OBJECTIVES: This study aims to investigate the impact of glutathione S-transferase (GST) on the environmental adaptability of Streptococcus mutans (S. mutans). METHODS: A GST knockout strain ΔgsT was constructed. Transcriptomic sequencing was performed to analyze the gene expression differences between the wild-type S. mutans UA159 and its GST knockout strain ΔgsT. Comprehensive functional assessments, including acid tolerance assays, hydrogen peroxide challenge assays, nutrient limitation growth assays, and fluorescence in situ hybridization, were conducted to evaluate the acid tolerance, antioxidant stress resistance, growth kinetics, and interspecies competitive ability of ΔgsT within plaque biofilms. RESULTS: Compared with the wild-type S. mutans, 198 genes in ΔgsT were significantly differentially expressed and enriched in pathways related to metabolism, stress response, and energy homeostasis. The survival rate of ΔgsT in acid tolerance assays was markedly reduced (P<0.01). After 15 min of hydrogen peroxide challenge, the survival rate of ΔgsT decreased to 38.12% (wild type, 71.75%). Under nutrient-limiting conditions, ΔgsT exhibited a significantly lower final OD₆₀₀ value than the wild-type strain (P<0.05). In the biofilm competition assays, the proportion of S. mutans ΔgsT in the mixed biofilm (8.50%) was significantly lower than that of the wild type (16.89%) (P<0.05). CONCLUSIONS GST enhances the acid resistance, oxidative stress tolerance, and nutrient adaptation of S. mutans by regulating metabolism-related and stress response-related genes.
Streptococcus mutans/enzymology* ; Biofilms ; Glutathione Transferase/physiology* ; Adaptation, Physiological ; Hydrogen Peroxide/pharmacology* ; Gene Expression Regulation, Bacterial ; Oxidative Stress ; Metabolic Reprogramming

The HDAs (a subfamily of histone deacetylases), a class of Zn²⁺-dependent histone deacetylases, are highly homologous to the reduced potassium dependency 3 (RPD3) in yeast. HDAs extensively regulate chromosome stability, gene transcription, and protein activity by catalyzing the removal of acetyl group from histone and non-histone lysine residues. HDA-mediated deacetylation is essential for plant growth, development, and responses to abiotic stress. We review the research progress in HDAs regarding the discovery, structures, classification, deacetylation process, and roles in regulating plant responses to abiotic stress. Furthermore, this paper prospects the future research on HDAs, aiming to provide theoretical support for the research on epigenetic regulation mediated by HDAs.
Histone Deacetylases/classification* ; Zinc/metabolism* ; Stress, Physiological/physiology* ; Plants/genetics*

Autophagy is an evolutionarily conserved self-degradation process in eukaryotes. It not only plays a role in plant growth and development but also is involved in plant responses to biotic and abiotic stresses. Plants can initiate autophagy to degrade the surplus or damaged cytoplasmic materials and organelles, thus coping with abiotic and biotic stresses. The initiation of autophagy depends on autophagy-related genes (ATGs). The transcription factors can directly bind to the promoters of ATGs to activate autophagy and regulate their transcriptional levels and post-translational modifications. Furthermore, ATGs can directly or indirectly interact with plant hormones to regulate plant responses to stresses. When plants are exposed to salinity, drought, extreme temperatures, nutrient deficiencies, and pathogen stress, ATGs are significantly induced, which enhances the autophagy activity to facilitate the degradation of the denatured and misfolded proteins, thereby enhancing plant tolerance to adversity stresses. This article summarizes the discovery, structures, and classification of plant ATGs, reviews the research progress in the mechanisms of ATGs in plant responses to abiotic and biotic stresses, and prospects the future research directions. This review is expected to provide the genetic resources and a theoretical foundation for the genetic improvement of crops in responses to stress tolerance.
Autophagy/physiology* ; Stress, Physiological/genetics* ; Gene Expression Regulation, Plant ; Plants/metabolism* ; Transcription Factors/metabolism* ; Plant Proteins/genetics* ; Genes, Plant ; Plant Physiological Phenomena ; Droughts

Ophiopogon japonicus, a precious medicinal plant endemic to Zhejiang Province. Its tuberous roots are rich in bioactive components such as flavonoids, possessing anti-inflammatory, antioxidant, and immunomodulatory properties. To elucidate the impact of cadmium (Cd) stress on the accumulation and biosynthetic pathway of flavonoids in O. japonicus, this study exposed O. japonicus to different concentrations of Cd stress and explored the changes through integrated transcriptomics and metabolomics analysis. The results demonstrated that Cd stress (1 mg/L and 10 mg/L) significantly increased the content of flavonoids in O. japonicus in a concentration-dependent manner. The metabolomics analysis revealed a total of 110 flavonoids including flavones, flavanols, flavonols, flavone and flavonol derivatives, flavanones, isoflavonoids, chalcones and dihydrochalcones, and anthocyanins in O. japonicus, among which flavones, flavonols, flavone and flavonol derivatives, and anthocyanins increased under Cd stress. The transcriptomics analysis identified several key flavonoid biosynthesis-associated genes with up-regulated expression under Cd stress, including 14 genes encoding 4-coumarate CoA ligase (4CL), 2 genes encoding chalcone isomerase (CHI), and 14 genes encoding phenylalanine ammonia lyase (PAL). The gene-metabolite regulatory network indicated significant positive correlations of 4CL (Cluster-21637.5012, Cluster-21637.90648, and Cluster-21637.62637) and CHI (Cluster-21637.111909 and Cluster-21637.123300) with flavonoid metabolites, suggesting that these genes promoted the synthesis of specific flavonoid metabolites, which led to the accumulation of total flavonoids under Cd stress. These findings provide theoretical support for the cultivation and utilization of medicinal plants in Cd-contaminated environments and offered new perspectives for studying plant responses to heavy metal stress.
Cadmium/toxicity* ; Flavonoids/biosynthesis* ; Metabolomics ; Ophiopogon/drug effects* ; Stress, Physiological ; Transcriptome ; Gene Expression Profiling ; Gene Expression Regulation, Plant

Prunus mume is an ecologically and economically valuable plant with both medicinal and edible values. However, drought severely limits the promotion and cultivation of P. mume in the arid and semi-arid areas in northern China. In this study, we treated P. mume 'Meiren' with natural drought and then assessed photosynthetic and physiological indexes such as osmoregulatory substances, photosynthetic parameters, and antioxidant enzyme activities. Furthermore, we employed transcriptome sequencing to explore the internal regulatory mechanism of P. mume under drought stress. As the drought stress aggravated, the levels of chlorophyll a (Chla), chlorophyll b (Chlb), chlorophyll (a+b)[Chl(a+b)], and soluble protein (SP) in P. mume first elevated and then declined. The net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum photochemical efficiency (Fv/Fm), effective photochemical quantum yield [Y(Ⅱ)], photochemical quenching (qP), and relative electron transport rate (ETR) all kept decreasing, while the levels of malondialdehyde, superoxide dismutase (SOD), peroxidase (POD), and osmoregulatory substances rose. Transcriptome sequencing revealed a total of 24 853 high-quality genes. Gene ontology (GO) enrichment showed that differentially expressed genes (DEGs) were the most under severe drought. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis showed that the DEGs during the four drought periods were mainly involved in the biosynthesis of secondary metabolites, plant-pathogen interaction, plant hormone signal transduction, starch and sucrose metabolism, and mitogen-activated protein kinase signaling pathways. Furthermore, we identified 16 key genes associated with the drought tolerance of P. mume 'Meiren'. This study discovered that P. mume might up-regulate or down-regulate the expression of drought tolerance-related genes such as SUS, P5CS, LEA, SOD, POD, SOD1, TPPD, and TPPA via transcription factors like MYB, ERF, bHLH, NAC, and WRKY to promote the accumulation of osmoregulatory substances like sucrose and enhance the activities of antioxidant enzymes such as SOD and POD, thus reducing the harm of reactive oxygen species and protecting the structure and function of the membrane system under drought stress. The findings provide theoretical references for further exploration of candidate genes of P. mume in response to drought stress and breeding of drought-tolerant varieties.
Droughts ; Photosynthesis/physiology* ; Gene Expression Regulation, Plant ; Stress, Physiological/genetics* ; Prunus/genetics* ; Chlorophyll/metabolism* ; Plant Proteins/genetics*

Soil cadmium pollution can adversely affect the cultivation of the ornamental plant, Coleus scutellarioides. Upon cadmium contamination of the soil, the growth of C. scutellarioides is impeded, and it may even succumb to the toxic accumulation of cadmium. In this study, we investigated the effects of arbuscular mycorrhizal fungi (AMF) on the adaptation of C. scutellarioides to cadmium stress, by measuring the physiological metabolism and the degree of root damage of C. scutellarioides, with Aspergillus oryzae as the test fungi. The results indicated that cadmium stress increased the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and the content of malondialdehyde (MDA) and proline (Pro) within the cells of C. scutellarioides, but inhibited mycorrhizal infestation rate, root vigour and growth rate to a great degree. With the same cadmium concentration, the inoculation of AMF significantly improved the physiological indexes of C. scutellarioides. The maximum decrease of MDA content was 42.16%, and the content of secondary metabolites rosemarinic acid and anthocyanosides could be increased by up to 27.43% and 25.72%, respectively. Meanwhile, the increase of root vigour was as high as 35.35%, and the DNA damage of the root system was obviously repaired. In conclusion, the inoculation of AMF can promote the accumulation of secondary metabolites, alleviate root damage, and enhance the tolerance to cadmium stress in C. scutellarioides.
Cadmium/toxicity* ; Mycorrhizae/physiology* ; Plant Roots/drug effects* ; Soil Pollutants/toxicity* ; Stress, Physiological ; Superoxide Dismutase/metabolism*

Beta-amylases (BAMs), key enzymes in starch hydrolysis, play an important role in plant growth, development, and resistance to abiotic stress. To mine the saline-alkali tolerance-related BAM genes in alfalfa (Medicago sativa L.), we identified MsBAM genes in the whole genome. The physicochemical properties, phylogeny, gene structures, conserved motifs, secondary structures, promoter cis-acting elements, chromosome localization, and gene replication relationships of BAM gene family members were analyzed. RNA-seq and quantitative real-time PCR (qRT-PCR) were employed to analyze the expression patterns of BAM family members under saline-alkali stress. The results showed that 54 BAM genes were identified in the genome, which were classified into 8 subgroups according to the phylogenetic tree. The members of the same subgroup had similar gene structures except that those of subgroups 1 and 7 had large differences. Conserved motif analysis showed that all MsBAM proteins had a typical glycohydrolysis domain. The chromosome localization analysis showed that MsBAM gene family members were unevenly distributed on 27 chromosomes. The duplication of gene segments led to the increase in BAM gene number in alfalfa. The promoters of BAM genes contained a large number of elements in response to plant hormones and stress. Transcriptome data and qRT-PCR results showed that the expression levels of most MsBAM genes were up-regulated in response to saline-alkali stress. Under the saline-alkali stress, the expression levels of 28 genes, including MsBAM6, were up-regulated on days 1 and 7, and those of 5 genes, including MsBAM9, were up-regulated by over 2 folds. In addition, under salt-alkali stress, BAM activity and soluble sugar content were significantly increased. These results indicate that BAM genes play a key role in alfalfa in response to saline-alkali stress, laying a foundation for further research in this field.
Medicago sativa/physiology* ; beta-Amylase/metabolism* ; Phylogeny ; Gene Expression Regulation, Plant ; Stress, Physiological/genetics* ; Multigene Family ; Alkalies ; Plant Proteins/genetics*

Soil cadmium (Cd) pollution is one of the major environmental problems globally. Ophiopogon japonicus, a multifunctional plant extensively used in traditional Chinese medicine, has demonstrated potential in environmental remediation. This study investigated the Cd accumulation pattern of O. japonicus under cadmium stress and identified the heavy metal ATPase (HMA) family members in this plant. Our results demonstrated that O. japonicus exhibited a Cd enrichment factor (EF) of 2.75, demonstrating strong potential for soil Cd pollution remediation. Nine heavy metal ATPase (HMA) members of P1B-ATPases were successfully identified from the transcriptome data of O. japonicus, with OjHMA1-OjHMA6 classified as the Zn/Co/Cd/Pb-ATPases and OjHMA7-OjHMA9 as the Cu/Ag-ATPases. The expression levels of OjHMA1, OjHMA2, OjHMA3, and OjHMA7 were significantly up-regulated under Cd stress, highlighting their crucial roles in cadmium ion absorption and transport. The topological analysis revealed that these proteins possessed characteristic transmembrane (TM) segments of the family, along with functional A, P, and N domains involved in regulating ion absorption and release. Metal ion-binding sites (M4, M5, and M6) existed on the TM segments. Based on the number of transmembrane domains and the residues at metal ion-binding sites, the plant HMA family members were categorized into three subgroups: P1B-1 ATPases, P1B-2 ATPases, and P1B-4 ATPases. Specifically, the P1B-1 ATPase subgroup included the motifs TM4(CPC), TM5(YN[X]₄P), and TM6(M[XX]SS); the P1B-2 ATPase subgroup featured the motifs TM4(CPC), TM5(K), and TM6(DKTGT); the P1B-4 ATPase subgroup contained the motifs TM4(SPC) and TM6(HE[X]GT), all of which were critical for protein functions. Molecular docking results revealed the importance of conserved sequences such as CPC/SPC, DKTGT, and HE[X]GT in metal ion coordination and stabilization. These findings provide potential molecular targets for enhancing Cd uptake and tolerance of O. japonicus by genetic engineering and lay a theoretical foundation for developing new cultivars with high Cd accumulation capacity.
Cadmium/metabolism* ; Adenosine Triphosphatases/metabolism* ; Ophiopogon/drug effects* ; Soil Pollutants/toxicity* ; Plant Proteins/metabolism* ; Stress, Physiological ; Multigene Family ; Gene Expression Regulation, Plant

Glucosidases are an indispensable class of enzymes in the sugar metabolism of organisms. To investigate the biological functions and expression patterns of α-glucosidases (AGLUs) and β-glucosidases (BGLUs), we identified the two family members in the genome of melon (Cucumis melo). The number, location on chromosomes, gene structure, subcellular localization, conserved motifs, and phylogenetic relationship of the two family members were analyzed. Based on the cis-acting elements in the promoter region and protein interaction models, their functions were preliminarily predicted. Furthermore, the gene expression of the two family members was determined by qRT-PCR. The results showed that the melon genome contained five AGLU family members on five chromosomes, and all of the five members were located in the extracellular matrix, with the amino acid sequence lengths ranging from 899 aa to 1 060 aa. The melon genome carried 18 BGLU family members on 8 chromosomes, and all the members were located in the cell membrane or cytoplasm, with the amino acid lengths ranging from 151 aa to 576 aa. The qRT-PCR results showed that the expression of about 50% of the genes was down-regulated upon cold stress. CmAGLU5 and CmBGLU7 may be key members of the two families, respectively, in response to cold stress. The expression of all members of the two families was up-regulated under abscisic acid (ABA), high salt, and drought stress. In the AGLU family, CmAGLU3 was the key gene in response to ABA and high salt stress, while CmAGLU4 was the key gene in response to drought stress. In the BGLU family, CmBGLU18 was the key gene in response to ABA, while CmBGLU6 was the key gene in response to high salt and drought stress.
beta-Glucosidase/metabolism* ; Phylogeny ; alpha-Glucosidases/metabolism* ; Gene Expression Regulation, Plant ; Cucurbitaceae/enzymology* ; Multigene Family ; Cucumis melo/enzymology* ; Stress, Physiological

Cucumber (Cucumis sativus L.) is one of the most widely cultivated vegetables in the world. High temperature and other stress conditions can affect the growth and development of this plant, even leading to the decreases in yield and quality. The mitogen-activated protein kinase (MAPK) family plays a crucial role in plant stress responses. However, the role of MPK4 in the stress response of cucumber remains to be reported. In this study, we cloned CsMPK4, which encoded 383 amino acid residues. The qRT-PCR results showed that the expression level of CsMPK4 was the highest in leaves and flowers, moderate in roots, and the lowest in stems and tendrils. CsMPK4 was located in the nucleus and cytoplasm, and it had a close relationship with CmMPK4 in muskmelon. The cucumber plants overexpressing CsMPK4 became stronger and shorter, with reduced length and quantity of tendrils. Moreover, the transgenic seedlings were more resistant to high temperatures, with decreased malondialdehyde (MDA) content and increased activities of peroxidase (POD) and superoxide dismutase (SOD) in young leaves. Furthermore, the protein-protein interaction between CsMPK4 and CsVQ10, a member of the valine-glutamine family, was confirmed by yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays. The results suggested that CsVQ10 cooperated with CsMPK4 in response to the high temperature stress in cucumber. This study laid a foundation for the further study on the stress response mechanism of CsMPK4 and the breeding of stress-resistant cucumber varieties.
Cucumis sativus/metabolism* ; Mitogen-Activated Protein Kinases/physiology* ; Plant Proteins/metabolism* ; Plants, Genetically Modified/metabolism* ; Gene Expression Regulation, Plant ; Stress, Physiological/genetics* ; Cloning, Molecular