Genome-Wide Identification of Barley ABC Genes and Their Expression in Response to Abiotic Stress Treatment

ABCB transporters: functionality extends to more than auxin transportation

MAIN CONCLUSION

ABCs transport diverse compounds; with plant's most abundant ABCG and ABCB subfamilies. ABCBs are multi-functional transporter proteins having role in plant adaptation. ATP-binding cassette (ABC) proteins have been known for the transportation of various structurally diverse compounds in all kingdoms of life. Plants possess a particularly high number of ABC transporters compared to other eukaryotes: the most abundant being ABCG followed by the ABCB subfamilies. While members of the ABCB subfamily are primarily known for auxin transportation, however, studies have shown their involvement in variety of other functions viz. growth and development, biotic and abiotic stresses, metal toxicity and homeostasis, cellular redox state stability, stomatal regulation, cell shape maintenance, and transport of secondary metabolites and phytohormones. These proteins are able to perform various biological processes due to their widespread localization in the plasma membrane, mitochondrial membrane, chloroplast, and tonoplast facilitating membrane transport influenced by various environmental and biological cues. The current review compiles published insights into the role of ABCB transporters, and also provides brief insights into the role of ABCB transporters in a medicinal plant, where the synthesis of its bioactive secondary metabolite is linked to the primary function of ABCBs, i.e., auxin transport. The review discusses ABCB subfamily members as multi-functional protein and comprehensively examines their role in various biological processes that help plants to survive under unfavorable environmental conditions.

Genome-Wide Identification, Molecular Evolution, and Expression Divergence of CLC, ALMT, VDAC, and MSL Gene Family in Barley

Organic and inorganic nutrients, osmotic components, associated protein cofactors, and signaling molecules regulate biotic and abiotic stresses in plants. Earlier reports suggest that plant cells activate anion channels and induce the efflux of anions at the plasma membrane under drought. Herein, CHLORIDE CHANNEL (CLC), ALUMINUM-ACTIVATED MALATE TRANSPORTER (ALMT), VOLTAGE-DEPENDENT ANION CHANNEL (VDAC), and MECHANOSENSITIVE CHANNEL of SMALL CONDUCTANCE-LIKE (MscS-like, MSL) gene family were reported in barley. Totally, 43 anion channel proteins were identified in barley at the genome-wide level. Expression profiles of anion channel genes were obtained from public databases and verified by qRT-PCR. In addition, the expression pattern of the anion channel gene family in multiple tissues among ten land plants showed the organs in which it is actively expressed, and 43 anion channel genes were expressed in diverse tissues, such as tillers, epidermal strips, inflorescences, and grain in barley. The expression of anion channel genes was performed in ten different cultivars and wild barley, of which 17 genes were confirmed by qRT-PCR under drought treatment, suggesting that different cultivars have diverse anion channel genes in response to drought stress. The plants with high transcripts of these genes demonstrated stronger tolerance to drought stress and element content (e.g., potassium, calcium). The results might help to further elucidate the molecular mechanism of anion channels related to stress and provide a toolkit for enhancing the drought tolerance of barley.

Transcriptome alterations related to heat stress responses of wild and cultivated barle

Heat stress, exacerbated by global warming, threatens food security by disrupting plant growth and productivity across many regions. The present study compared the transcriptome changes of heat-tolerant wild (Hordeum vulgare ssp. spontaneum L.) genotype and heat-sensitive cultivated Hordeum ('Mona' cultivar) barley subjected to control (24 ± 2 °C) and heat stress (40 ± 2 °C, 3 h) conditions via RNA sequencing with the Illumina Hiseq2500 platform. The wild barley genotype exhibited less impact from heat stress on growth and physiology than the 'Mona' cultivar. Heat stress led to 2141 differentially expressed genes (DEGs) in the heat-tolerant wild genotype and 1456 in the 'Mona' cultivar. Gene ontology enrichment analysis of the DEGs revealed that biological processes such as defense response to heat stress, proline and polyamine biosynthesis, and oxidative stress scavenging were predominantly involved in the thermo-tolerance of wild barley. Moreover, heat shock proteins, osmoprotectants, and catalytic activity were identified as the most critical molecular functions in response to high temperatures in wild barley. The significant alterations in the expression levels of candidate genes in response to heat stress highlight these genes' pivotal role in the thermo-tolerance of wild barley compared to the heat-sensitive 'Mona' cultivar. Comparing the evolved mechanisms in response to high temperatures between wild and cultivated barley helps identify the effective heat tolerance mechanisms in the thermo-tolerant wild genotype.

Comprehensive analysis of epigenetic modifications in alfalfa under cadmium stress

Epigenetics plays an important role in plant growth and development and in environmental adaptation. Alfalfa, an important forage crop, is rich in nutrients. However, little is known about the molecular regulatory mechanisms underlying the response of alfalfa to cadmium (Cd) stress. Here, we performed DNA methylation (5mC), RNA methylation (m6A) and transcriptomic sequencing analyses of alfalfa roots under Cd stress. Whole-genome methylation sequencing and transcriptomic sequencing revealed that Cd stress reduced DNA methylation levels. Moreover, a reduced 5mC methylation level was associated with decreased expression of several DNA methyltransferase genes. Compared with those under normal (CK) conditions, the m6A modification levels under Cd stress were greater and were positively correlated with gene expression in alfalfa roots. We also found a negative correlation between the 5mC level and the m6A level, especially in CG and CHG contexts. In yeast, the overexpression of MsNARMP5 (natural resistance-associated macrophage protein) and MsPCR2 (plant cadmium resistance 2), which are modified by 5mC or m6A, significantly increased Cd stress tolerance. These results provide candidate genes for future studies on the mechanism of Cd stress tolerance in alfalfa roots and valuable information for studying heavy metal stress in alfalfa breeding.

ABCG Transporters in the Adaptation of Rice to Salt Stresses

The ATP-binding cassette (ABC) proteins are a diverse family of transmembrane transporter proteins widely identified in various organisms. The ABCG transporters belong to the G subfamily of the ABC transporter family. Rarely research on ABCG transporters involved in salt tolerance of rice was found. In this study, the evolutionary relationships, conserved motifs, intra- and inter-species homologous genes, and cis-acting elements of ABCG subfamily members were analyzed, and the expression changes of these genes under salt stress at 0 h, 3 h, and 24 h were detected. Based on these results, the candidate gene OsABCG7, which is induced by salt stress, was selected for further studies. Yeast experiments confirmed that the OsABCG7 gene might be involved in the regulation of salt tolerance. The abcg7 mutant showed a higher degree of leaf wilting and a lower survival rate, exhibiting a salt-sensitive phenotype. Systematic analysis of this family in rice helps design effective functional analysis strategies and provides data support for understanding the role of ABCG transporters under salt stress.

The CDPK-related protein kinase HvCRK2 and HvCRK4 interact with HvCML32 to negatively regulate drought tolerance in transgenic Arabidopsis thaliana

Calcium-dependent protein kinase (CDPK) as one of calcium sensors were play important roles in stress responses. CDPK-related protein kinase (CRK) was identified as subgroup III of CDPK has been characterized in many plants, but the members and functions of CRK genes in hulless barley (Hordeum vulgare L.) has not been clarified. Here, we identified four HvCRK genes and named HvCRK1-4 according to chromosomes localization. Moreover, the physiological function of highly induced genes of HvCRK2 and HvCRK4 were investigated in drought stress tolerance by examining their overexpression transgenic lines functions generated in Arabidopsis thaliana. Under drought stress, both overexpression HvCRK2 and HvCRK4 displayed reduced drought resistance, and accompanied by higher accumulation levels of ROS. Notably, overexpression of HvCRK2 and HvCRK4 reduced sensitivity to exogenous ABA, meanwhile the expression of ABA-responsive genes in transgenic plants were down-regulated compared to the wild type in response to drought stress. Furthermore, the physically interaction of HvCRK2 and HvCRK4 with calmodulin (CaM) and calmodulin-like (CML) proteins were determined in vivo, the further results showed that HvCML32 binds to HvCRK2/4 S_TKC structural domains and negatively regulates drought tolerance. In summary, this study identified HvCRK members and indicated that HvCRK2 and HvCRK4 genes play negative roles in drought tolerance, and provide insight into potential molecular mechanism of HvCRK2 and HvCRK4 in response to drought stress.

Phylogenetic insight into ABCE gene subfamily in plants

ATP-BINDING CASSETTE SUBFAMILY E MEMBER (ABCE) proteins are one of the most conserved proteins across eukaryotes and archaea. Yeast and most animals possess a single ABCE gene encoding the critical translational factor ABCE1. In several plant species, including Arabidopsis thaliana and Oryza sativa, two or more ABCE gene copies have been identified, however information related to plant ABCE gene family is still missing. In this study we retrieved ABCE gene sequences of 76 plant species from public genome databases and comprehensively analyzed them with the reference to A. thaliana ABCE2 gene (AtABCE2). Using bioinformatic approach we assessed the conservation and phylogeny of plant ABCEs. In addition, we performed haplotype analysis of AtABCE2 and its paralogue AtABCE1 using genomic sequences of 1,135 A. thaliana ecotypes. Plant ABCE proteins showed overall high sequence conservation, sharing at least 78% of amino acid sequence identity with AtABCE2. We found that over half of the selected species have two to eight ABCE genes, suggesting that in plants ABCE genes can be classified as a low-copy gene family, rather than a single-copy gene family. The phylogenetic trees of ABCE protein sequences and the corresponding coding sequences demonstrated that Brassicaceae and Poaceae families have independently undergone lineage-specific split of the ancestral ABCE gene. Other plant species have gained ABCE gene copies through more recent duplication events. We also noticed that ploidy level but not ancient whole genome duplications experienced by a species impacts ABCE gene family size. Deeper analysis of AtABCE2 and AtABCE1 from 1,135 A. thaliana ecotypes revealed four and 35 non-synonymous SNPs, respectively. The lower natural variation in AtABCE2 compared to AtABCE1 is in consistence with its crucial role for plant viability. Overall, while the sequence of the ABCE protein family is highly conserved in the plant kingdom, many plants have evolved to have more than one copy of this essential translational factor.

Genome wide identification and expression profiling of ATP binding cassette (ABC) transporters gene family in lentil (Lens culinaris Medikus) under aluminium stress condition

Adenosine triphosphate-binding cassette transporters (ABC transporters) are involved in regulating plant growth, development and tolerance to environmental stresses. In this study, a total of 138 ABC transporter genes were identified in the lentil genome that were classified into eight subfamilies. Four lentil ABC transporters from subfamily B and I were clustered together with the previously characterized ABC transporter proteins related to aluminium (Al) detoxification. Lentil ABC transporter genes were distributed across the chromosomes. Tandem duplication was the main driving force for expansion of the ABC gene family. Collinearity of lentil with soybean indicated that ABC gene family is closely linked to Glycine max. ABC genes in the same subfamily showed similar gene structure and conserved motifs. The ABC promoter regions harboured a large number of plant hormones and multiple stress responsive cis-regulatory elements. The qRT-PCR showed that ABC genes had varied expression in roots of lentil at different time points under Al stress. This is the first report on genome wide identification and expression analyses of genes encoding ABC transporter genes in lentil which has provided in-depth insight for future research on evolution and elucidation of molecular mechanisms for aluminium tolerance.

The maize ATP-binding cassette (ABC) transporter ZmMRPA6 confers cold and salt stress tolerance in plants

KEY MESSAGE

ZmMRPA6 was cloned and characterized as the first ATP-binding cassette (ABC) transporter in maize to be proven to participate in cold and salt tolerance. Homologous genes AtABCC4 and AtABCC14 of ZmMRPA6 also responded to salt stress. ATP-binding cassette (ABC) proteins are major transmembrane transporters that play significant roles in plant development against various abiotic stresses. However, available information regarding stress-related ABC genes in maize is minimal. In this study, a maize ABC transporter gene, ZmMRPA6, was identified through genome-wide association analysis (GWAS) for cold tolerance in maize seeds germination and functionally characterized. During germination and seedling stages, the zmmrpa6 mutant exhibited enhanced resistance to cold or salt stress. Mutated of ZmMRPA6 did not affect the expression of downstream response genes related cold or salt response at the transcriptional level. Mass spectrometry analysis revealed that most of the differential proteins between zmmrpa6 and wild-type plants were involved in response to stress process including oxidative reduction, hydrolase activity, small molecule metabolism, and photosynthesis process. Meanwhile, the plants which lack the ZmMRPA6 homologous genes AtABCC4 or AtABCC14 were sensitive to salt stress in Arabidopsis. These results indicated that ZmMRPA6 and its homologous genes play a conserved role in cold and salt stress, and functional differentiation occurs in monocotyledonous and dicotyledonous plants. In summary, these findings dramatically improved our understanding of the function of ABC transporters resistance to abiotic stresses in plants.

Genome-Wide Identification and Expression Analysis of the Stearoyl-Acyl Carrier Protein Δ9 Desaturase Gene Family under Abiotic Stress in Barley

Stearoyl-acyl carrier protein (ACP) Δ9 desaturase (SAD) is a critical fatty acid dehydrogenase in plants, playing a prominent role in regulating the synthesis of unsaturated fatty acids (UFAs) and having a significant impact on plant growth and development. In this study, we conducted a comprehensive genomic analysis of the SAD family in barley (Hordeum vulgare L.), identifying 14 HvSADs with the FA_desaturase_2 domain, which were divided into four subgroups based on sequence composition and phylogenetic analysis, with members of the same subgroup possessing similar genes and motif structures. Gene replication analysis suggested that tandem and segmental duplication may be the major reasons for the expansion of the SAD family in barley. The promoters of HvSADs contained various cis-regulatory elements (CREs) related to light, abscisic acid (ABA), and methyl jasmonate (MeJA). In addition, expression analysis indicated that HvSADs exhibit multiple tissue expression patterns in barley as well as different response characteristics under three abiotic stresses: salt, drought, and cold. Briefly, this evolutionary and expression analysis of HvSADs provides insight into the biological functions of barley, supporting a comprehensive analysis of the regulatory mechanisms of oil biosynthesis and metabolism in plants under abiotic stress.

Genome-wide identification and characterization of ABC transporter superfamily in the legume Cajanus cajan

Plant ATP-binding cassette (ABC) protein family is the largest multifunctional highly conserved protein superfamily that transports diverse substrates across biological membranes by the hydrolysis of ATP and is also the part of the several other biological processes like cellular detoxification, growth and development, stress biology, and signaling processes. In the agriculturally important legume crop Cajanus cajan, a genome-wide identification and characterization of the ABC gene family was carried out. A total of 159 ABC genes were identified that belong to eight canonical classes CcABCA to CcABCG and CcABCI based on the phylogenetic analysis. The number of genes was highest in CcABCG followed by CcABCC and CcABCB class. A total of 85 CcABC genes were found on 11 chromosomes and 74 were found on scaffold. Tandem duplication was the major driver of CcABC gene family expansion. The dN/dS ratio revealed the purifying selection. The phylogenetic analysis revealed class-specific eight superclades which reflect their functional importance. The largest clade was found to be CcABCG which reflects their functional significance. CcABC proteins were mainly basic in nature and found to be localized in the plasma membrane. The secondary structure prediction revealed the dominance of α-helix. The canonical transmembrane and nucleotide binding domain, signature motif LSSGQ, Walker A, Walker B region, and Q loop were also identified. A class-specific exon-intron pattern was also observed. In addition to core elements, different cis-acting regulatory elements like stress, hormone, and cellular responsive were also identified. Expression profiling of CcABC genes at various developmental stages of different anatomical tissues was performed and it was noticed that CcABCF3, CcABCF4, CcABCF5, CcABCG66, and CcABCI3 had the highest expression. The results of the current study endow us with the further functional analysis of Cajanus ABC in the future.

Genome-Wide Identification and Analysis of the ABCF Gene Family in Triticum aestivum

The ATP-binding cassette (ABC) superfamily of proteins is a group of evolutionarily conserved proteins. The ABCF subfamily is involved in ribosomal synthesis, antibiotic resistance, and transcriptional regulation. However, few studies have investigated the role of ABCF in wheat (Triticum aestivum) immunity. Here, we identified 18 TaABCFs and classified them into four categories based on their domain characteristics. Functional similarity between Arabidopsis and wheat ABCF genes was predicted using phylogenetic analysis. A comprehensive genome-wide analysis of gene structure, protein motifs, chromosomal location, and cis-acting elements was also performed. Tissue-specific analysis and expression profiling under temperature, hormonal, and viral stresses were performed using real-time quantitative reverse transcription polymerase chain reaction after randomly selecting one gene from each group. The results revealed that all TaABCF genes had the highest expression at 25 °C and responded to methyl jasmonate induction. Notably, TaABCF2 was highly expressed in all tissues except the roots, and silencing it significantly increased the accumulation of Chinese wheat mosaic virus or wheat yellow mosaic virus in wheat leaves. These results indicated that TaABCF may function in response to viral infection, laying the foundation for further studies on the mechanisms of this protein family in plant defence.

Genome-wide identification and expression pattern profiling of the ATP-binding cassette gene family in tea plant (Camelliasinensis)

The ATP-binding cassette (ABC) gene family is one of the largest and oldest protein families, consisting of ATP-driven transporters facilitating substrate transportation across cell membranes. However, little is known about the evolution and biological function of the ABC gene family in tea plants. In this study, we performed a genome-wide identification and expression analysis of genes encoding ABC transporter proteins in Camellia sinensis. Our analysis of 170 ABC genes revealed that CsABCs were unevenly distributed across 15 chromosomes, with an amino acid length ranging from 188 to 2489 aa, molecular weight ranging from 20.29 to 277.34 kDa, and an isoelectric point ranging from 4.89 to 10.63. Phylogenetic analysis showed that CsABCs were divided into eight subfamilies, among which the ABCG subfamily was the most abundant. Furthermore, the subcellular localization of CsABCs indicated that they were present in various organelles. Collinearity analysis between the tea plant and Arabidopsis thaliana genomes revealed that the CsABC genes were homologous to the AtABC genes. Large gene fragment duplication analysis identified ten gene pairs as tandem repeats, and interaction network analysis demonstrated that CsABCs interacted with various types of target genes, with protein interactions also occurring within the family. Tissue expression analysis indicated that CsABCs were highly expressed in roots, stems, and leaves and were easily induced by drought and cold stress. Moreover, qRT-PCR analysis of the relative expression level of the gene under drought and cold stress correlated with the sequencing results. Identifying ABC genes in tea plants lays a foundation for the classification and functional analysis of ABC family genes, which can facilitate molecular breeding and the development of new tea varieties.

Impact of Some Toxic Metals on Important ABC Transporters in Soybean (Glycine max L.)

In plants, ATP-binding cassette (ABC) transporters facilitate the movement of substrates across membranes using ATP for growth, development, and defense. Soils contaminated with toxic metals such as cadmium (Cd) and mercury (Hg) might adversely affect the metabolism of plants and humans. In this study, a phylogenetic relationship among soybeans' (Glycine max) ATP binding cassette (GmABCs) and other plant ABCs was analyzed using sequence information, gene structure, chromosomal distribution, and conserved motif-domain. The ontology of GmABCs indicated their active involvement in trans-membrane transport and ATPase activity. Thirty-day-old soybean plants were exposed to 100 μM CdCl2 and 100 μM HgCl2 for 10 days. Physiological and biochemical traits were altered under stress conditions. Compared to Control, GmABC transporter genes were differentially expressed in response to Cd and Hg. The qRT-PCR data showed upregulation of seven ABC transporter genes in response to Cd stress and three were downregulated. On the other hand, Hg stress upregulated four GmABC genes and downregulated six. It could be concluded that most of the ABCB and ABCG subfamily members were actively involved in heavy metal responses. Real-time expression studies suggest the function of specific ABC transporters in Cd and Hg stress response and are helpful in future research to develop stress-tolerant varieties of soybean.

Over-expression of the barley Phytoglobin 1 (HvPgb1) evokes leaf-specific transcriptional responses during root waterlogging

Oxygen deprivation (hypoxia) in the root due to waterlogging causes profound metabolic changes in the aerial organs depressing growth and limiting plant productivity in barley (Hordeum vulgare L.). Genome-wide analyses in waterlogged wild type (WT) barley (cv. Golden Promise) plants and plants over-expressing the phytoglobin 1 HvPgb1 [HvPgb1(OE)] were performed to determine leaf specific transcriptional responses during waterlogging. Normoxic WT plants outperformed their HvPgb1(OE) counterparts for dry weight biomass, chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration. Root waterlogging severely depressed all these parameters in WT plants but not in HvPgb1(OE) plants, which exhibited an increase in photosynthetic rate. In leaftissue, root waterlogging repressed genes encoding photosynthetic components and chlorophyll biosynthetic enzymes, while induced those of reactive oxygen species (ROS)-generating enzymes. This repression was alleviated in HvPgb1(OE) leaves which also exhibited an induction of enzymes participating in antioxidant responses. In the same leaves, the transcript levels of several genes participating in nitrogen metabolism were also higher relative to WT leaves. Ethylene levels were diminished by root waterlogging in leaves of WT plants, but not in HvPgb1(OE), which were enriched in transcripts of ethylene biosynthetic enzymes and ethylene response factors. Pharmacological treatments increasing the level or action of ethylene further suggested the requirement of ethylene in plant response to root waterlogging. In natural germplasm an elevation in foliar HvPgb1 between 16h and 24h of waterlogging occurred in tolerant genotypes but not in susceptible ones. By integrating morpho-physiological parameters with transcriptome data, this study provides a framework defining leaf responses to root waterlogging and indicates that the induction of HvPgb1 may be used as a selection tool to enhance resilience to excess moisture.

Transcriptome profiling disclosed the effect of single and combined drought and heat stress on reprogramming of genes expression in barley flag leaf

Despite numerous studies aimed at unraveling the genetic background of barley's response to abiotic stress, the modulation of the transcriptome induced by combinatorial drought and increased temperature remains largely unrecognized. Very limited studies were done, especially on the flag leaf, which plays an important role in grain filling in cereals. In the present study, transcriptome profiles, along with chlorophyll fluorescence parameters and yield components, were compared between barley genotypes with different flag leaf sizes under single and combined drought and heat stress. High-throughput mRNA sequencing revealed 2,457 differentially expressed genes, which were functionally interpreted using Gene Ontology term enrichment analysis. The transcriptomic signature under double stress was more similar to effects caused by drought than by elevated temperature; it was also manifested at phenotypic and chlorophyll fluorescence levels. Both common and stress-specific changes in transcript abundance were identified. Genes regulated commonly across stress treatments, determining universal stress responses, were associated, among others, with responses to drought, heat, and oxidative stress. In addition, changes specific to the size of the flag leaf blade were found. Our study allowed us to identify sets of genes assigned to various processes underlying the response to drought and heat, including photosynthesis, the abscisic acid pathway, and lipid transport. Genes encoding LEA proteins, including dehydrins and heat shock proteins, were especially induced by stress treatments. Some association between genetic composition and flag leaf size was confirmed. However, there was no general coincidence between SNP polymorphism of genotypes and differential expression of genes induced by stress factors. This research provided novel insight into the molecular mechanisms of barley flag leaf that determine drought and heat response, as well as their co-occurrence.

Reprisal of Schima superba to Mn stress and exploration of its defense mechanism through transcriptomic analysis

One of the most diverse protein families, ATP-binding cassette (ABC) transporters, play a role in disease resistance, heavy metal tolerance, and food absorption.Differentially expressed genes contribute in the investigation of plant defense mechanisms under varying stress conditions. To elucidate the molecular mechanisms involved in Mn metal stress, we performed a transcriptomic analysis to explore the differential gene expression in Schima superba with the comparison of control. A total of 79.84 G clean data was generated and 6558 DEGs were identified in response to Mn metal stress. Differentially expressed genes were found to be involved in defense, signaling pathways, oxidative burst, transcription factors and stress responses. Genes important in metal transport were more expressive in Mn stress than control plants. The investigation of cis-acting regions in the ABC family indicated that these genes might be targeted by a large variety of trans-acting elements to control a variety of stress circumstances. Moreover, genes involved in defense responses, the mitogen-activated protein kinase (MAPK) signaling and signal transduction in S. superba were highly induced in Mn stress. Twenty ABC transporters were variably expressed on 1st, 5th, and 10th day of Mn treatment, according to the qRT PCR data. Inclusively, our findings provide an indispensable foundation for an advanced understanding of the metal resistance mechanisms. Our study will enrich the sequence information of S. superba in a public database and would provide a new understanding of the molecular mechanisms of heavy metal tolerance and detoxification.

Combined transcriptomic and metabolomic analysis reveals a role for adenosine triphosphate-binding cassette transporters and cell wall remodeling in response to salt stress in strawberry

Strawberry (Fragaria × ananassa Duch) are sensitive to salt stress, and breeding salt-tolerant strawberry cultivars is the primary method to develop resistance to increased soil salinization. However, the underlying molecular mechanisms mediating the response of strawberry to salinity stress remain largely unknown. This study evaluated the salinity tolerance of 24 strawberry varieties, and transcriptomic and metabolomic analysis were performed of 'Sweet Charlie' (salt-tolerant) and 'Benihoppe' (salt-sensitive) to explore salt tolerance mechanisms in strawberry. Compared with the control, we identified 3412 differentially expressed genes (DEGs) and 209 differentially accumulated metabolites (DAMs) in 'Benihoppe,' and 5102 DEGs and 230 DAMs in 'Sweet Charlie.' DEGs Gene Ontology (GO) enrichment analyses indicated that the DEGs in 'Benihoppe' were enriched for ion homeostasis related terms, while in 'Sweet Charlie,' terms related to cell wall remodeling were over-represented. DEGs related to ion homeostasis and cell wall remodeling exhibited differential expression patterns in 'Benihoppe' and 'Sweet Charlie.' In 'Benihoppe,' 21 ion homeostasis-related DEGs and 32 cell wall remodeling-related DEGs were upregulated, while 23 ion homeostasis-related DEGs and 138 cell wall remodeling-related DEGs were downregulated. In 'Sweet Charlie,' 72 ion homeostasis-related DEGs and 275 cell wall remodeling-related DEGs were upregulated, while 11 ion homeostasis-related DEGs and 20 cell wall remodeling-related DEGs were downregulated. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed only four KEGG enriched pathways were shared between 'Benihoppe' and 'Sweet Charlie,' including flavonoid biosynthesis, phenylalanine metabolism, phenylpropanoid biosynthesis and ubiquinone, and other terpenoid-quinone biosynthesis. Integrating the results of transcriptomic and metabolomics analyses showed that adenosine triphosphate-binding cassette (ABC) transporters and flavonoid pathway genes might play important roles in the salt stress response in strawberry, and DAMs and DEGs related to ABC transporter and flavonoid pathways were differentially expressed or accumulated. The results of this study reveal that cell wall remodeling and ABC transporters contribute to the response to salt stress in strawberry, and that related genes showed differential expression patterns in varieties with different salt tolerances. These findings provide new insights into the underlying molecular mechanism of strawberry response to salt stress and suggest potential targets for the breeding of salt-tolerant strawberry varieties.

Genome-Wide Analysis of the ATP-Binding Cassette (ABC) Transporter Family in Zea mays L. and Its Response to Heavy Metal Stresses

The ATP-binding cassette (ABC) transporter family is one of the largest eukaryotic protein families. Its members play roles in numerous metabolic processes in plants by releasing energy for substrate transport across membranes through hydrolysis of ATP. Maize belongs to the monocotyledonous plant family, Gramineae, and is one of the most important food crops in the world. We constructed a phylogenetic tree with individual ABC genes from maize, rice, sorghum, Arabidopsis, and poplar. This revealed eight families, each containing ABC genes from both monocotyledonous and dicotyledonous plants, indicating that the amplification events of ABC gene families predate the divergence of plant monocotyledons. To further understand the functions of ABC genes in maize growth and development, we analyzed the expression patterns of maize ABC family genes in eight tissues and organs based on the transcriptome database on the Genevestigator website. We identified 133 ABC genes expressed in most of the eight tissues and organs examined, especially during root and leaf development. Furthermore, transcriptome analysis of ZmABC genes showed that exposure to metallic lead induced differential expression of many maize ABC genes, mainly including ZmABC 012, 013, 015, 031, 040, 043, 065, 078, 080, 085, 088, 102, 107, 111, 130 and 131 genes, etc. These results indicated that ZmABC genes play an important role in the response to heavy metal stress. The comprehensive analysis of this study provides a foundation for further studies into the roles of ABC genes in maize.

Transcriptome-wide m6A methylation profile reveals regulatory networks in roots of barley under cadmium stress

Cadmium (Cd) pollutants restrict crop yield and food security in long-term agricultural activities. Crops have evolved adaptive strategies under Cd condition, however, the transcriptional regulatory mechanism of Cd-tolerant genes remains to be largely illustrated. In this study, barley roots were exposed to 5 µM CdCl₂ for physiological response and transcriptome-wide m6A methylation profile. Cd stress inhibited root growth after 7 d Cd treatment, which is mainly associated with inhibited absorption of Mn. After Cd treatment, 8151 significantly modified m6A sites and 3920 differentially expressed genes were identified. Transcriptome-wide m6A hypermethylation was widely induced by Cd stress and enriched near the stop codon and 3' UTR regions. Among 435 m6A modified DEGs, 319 hypermethylated genes were up-regulated and 84 hypomethylated genes were down-regulated, respectively, indicating a positive correlation of m6A methylation and expression. But well-known Cd transporter genes (HvNramp5, HvIRT1, HvHMA3, etc.) were not modified by m6A methylation, except for ABC transporters. We further found key Cd-responding regulatory genes were positively modulated with m6A methylation, including MAPK, WRKY and MYB members. This study proposed a transcriptional regulatory network of Cd stress response in barley roots, which may provide new insight into gene manipulation of controlling low Cd accumulation for crops.

ATP-binding cassette transporters in nonmodel plants

Knowledge about plant ATP-binding cassette (ABC) proteins is of great value for sustainable agriculture, economic yield, and the generation of high-quality products, especially under unfavorable growth conditions. We have learned much about ABC proteins in model organisms, notably Arabidopsis thaliana; however, the importance of research dedicated to these transporters extends far beyond Arabidopsis biology. Recent progress in genomic and transcriptomic approaches for nonmodel and noncanonical model plants allows us to look at ABC transporters from a wider perspective and consider chemodiversity and functionally driven adaptation as distinctive mechanisms during their evolution. Here, by considering several representatives from agriculturally important families and recent progress in functional characterization of nonArabidopsis ABC proteins, we aim to bring attention to understanding the evolutionary background, distribution among lineages and possible mechanisms underlying the adaptation of this versatile transport system for plant needs. Increasing the knowledge of ABC proteins in nonmodel plants will facilitate breeding and development of new varieties based on, for example, genetic variations of endogenous genes and/or genome editing, representing an alternative to transgenic approaches.

Auxin Transporters-A Biochemical View

From embryogenesis to fruit formation, almost every aspect of plant development and differentiation is controlled by the cellular accumulation or depletion of auxin from cells and tissues. The respective auxin maxima and minima are generated by cell-to-cell auxin transport via transporter proteins. Differential auxin accumulation as a result of such transport processes dynamically regulates auxin distribution during differentiation. In this review, we introduce all auxin transporter (families) identified to date and discuss the knowledge on prominent family members, namely, the PIN-FORMED exporters, ATP-binding cassette B (ABCB)-type transporters, and AUX1/LAX importers. We then concentrate on the biochemical features of these transporters and their regulation by posttranslational modifications and interactors.

Involvement of several putative transporters of different families in β-cyclocitral-induced alleviation of cadmium toxicity in quinoa (Chenopodium quinoa) seedlings

Cadmium (Cd) has a serious negative impact on crop growth and human food security. This study investigated the alleviating effect of β-cyclocitral, a potential heavy metal barrier, on Cd stress in quinoa seedlings and the associated mechanisms. Our results showed that β-cyclocitral alleviated Cd stress-induced growth inhibition in quinoa seedlings and promoted quinoa seedling root development under Cd stress. Moreover, it maintained the antioxidant system of quinoa seedlings, including the enzymatic, i.e., superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and nonenzymatic, i.e., reduced glutathione (GSH) and ascorbic acid (ASA), antioxidants, which eliminate the damage from excessive reactive oxygen species (ROS). Our results showed that β-cyclocitral could reduce the amount of Cd absorbed by roots. Furthermore, we systematically identified five transporter families from the quinoa genome, and the RT-qPCR results showed that ZIP, Nramp and YSL gene families were downregulated by β-cyclocitral to reduce Cd uptake by roots. Thus, β-cyclocitral promoted the growth, photosynthetic capacity and antioxidant capacity of the aboveground parts of quinoa seedlings. Taken together, these results suggested that the β-cyclocitral-induced decrease in Cd uptake may be caused by the downregulation of several selected transporter genes.

Genome-Wide Identification of the HMA Gene Family and Expression Analysis under Cd Stress in Barley

In recent years, cadmium (Cd) pollution in soil has increased with increasing industrial activities, which has restricted crop growth and agricultural development. The heavy metal ATPase (HMA) gene family contributes to heavy metal stress resistance in plants. In this study, 21 HMA genes (HvHMAs) were identified in barley (Hordeumvulgare L., Hv) using bioinformatics methods. Based on phylogenetic analysis and domain distribution, barley HMA genes were divided into five groups (A-E), and complete analyses were performed in terms of physicochemical properties, structural characteristics, conserved domains, and chromosome localization. The expression pattern analysis showed that most HvHMA genes were expressed in barley and exhibited tissue specificity. According to the fragments per kilobase of exon per million fragments values in shoots from seedlings at the 10 cm shoot stage (LEA) and phylogenetic analysis, five HvHMA genes were selected for expression analysis under Cd stress. Among the five HvHMA genes, three (HvHMA1, HvHMA3, and HvHMA4) were upregulated and two (HvHMA2 and HvHMA6) were downregulated following Cd treatments. This study serves as a foundation for clarifying the functions of HvHMA proteins in the heavy metal stress resistance of barley.