, Jrh14-10 markedly enhanced the activities of antioxidant enzymes, resulting in lower levels of O2•–, H2O2, and MDA as well as higher levels of Fv/Fm in alkaline-treated seedlings. In summary, Jrh14-10 can improve alkaline stress resistance in seedlings which was accompanied by an increase in sulfur metabolism-mediated GSH synthesis and antioxidant enzyme activities. These results provide a mechanistic understanding of the interactions between a beneficial bacterial strain and plants under alkaline stress.

GhIMP10D, an inositol monophosphates family gene, enhances ascorbic acid and antioxidant enzyme activities to confer alkaline tolerance in Gossypium hirsutum L.

BackgroundInositol monophosphates (IMP) are key enzymes in the ascorbic acid (AsA) synthesis pathways, which play vital roles in regulating plant growth and development and stresses tolerance. To date, no comprehensive analysis of the expression profile of IMP genes and their functions under abiotic stress in cotton has been reported.ResultsIn this study, the genetic characteristics, phylogenetic evolution, cis-acting elements and expression patterns of IMP gene family in cotton were systematically analyzed. A total of 28, 27, 13 and 13 IMP genes were identified in Gossypium hirsutum (G. hirsutum), Gossypium barbadense (G. barbadense), Gossypium arboreum (G. arboreum), and Gossypium raimondii (G. raimondii), respectively. Phylogenetic analysis showed that IMP family genes could cluster into 3 clades. Structure analysis of genes showed that GhIMP genes from the same subgroup had similar genetic structure and exon number. And most GhIMP family members contained hormone-related elements (abscisic acid response element, MeJA response element, gibberellin response element) and stress-related elements (low temperature response element, defense and stress response element, wound response element). After exogenous application of abscisic acid (ABA), some GhIMP genes containing ABA response elements positively responded to alkaline stress, indicating that ABA response elements played an important role in response to alkaline stress. qRT-PCR showed that most of GhIMP genes responded positively to alkaline stress, and GhIMP10D significantly upregulated under alkaline stress, with the highest up-regulated expression level. Virus-induced gene silencing (VIGS) experiment showed that compared with 156 plants, MDA content of pYL156:GhIMP10D plants increased significantly, while POD, SOD, chlorophyII and AsA content decreased significantly.ConclusionsThis study provides a thorough overview of the IMP gene family and presents a new perspective on the evolution of this gene family. In particular, some IMP genes may be involved in alkaline stress tolerance regulation, and GhIMP10D showed high expression levels in leaves, stems and roots under alkaline stress, and preliminary functional verification of GhIMP10D gene suggested that it may regulate tolerance to alkaline stress by regulating the activity of antioxidant enzymes and the content of AsA. This study contributes to the subsequent broader discussion of the structure and alkaline resistance of IMP genes in cotton.

OsSAP6 Positively Regulates Soda Saline–Alkaline Stress Tolerance in Rice

BackgroundSoil salinization is a worldwide environmental problem, especially in the arid and semiarid regions of northeastern China, which are heavily affected by soda saline–alkaline stress. At present, there is an urgent need to improve the soda saline–alkaline stress tolerance of rice.ResultsStress-associated proteins are involved in regulating the abiotic stresses in plants. There are 18 members of the rice stress-associated protein (OsSAP) gene family. In this study, the expression levels of OsSAP6 in leaves and roots were upregulated with increasing NaHCO3 stress duration. OsSAP6 was located in nucleus and cytoplasm. The bud length and total root length of OsSAP6 overexpression rice were significantly longer than those of Lj11 (Oryza sativa longjing11) during germination stage, and the survival rates, plant height and malondialdehyde content at the seedling stage showed tolerance growth of saline–alkaline stress. The expression of OsCu/Zn-SOD, OsAPX2, and OsCAT1 in transgenic lines was increased significantly under SAE (soda saline–alkali soil eluent) stress. OsSAP6 interacts with OsPK5 according to yeast two-hybrid screening and luciferase complementation experiments. The expression of OsPK5 increased under NaHCO3 and H2O2 stress, and the overexpression of OsPK5 in rice improved soda saline–alkaline tolerance.ConclusionOverexpression of OsSAP6 in rice significantly enhanced saline–alkaline tolerance compared with the wild type. It is speculated that OsSAP6 responds to soda salinity stress and interacts with OsPK5 to positively regulate soda saline–alkaline tolerance through ROS homeostasis. This study revealed the features of OsSAP6 involved in response to soda saline–alkaline stress and the interaction with OsPK5, which provided resources for breeding aimed at improving the soda saline–alkaline stress tolerance of rice.

IAA Plays an Important Role in Alkaline Stress Tolerance by Modulating Root Development and ROS Detoxifying Systems in Rice Plants

Auxin regulates plant growth and development, as well as helps plants to survive abiotic stresses, but the effects of auxin on the growth of alkaline-stressed rice and the underlying molecular and physiological mechanisms remain unknown. Through exogenous application of IAA/TIBA, this study explored the physiological and molecular mechanisms of alkaline stress tolerance enhancement using two rice genotypes. Alkaline stress was observed to damage the plant growth, while exogenous application of IAA mitigates the alkaline-stress-induce inhibition of plant growth. After application of exogenous IAA to alkaline-stressed rice, dry shoot biomass, foliar chlorophyll content, photosynthetic rate in the two rice genotypes increased by 12.6-15.6%, 11.7-40.3%, 51.4-106.6%, respectively. The adventitious root number, root surface area, total root length and dry root biomass in the two rice genotypes increased by 29.3-33.3%, 26.4-27.2%, 42.5-35.5% and 12.8-33.1%, respectively. The accumulation of H2O2, MAD were significantly decreased with the application of IAA. The activities of CAT, POD, and SOD in rice plants were significantly increased by exogenous application of IAA. The expression levels of genes controlling IAA biosynthesis and transport were significantly increased, while there were no significant effects on the gene expression that controlled IAA catabolism. These results showed that exogenous application of IAA could mitigate the alkaline-stress-induced inhibition of plant growth by regulating the reactive oxygen species scavenging system, root development and expression of gene involved in IAA biosynthesis, transport and catabolism. These results provide a new direction and empirical basis for improving crop alkaline tolerance with exogenous application of IAA.

Heterologous overexpression of HIOMT alleviates alkaline stress in apple plants by increasing melatonin concentration

Melatonin is an indole derivative of tryptophan that has an important function in alleviating abiotic stress. Previous studies have reported that exogenous melatonin increases the tolerance of plants to saline-alkali stress in a concentration-dependent manner, but the role of endogenous melatonin metabolism in the response of apple (Malus domestica) plants to alkali stress is unclear. In this study, the human melatonin biosynthesis-related enzyme N-acetyl-5-hydroxytryptamine methyltransferase gene (HIOMT) transformed in ‘GL-3’ apple was used to study the regulation of HIOMT in alkaline stress of apple plants. The heterologous overexpression of HIOMT under alkaline stress increased the concentration of endogenous melatonin in apple leaves, alleviated the stress-induced growth inhibition of the plants, enhanced root development, leaf photosynthesis, and antioxidant capacity, and stabilized cell membrane permeability and ionic balance. In addition, the transgenic lines also increased the concentrations of organic acids, such as oxalic acid, malic acid, malonic acid, citric acid, and succinic acid, which alleviated the high pH stress. These results provide evidence for the critical role of heterologous overexpression of HIOMT in the alkaline stress tolerance of apple plants.

GWAS and RNA-seq analysis uncover candidate genes associated with alkaline stress tolerance in maize (Zea mays L.) seedlings.

Soil salt-alkalization is a common yet critical environmental stress factor for plant growth and development. Discovering and exploiting genes associated with alkaline tolerance in maize (Zea mays L.) is helpful for improving alkaline resistance. Here, an association panel consisting of 200 maize lines was used to identify the genetic loci responsible for alkaline tolerance-related traits in maize seedlings. A total of nine single-nucleotide polymorphisms (SNPs) and their associated candidate genes were found to be significantly associated with alkaline tolerance using a genome-wide association study (GWAS). An additional 200 genes were identified when the screen was extended to include a linkage disequilibrium (LD) decay distance of r2 ≥ 0.2 from the SNPs. RNA-sequencing (RNA-seq) analysis was then conducted to confirm the linkage between the candidate genes and alkali tolerance. From these data, a total of five differentially expressed genes (DEGs; |log2FC| ≥ 0.585, p < 0.05) were verified as the hub genes involved in alkaline tolerance. Subsequently, two candidate genes, Zm00001d038250 and Zm00001d001960, were verified to affect the alkaline tolerance of maize seedlings by qRT-PCR analysis. These genes were putatively involved protein binding and “flavonoid biosynthesis process,” respectively, based on Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses. Gene promoter region contains elements related to stress and metabolism. The results of this study will help further elucidate the mechanisms of alkaline tolerance in maize, which will provide the groundwork for future breeding projects.

Insights into the Role of Iron Supplementation in Conferring Bicarbonate-Mediated Alkaline Stress Tolerance in Maize

Insights into the Role of Iron Supplementation in Conferring Bicarbonate-Mediated Alkaline Stress Tolerance in Maize

Exogenous Melatonin Alleviates Alkaline Stress by Removing Reactive Oxygen Species and Promoting Antioxidant Defence in Rice Seedlings.

Saline-alkali stress seriously restricts rice growth, development, and production in northern China. The damage of alkaline stress on rice is much greater than that of salt due to ion toxicity, osmotic stress, and especially high pH. As a signal molecule, melatonin (N-acetyl-5-methoxytryptamine, MT) mediates many physiological processes in rice and participates in protecting rice from abiotic stress. The potential mechanism of exogenous melatonin-mediated alkaline stress tolerance is still largely unknown. In this study, the effects of melatonin on the morphological change, physiological property, and corresponding genes expression in rice seedlings were analyzed under alkaline stress (20 mmol L−1, pH 9.55). The results showed that the expression levels of MT synthesis genes (TDC2, T5H, SNAT, ASMT1, and ASMT2) were induced by both exogenous MT and alkaline stress treatment. The cell membrane was protected by MT, and the MT furtherly play role in scavenging reactive oxygen species (ROS), reducing lipoxygenase (LOX) activity, and malondialdehyde (MDA) content. The scavenging of ROS by melatonin is attributed to the coupling of the improvement of redox homeostasis and the enhancement of antioxidant enzyme activity and antioxidant content by upregulating the transcriptional levels of antioxidase genes. In the meantime, MT pretreatment promoted the accumulation of free proline, sucrose, and fructose by regulating the OsP5CS, OsSUS7, and OsSPS1 gene expression level and increased chlorophyll content upregulating the expression of chlorophyll synthesis-related genes. Ultimately, the alleviating effect of exogenous melatonin on alkaline stress was reflected in increasing the leaf relative water content (RWC) and root-shoot ratio and reducing the leaf tip wilt index (TWI) through a series of physiological and biochemical changes. Melatonin pretreatment changed the expression level of MT synthesis genes which might contribute to MT synthesis in rice, consequently, activated the ROS scavenging system and alleviating the damage of alkaline stress on rice seedlings. Our study comprehensively understands the alleviating effect of exogenous melatonin on rice under alkaline stress.

Genotyping of Listeria monocytogenes strains in Italian food-processing environments

Abstract Background In 2019, case fatality from Listeria monocytogenes (Lm) was higher than the previous years confirming Lm as a major public health problem. Food is the main source of Lm infection and cross-contamination from the food-processing environment (FPEs) is the most common route of contamination. The aim of this work was to characterize FPEs Lm strains collected from the National Reference Laboratory (NRL) for Lm in order to evaluate circulating clonal complexes (CCs) and their environmental adaptation. Methods NRL Lm database actually consists of 798 FPEs sequenced strains. In silico MLST was evaluated. Sequences related to prevalent CCs were further investigated using Pasteur's cgMLST scheme and detecting metal and detergent resistance genes and stress survival islet (SSI). Results MLST identified 25 CCs and 4 singleton. Nine isolates gave inexact match with existing alleles and were not classified. CC9 (17.4%) and CC121 (14.2%) were the prevalent clones. CC9 cgMLST analysis revealed a relatedness among strains isolated from the same establishment type (meat or dairy), even if sampled in different regions. Indeed, CC121 cgMLST clustering analysis was strictly associated to the point of sampling. Regarding stress adaptation genes, SSI1 and brcABC genes were detected in 100% and 2.9% of the CC9 strains, respectively. Meanwhile, SSI2 and transposon Tn6188 were detected, respectively, in 100% and 97.3% of CC121 strains. Conclusions Results confirmed, in Italian FPEs, prevalence of hypovirulent Lm strains, as previously observed in Italian food. Tested isolates highlighted adaptation to low pH and high salt concentration (SSI1 genes for CC9), to alkaline and oxidative stress (SSI2 genes for CC121) and benzalkonium chloride tolerance (Tn6188 in CC121) resulting in a best survival under stress conditions. Interestingly, CC9 clustering denoted allelic proximity among strains isolated in different Italian regions paying attention to clones spreading at national level. Key messages Listeria monocytogenes CC9 and CC121 prevalence in Italian establishment confirms environment is the main route of food contamination at production level. Prevalent food-processing environmental Italian Listeria monocytogenes strains denotes adaptation to environmental stress and clones spreading at national level.

SET DOMAIN GROUP 721 protein functions in saline-alkaline stress tolerance in the model rice variety Kitaake.

To isolate the genetic locus responsible for saline–alkaline stress tolerance, we developed a high‐throughput activation tagging‐based T‐DNA insertion mutagenesis method using the model rice (Oryza sativa L.) variety Kitaake. One of the activation‐tagged insertion lines, activation tagging 7 (AC7), showed increased tolerance to saline–alkaline stress. This phenotype resulted from the overexpression of a gene that encodes a SET DOMAIN GROUP 721 protein with H3K4 methyltransferase activity. Transgenic plants overexpressing OsSDG721 showed saline–alkaline stress‐tolerant phenotypes, along with increased leaf angle, advanced heading and ripening dates. By contrast, ossdg721 loss‐of‐function mutants showed increased sensitivity to saline–alkaline stress characterized by decreased survival rates and reduction in plant height, grain size, grain weight and leaf angle. RNA sequencing (RNA‐seq) analysis of wild‐type Kitaake and ossdg721 mutants indicated that OsSDG721 positively regulates the expression level of HIGH‐AFFINITY POTASSIUM (K+ ) TRANSPORTER1;5 (OsHKT1;5), which encodes a Na+‐selective transporter that maintains K+/Na+ homeostasis under salt stress. Furthermore, we showed that OsSDG721 binds to and deposits the H3K4me3 mark in the promoter and coding region of OsHKT1;5, thereby upregulating OsHKT1;5 expression under saline–alkaline stress. Overall, by generating Kitaake activation‐tagging pools, we established that the H3K4 methyltransferase OsSDG721 enhances saline–alkaline stress tolerance in rice.

Transcriptional profiling of alkaline stress-induced defense responses in soybean (Glycine max)

Alkaline stress has been considered a major environmental threat to plant growth and agricultural production. Even though the mechanisms have been characterized in some plants, the information about the alkaline stress-induced defense responses in soybean is insufficient. To identify defense related genes, the transcriptional profiles of soybean seedlings were examined using RNA sequencing under alkaline stress. The results showed that a total of 4603 genes were up-regulated and 1659 were down-regulated compared to expression in control plants. Further, the functional enrichment analysis showed that these differentially expressed genes were significantly enriched in 43 pathways and mainly associated with catalytic activity and binding, metabolic process, cellular process and cell progress. Then, 19 transcription factors from AP2-EREBF, MYB families and isoflavone related genes were chosen and identified to be induced under alkaline stress by quantitative real-time polymerase chain reaction (qRT-PCR). Taken together, our results highlight the differentially expressed genes and identify a set of genes associated with the response to alkaline stress, which findings establish a foundation for further analyses of soybean alkaline stress tolerance mechanisms. Supplemental data for this article is available online at https://doi.org/10.1080/13102818.2021.1976078 .

F-box only and CUE proteins are crucial ubiquitination-associated components for conidiation and pathogenicity in the rice blast fungus, Magnaporthe oryzae

Ubiquitination, an important process in post-translational modification, regulates various mechanisms in eukaryotes including protein degradation and interaction, cell cycle, stress response, and pathogenicity. The Skp1/Cullin/F-box and the endoplasmic reticulum-associated degradation (ERAD) complexes, RING E3 ligase complexes, are involved in ubiquitin-mediated proteolysis and protein quality control. The F-box protein has FBXO (F-box only or others), FBXW (with WD40), and FBXL (with LRR) classes depending on which interaction domain is present on the C-terminus. The ubiquitin system component cue (CUE) protein is a key factor of ERAD. However, the biological roles of FBXO and CUE proteins are largely unknown in plant pathogenic fungi including Magnaporthe oryzae. To elucidate the roles of FBXO and CUE proteins in fungal development and pathogenicity, MoFBX15 and MoCUE1 were functionally characterized in M. oryzae. Two ubiquitination-associated genes were crucial for conidiation, alkaline stress tolerance, and pathogenicity in M. oryzae. In particular, MoCUE1 was important for ER stress response and localization and translocation of cytoplasmic effectors. Moreover, ubiquitination and SUMOylation levels were decreased and transcript levels of deSUMOylation-associated genes were increased in ΔMofbx15 and ΔMocue1. This study will provide not only comprehensive understanding of the role of ubiquitination but also new insights on crosstalk between ubiquitination and SUMOylation in rice blast fungus and other fungal pathogens.

Small RNA Sequencing in Sugar Beet Under Alkaline Stress

MiRNAs have been proved to participate in the abiotic stress responses in plants. Sugar beet can adapt itself to different abiotic stresses, in particular the alkaline and salinity stresses. Nonetheless, the number, features, sequences and possible effects of miRNAs on the plant responses to alkaline stress remain largely unclear. Small RNA sequencing was carried out in sugar beet cultivar KWS0143 seedling leaves under alkaline solution treatments for 0 (control, C), 3 (short term, ST) as well as 7 (long term, LT) days, respectively. As a result, the RNAs 24 nt in length showed the highest abundance among three sugar beet libraries, followed by those 21 nt and 22 nt in length. Besides, among these three libraries, a total of 2134 miRNAs were identified, which belonged to 47 families. Each of identified known miRNA showed high conservation level among different plant species. 24 novel miRNAs were also identified that possessed standard miRNA* sequences and hairpin precursors, with the length of 20–24 nt. Expression of 222 miRNAs was detected under each treatment, including 169 known and 53 novel miRNAs. Sixteen miRNAs showed specific expression in ST treatment, while twenty-nine showed expression in LT treatment. Besides, we estimated 45 characteristic coding genes as the targets for 67 alkali-responsive miRNAs. According to GO analysis, numerous target genes of differentially expressed miRNAs (DEmiRNAs) showed enrichment into the “redox process,” such as polyphenol oxidase gene LOC04900758. Our results provided a valuable resource on alkali-responsive miRNAs and should benefit the improvement in alkaline stress tolerance in sugar beet.

Transcriptome analysis of sugar beet (Beta vulgaris L.) in response to alkaline stress.

RNA-seq was used to analyze the transcriptional changes in sugar beet (Beta vulgaris L.) triggered by alkaline solution to elucidate the molecular mechanism underlying alkaline tolerance in sugar beet. Several differentially expressed genes related to stress tolerance were identified. Our results provide a valuable resource for the breeding of new germplasms with high alkaline tolerance. Alkalinity is a highly stressful environmental factor that limits plant growth and production. Sugar beet own the ability to acclimate to various abiotic stresses, especially salt and alkaline stress. Although substantial previous studies on response of sugar beet to saline stress has been conducted, the expressions of alkali-responsive genes in sugar beet have not been comprehensively investigated. In this study, we conducted transcriptome analysis of leaves in sugar beet seedlings treated with alkaline solutions for 0day (control, C), 3days (short-term alkaline treatment, ST) and 7days (long-term alkaline treatment, LT). The clean reads were obtained and assembled into 25,507 unigenes. Among them, 975 and 383 differentially expressed genes (DEGs) were identified in the comparison groups ST_vs_C and LT_vs_C, respectively. Gene ontology (GO) analysis revealed that oxidation-reduction process and lipid metabolic process were the most enriched GO term among the DEGs in ST_vs_C and LT_vs_C, respectively. According to Kyoto Encyclopedia of Genes and Genomes pathway, carbon fixation in photosynthetic organisms pathway were significantly enriched under alkaline stress. Besides, expression level of genes encoding D-3-phosphoglycerate dehydrogenase 1, glutamyl-tRNA reductase 1, fatty acid hydroperoxide lyase, ethylene-insensitive protein 2, metal tolerance protein 11 and magnesium-chelatase subunit ChlI, etc., were significantly altered under alkaline stress. Additionally, among the DEGs, 136 were non-annotated genes and 24 occurred with differential alternative splicing. Our results provide a valuable resource on alkali-responsive genes and should benefit the improvement of alkaline stress tolerance in sugar beet.

Silicon and salicylic acid confer high-pH stress tolerance in tomato seedlings

Alkalinity is a known threat to crop plant growth and production, yet the role of exogenous silicon (Si) and salicylic acid (SA) application has been largely unexplored. Here, we sought to understand the beneficial impacts of Si and SA on tomato seedlings during high-pH (9.0) stress. Results showed that Si- and SA-treated plants displayed higher biomass, chlorophyll contents, relative leaf water and better root system than none-treated plants under alkaline conditions. Both Si and SA counteracted the alkaline stress-induced oxidative damage by lowering the accumulation of reactive oxygen species and lipid peroxidation. The major antioxidant defence enzyme activities were largely stimulated by Si and SA, and these treatments caused significantly increased K+ and lowered Na+ concentrations in shoot and root under stress. Moreover, Si and SA treatments modulated endogenous SA levels and dramatically decreased abscisic acid levels in both shoot and root. Additionally, key genes involved in Si uptake, SA biosynthesis, the antioxidant defence system and rhizosphere acidification were up-regulated in Si and SA treatments under alkaline conditions. These results demonstrate that Si and SA play critical roles in improving alkaline stress tolerance in tomato seedlings, by modifying the endogenous Na+ and K+ contents, regulating oxidative damage and key genes and modulating endogenous hormone levels. These findings will help to broaden our understanding regarding the physiological and molecular mechanisms associated with the alkaline soil tolerance in plants.