Progress in genetic engineering of peanut (Arachis hypogaea L.)--a review

Transcriptional alterations of peanut root during interaction with growth-promoting Tsukamurella tyrosinosolvens strain P9

The plant growth-promoting rhizobacterium Tsukamurella tyrosinosolvens P9 can improve peanut growth. In this study, a co-culture system of strain P9 and peanut was established to analyze the transcriptome of peanut roots interacting with P9 for 24 and 72 h. During the early stage of co-culturing, genes related to mitogen-activated protein kinase (MAPK) and Ca2+ signal transduction, ethylene synthesis, and cell wall pectin degradation were induced, and the up-regulation of phenylpropanoid derivative, flavonoid, and isoflavone synthesis enhanced the defense response of peanut. The enhanced expression of genes associated with photosynthesis and carbon fixation, circadian rhythm regulation, indoleacetic acid (IAA) synthesis, and cytokinin decomposition promoted root growth and development. At the late stage of co-culturing, ethylene synthesis was reduced, whereas Ca2+ signal transduction, isoquinoline alkaloid synthesis, and ascorbate and aldarate metabolism were up-regulated, thereby maintaining root ROS homeostasis. Sugar decomposition and oxidative phosphorylation and nitrogen and fatty acid metabolism were induced, and peanut growth was significantly promoted. Finally, the gene expression of seedlings inoculated with strain P9 exhibited temporal differences. The results of our study, which explored transcriptional alterations of peanut root during interacting with P9, provide a basis for elucidating the growth-promoting mechanism of this bacterial strain in peanut.

Genome-wide identification of TPS and TPP genes in cultivated peanut (Arachis hypogaea) and functional characterization of AhTPS9 in response to cold stress

Introduction

Trehalose is vital for plant metabolism, growth, and stress resilience, relying on Trehalose-6-phosphate synthase (TPS) and Trehalose-6-phosphate phosphatase (TPP) genes. Research on these genes in cultivated peanuts (Arachis hypogaea) is limited.

Methods

This study employed bioinformatics to identify and analyze AhTPS and AhTPP genes in cultivated peanuts, with subsequent experimental validation of AhTPS9's role in cold tolerance.

Results

In the cultivated peanut genome, a total of 16 AhTPS and 17 AhTPP genes were identified. AhTPS and AhTPP genes were observed in phylogenetic analysis, closely related to wild diploid peanuts, respectively. The evolutionary patterns of AhTPS and AhTPP genes were predominantly characterized by gene segmental duplication events and robust purifying selection. A variety of hormone-responsive and stress-related cis-elements were unveiled in our analysis of cis-regulatory elements. Distinct expression patterns of AhTPS and AhTPP genes across different peanut tissues, developmental stages, and treatments were revealed, suggesting potential roles in growth, development, and stress responses. Under low-temperature stress, qPCR results showcased upregulation in AhTPS genes (AhTPS2-5, AhTPS9-12, AhTPS14, AhTPS15) and AhTPP genes (AhTPP1, AhTPP6, AhTPP11, AhTPP13). Furthermore, AhTPS9, exhibiting the most significant expression difference under cold stress, was obviously induced by cold stress in cultivated peanut, and AhTPS9-overexpression improved the cold tolerance of Arabidopsis by protect the photosynthetic system of plants, and regulates sugar-related metabolites and genes.

Discussion

This comprehensive study lays the groundwork for understanding the roles of AhTPS and AhTPP gene families in trehalose regulation within cultivated peanuts and provides valuable insights into the mechanisms related to cold stress tolerance.

Advances in omics research on peanut response to biotic stresses

Peanut growth, development, and eventual production are constrained by biotic and abiotic stresses resulting in serious economic losses. To understand the response and tolerance mechanism of peanut to biotic and abiotic stresses, high-throughput Omics approaches have been applied in peanut research. Integrated Omics approaches are essential for elucidating the temporal and spatial changes that occur in peanut facing different stresses. The integration of functional genomics with other Omics highlights the relationships between peanut genomes and phenotypes under specific stress conditions. In this review, we focus on research on peanut biotic stresses. Here we review the primary types of biotic stresses that threaten sustainable peanut production, the multi-Omics technologies for peanut research and breeding, and the recent advances in various peanut Omics under biotic stresses, including genomics, transcriptomics, proteomics, metabolomics, miRNAomics, epigenomics and phenomics, for identification of biotic stress-related genes, proteins, metabolites and their networks as well as the development of potential traits. We also discuss the challenges, opportunities, and future directions for peanut Omics under biotic stresses, aiming sustainable food production. The Omics knowledge is instrumental for improving peanut tolerance to cope with various biotic stresses and for meeting the food demands of the exponentially growing global population.

Red fluorescence protein (DsRed2) promotes the screening efficiency in peanut genetic transformation

Peanut (Arachis hypogaea L.), one of the leading oilseed crops worldwide, is an important source of vegetable oil, protein, minerals and vitamins. Peanut is widely cultivated in Asia, Africa and America, and China is the largest producer and consumer of peanut. Genetic engineering has shown great potential to alter the DNA makeup of an organism which is largely hindered by the low transformation and screening efficiency including in peanut. DsRed2 is a reporter gene widely utilized in genetic transformation to facilitate the screening of transformants, but never used in peanut genetic transformation. In this study, we have demonstrated the potential of the red fluorescence protein DsRed2 as a visual reporter to improve screening efficiency in peanut. DsRed2 was firstly expressed in protoplasts isolated from peanut cultivar Zhonhua 12 by PEG, and red fluorescence was successfully detected. Then, DsRed2 was expressed in peanut plants Zhonghua 12 driven by 35S promoter via Agrobacterium tumefaciens-mediated transformation. Red fluorescence was visually observed in calli and regenerated shoots, as well as in roots, leaves, flowers, fresh pod shells and mature seeds, suggesting that transgenic screening could be initiated at the early stage of transformation, and continued to the progeny. Upon screening with DsRed2, the positive plant rate was increased from 56.9% to 100%. The transgenic line was then used as the male parent to be crossed with Zhonghua 24, and the hybrid seeds showed red fluorescence as well, indicating that DsRed2 could be applied to hybrid plant identification very efficiently. DsRed2 was also expressed in hairy roots of Huayu 23 via Agrobacterium rhizogenes-mediated transformation, and the transgenic roots were easily selected by red fluorescence. In summary, the DsRed2 is an ideal reporter to achieve maximum screening efficiency and accuracy in peanut genetic transformation.

Genome-wide characterization of phospholipase D family genes in allotetraploid peanut and its diploid progenitors revealed their crucial roles in growth and abiotic stress responses

Abiotic stresses such as cold, drought and salinity are the key environmental factors that limit the yield and quality of oil crop peanut. Phospholipase Ds (PLDs) are crucial hydrolyzing enzymes involved in lipid mediated signaling and have valuable functions in plant growth, development and stress tolerance. Here, 22, 22 and 46 PLD genes were identified in Arachis duranensis, Arachis ipaensis and Arachis hypogaea, respectively, and divided into α, β, γ, δ, ε, ζ and φ isoforms. Phylogenetic relationships, structural domains and molecular evolution proved the conservation of PLDs between allotetraploid peanut and its diploid progenitors. Almost each A. hypogaea PLD except for AhPLDα6B had a corresponding homolog in A. duranensis and A. ipaensis genomes. The expansion of Arachis PLD gene families were mainly attributed to segmental and tandem duplications under strong purifying selection. Functionally, the most proteins interacting with AhPLDs were crucial components of lipid metabolic pathways, in which ahy-miR3510, ahy-miR3513-3p and ahy-miR3516 might be hub regulators. Furthermore, plenty of cis-regulatory elements involved in plant growth and development, hormones and stress responses were identified. The tissue-specific transcription profiling revealed the broad and unique expression patterns of AhPLDs in various developmental stages. The qRT-PCR analysis indicated that most AhPLDs could be induced by specific or multiple abiotic stresses. Especially, AhPLDα3A, AhPLDα5A, AhPLDβ1A, AhPLDβ2A and AhPLDδ4A were highly up-regulated under all three abiotic stresses, whereas AhPLDα9A was neither expressed in 22 peanut tissues nor induced by any abiotic stresses. This genome-wide study provides a systematic analysis of the Arachis PLD gene families and valuable information for further functional study of candidate AhPLDs in peanut growth and abiotic stress responses.

Identification of Peanut AhMYB44 Transcription Factors and Their Multiple Roles in Drought Stress Responses

MYB transcription factors (TFs) comprise a large gene family that plays an important role in plant growth, development, stress responses, and defense regulation. However, their functions in peanut remain to be further elucidated. Here, we identified six AhMYB44 genes (AhMYB44-01/11, AhMYB44-05/15, and AhMYB44-06/16) in cultivated peanut. They are typical R2R3-MYB TFs and have many similarities but different expression patterns in response to drought stress, suggesting different functions under drought stress. Homologous genes with higher expression in each pair were selected for further study. All of them were nuclear proteins and had no self-transactivation activity. In addition, we compared the performances of different lines at germination, seedling, and adult stages under drought stress. After drought treatment, the overexpression of AhMYB44-11 transgenic plants resulted in the longest root length at the seedling stage. Levels of proline, soluble sugar and chlorophyll, and expression levels of stress-related genes, including P5CS1, RD29A, CBF1, and COR15A, were higher than those of the wild type (WT) at the adult stage. While the overexpression of AhMYB44-16 significantly increased the drought sensitivity of plants at all stages, with differential ABA content, the expression levels of the ABA-related genes PP2CA and ABI1 were significantly upregulated and those of ABA1 and ABA2 were significantly downregulated compared with the WT. AhMYB44-05 showed similar downregulated expression as AhMYB44-16 under drought stress, but its overexpression in Arabidopsis did not significantly affect the drought resistance of transgenic plants. Based on the results, we propose that AhMYB44-11 plays a role as a positive factor in drought tolerance by increasing the transcription abundance of stress-related genes and the accumulation of osmolytes, while AhMYB44-16 negatively regulates drought tolerance through its involvement in ABA-dependent stress response pathways.

Genome wide identification and characterization of nodulation related genes in Arachis hypogaea

Nitrogen is an important plant nutrient that has a significant role in crop yield. Hence, to fulfill the needs of sustainable agriculture, it is necessary to improve biological nitrogen fixation in leguminous crops. Nod inducing gene families plays a crucial role in the interaction between rhizobia and legumes, leading to biological nitrogen fixation. However, nod inducing genes identification and characterization has not yet been performed in Arachis hypogaea. In this study, identification and genome-wide analysis of nod inducing genes are performed so that to explore their potential functions in the Arachis hypogaea for the first time. Nod genes were comprehensively analyzed by phylogenetic clustering analysis, gene structure determination, detection of conserved motifs, subcellular localization, conserved motifs, cis-acting elements and promoter region analysis. This study identified 42 Nod inducing genes in Arachis hypogaea, their sequences were submitted to NCBI and accession numbers were obtained. Potential involvement of these genes in biological nitrogen fixation has been unraveled, such as, phylogenetic analysis revealed that nod inducing genes evolved independently in Arachis hypogaea, the amino acid structures exhibited 20 highly conserved motifs, the proteins are present at different locations in cells and the gene structures revealed that all the genes are full-length genes with upstream intronic regions. Further, the promoter analysis determined a large number of cis-regulatory elements involved in nodulation. Moreover, this study not only provides identification and characterization of genes underlying developmental and functional stages of nodulation and biological nitrogen fixation but also lays the foundation for further revelation of nod inducing gene family. Besides, identification and structural analysis of these genes in Arachis hypogaea may provide a theoretical basis for the study of evolutionary relationships in future analysis.

Chicoric Acid: Natural Occurrence, Chemical Synthesis, Biosynthesis, and Their Bioactive Effects

Chicoric acid has been widely used in food, medicine, animal husbandry, and other commercial products because of its significant pharmacological activities. However, the shortage of chicoric acid limits its further development and utilization. Currently, Echinacea purpurea (L.) Moench serves as the primary natural resource of chicoric acid, while other sources of it are poorly known. Extracting chicoric acid from plants is the most common approach. Meanwhile, chicoric acid levels vary in different plants as well as in the same plant from different areas and different medicinal parts, and different extraction methods. We comprehensively reviewed the information regarding the sources of chicoric acid from plant extracts, its chemical synthesis, biosynthesis, and bioactive effects.

An Improvised Hairy Root Transformation Method for Efficient Gene Silencing in Roots and Nodules of Arachis hypogaea

Peanut (Arachis hypogaea) is a major oilseed crop and is widely cultivated in tropical and subtropical climate zone worldwide. Peanut belongs to the Papilionoid family with an atypical nodule developmental program. In particular, rhizobia enter through developmental cracks and lead to the formation of aeschynomenoid subtype determinate nodules. Peanut nodules are efficient nitrogen-fixers and form swollen bacteroid containing symbiosomes. The allotetraploid genome and recalcitrance to stable transformation used to be the major bottleneck for peanut biologists. Recent genome sequencing of peanut cultivar Tifrunner has opened up a huge opportunity for molecular research. A composite plant contains transformed roots with a non-transformed shoot. The composite plant-based approach has already proven to be a tool of choice for high throughput studies in root biology. The available protocols failed to generate efficient hairy root transformation in the genome sequenced cultivar Tifrunner. Here we describe an efficient hairy root transformation and composite plant generation protocol for the peanut cultivar Tifrunner. Our protocol generated ~92% plant regeneration efficiency with between 21.8% and 58.6% co-transformed root regeneration. We also show that this protocol can be efficiently used for protein localization, promoter GUS analysis, monitoring hormone response, and RNAi mediated knockdown of the genes using genome sequenced cultivar Tifrunner.

LncRNA-mediated ceRNA networks provide novel potential biomarkers for peanut drought tolerance

Drought stress has been the major constraint on peanut yield and quality, and an understanding of the function of long non-coding (lncRNAs) in the peanut drought stress response is still in its infancy. In this study, two peanut varieties with contrasting drought tolerance were used to explore the functions of lncRNAs in the peanut drought response, and the results showed that the drought-tolerant variety presented greater antioxidant enzyme activity, osmotic adjustment ability, and photosynthesis under drought conditions. There were 4329 lncRNAs identified in the two varieties, of which 535 and 663 lncRNAs were differentially expressed in NH5 and FH18, respectively. The cis targets of the differentially expressed lncRNAs were putatively involved in secondary metabolite biosynthesis and other basic metabolic processes. A total of 673 competing endogenous RNA (ceRNA) pairs were selected specifically in NH5, and the associated ceRNA network revealed six lncRNAs, MSTRG.70535.2, MSTRG.86570.2, MSTRG.86570.1, MSTRG.100618.1, MSTRG.81214.2, and MSTRG.30931.1were considered as hub nodes. They were speculated to contribute to enhancing peanut drought tolerance, such as regulating transcription and plant growth processes, thereby improving the drought stress response. In this study, lncRNAs and mRNAs interaction networks were constructed to aid a comprehensive understanding of the peanut drought stress response and form a basis for future research.

Immune response gene coexpression network analysis of Arachis hypogaea infected with Aspergillus flavus

Aspergillus flavus (A. flavus) infection and aflatoxin contamination is a major bottleneck for peanut cultivation and value chain industry. In this study, a transcriptomic network study was conducted by retrieving publically available RNA-seq datasets of resistant and susceptible peanut varieties infected by A. flavus separately to understand the peanut defense mechanism against A. flavus. The gene expression analysis revealed differentially expressed genes (DEGs) in response to the different levels of infection and coexpression network of DEGs deciphered hub genes involved in the immune process in resistant and susceptible varieties. The interplay of resistance conferring genes and cell wall related genes was observed through functional enrichment analysis in response to pathogen infection and identified few key genes such as Protein P21, R genes, Pattern Recognition Receptor genes, Pectinesterases, Laccase and Thaumatin-like protein 1b as candidate genes in imparting immune response against A. flavus.

Enterobacter hormaechei (MF957335) enhanced yield, disease and salinity tolerance in tomato

Soil salinity is one of the major limiting factors for poor crop yield in the world. Increasing salinity in the soil is a challenge for agriculture. In the recent past, plant growth-promoting rhizobacteria (PGPR) are being used to enhance plant growth in various conditions. However, the saline-tolerant PGPR are of great use for plant growth under saline condition. In the present study, saline-tolerant E. hormaechei (MF957335) was isolated from saline water. E. hormaechei (MF957335) was tested for its potassium and calcium solubilizing efficiency using Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX). E. hormaechei (MF957335) and K-Feldspar treatments significantly increased plant growth as compared to untreated plants (negative control). E. hormaechei (MF957335) significantly increased fresh biomass, shoot and root length of tomato plants. Among all the NaCl treatments, maximum fruits (9.66) were achieved in 250 mM NaCl + E. hormaechei treatment. Similar results with increased fruit numbers were obtained in K-Feldspar-treated plants. Apart from the plant growth, fresh biomass and fruit numbers, tomatoes from K-Feldspar-treated plants were large, fleshy and deep red colored. The study could demonstrate bioavailability of potassium from K-feldspar for tomato cultivation. Control plants tomato were small, non-fleshy, yellowish red, and infected with calcium deficiency disease blossom-end rot. The present study demonstrates the role of E. hormaechei (MF957335) in plant growth, yield promotion and disease tolerance by potassium and calcium solubilization, respectively. The study showed that E. hormaechei (MF957335) could be applied to saline and non-saline soils to enhance tomato yield.

Dual Microbial Inoculation, a Game Changer? - Bacterial Biostimulants With Multifunctional Growth Promoting Traits to Mitigate Salinity Stress in Spring Mungbean

Soil microbes play a vital role in improving plant growth, soil health, ameliorate biotic/abiotic stress and enhance crop productivity. The present study was aimed to investigate a coordinated effect of compatible consortium [salt tolerating Rhizobium and rhizobacterium with 1-aminocyclopropane-1-carboxylate (ACC) deaminase] in enhancing plant growth promoting (PGP) traits, symbiotic efficiency, nutrient acquisition, anti-oxidative enzymes, grain yield and associated profitability in spring mungbean. We identified a non-pathogenic compatible Rhizobium sp. LSMR-32 (MH644039.1) and Enterococcus mundtii LSMRS-3 (MH644178.1) from salt affected areas of Punjab, India and the same were assessed to develop consortium biofertilizer based on salt tolerance, multifarious PGP traits, antagonistic defense activities and presence of nifH, acds, pqq, and ipdc genes. Indole Acetic acid (IAA), P-solubilization, biofilm formation, exo-polysaccharides, siderophore, salt tolerance, ACC deaminase activities were all found highly significant in dual inoculant (LSMR-32 + LSMRS-3) treatment compared to LSMR-32 alone. Under saline soil conditions, dual inoculant showed a higher seed germination, plant height, biomass, chlorophyll content and macro and micro-nutrient uptake, than un-inoculated control. However, symbiotic (nodulation, nodule biomass and leghaemoglobin content) and soil quality parameters (phosphatase and soil dehydrogenase enzymes) increased numerically with LSMR-32 + LSMRS-3 over Rhizobium sp. LSMR-32 alone. Dual bacterial inoculation (LSMR-32 + LSMRS-3) increased the proline content (2.05 fold), anti-oxidative enzymes viz., superoxide dismutase (1.50 fold), catalase (1.43 fold) and peroxidase (3.88 folds) in contrast to control treatment. Decreased Na⁺ accumulation and increased K⁺ uptake resulted in favorable K⁺/Na⁺ ratio through ion homeostasis. Co-inoculation of Rhizobium sp. LSMR-32 and Enterococcus mundtii LSMRS-3 significantly improved the grain yield by 8.92% and led to superior B: C ratio over Rhizobium sp. alone under salt stress. To best of our knowledge this is perhaps the first field report from Indian soils that largely describes dual inoculation of Rhizobium sp. LSMR-32 and Enterococcus mundtii LSMRS-3 and the same can be considered as a game-changer approach to simultaneously induce salt tolerance and improve productivity in spring mungbean under saline stress conditions.

Using Genetic Engineering Techniques to Develop Banana Cultivars With Fusarium Wilt Resistance and Ideal Plant Architecture

Bananas (Musa spp.) are an important fruit crop worldwide. The fungus Fusarium oxysporum f. sp. cubense (Foc), which causes Fusarium wilt, is widely regarded as one of the most damaging plant diseases. Fusarium wilt has previously devastated global banana production and continues to do so today. In addition, due to the current use of high-density banana plantations, desirable banana varieties with ideal plant architecture (IPA) possess high lodging resistance, optimum photosynthesis, and efficient water absorption. These properties may help to increase banana production. Genetic engineering is useful for the development of banana varieties with Foc resistance and ideal plant architecture due to the sterility of most cultivars. However, the sustained immune response brought about by genetic engineering is always accompanied by yield reductions. To resolve this problem, we should perform functional genetic studies of the Musa genome, in conjunction with genome editing experiments, to unravel the molecular mechanisms underlying the immune response and the formation of plant architecture in the banana. Further explorations of the genes associated with Foc resistance and ideal architecture might lead to the development of banana varieties with both ideal architecture and pathogen super-resistance. Such varieties will help the banana to remain a staple food worldwide.

AhABI4s Negatively Regulate Salt-Stress Response in Peanut

Soil salinity is one of the major factors that limit the area of cultivable land and yield potential of crops. The ability of salt tolerance varies with plant species. Peanut (Arachis hypogaea L.) is a moderately salt-sensitive and economically important crop, however, their biological processes involved in salt-stress response remain unclear. In this study, we investigated the role of A. hypogaea L. ABSCISIC ACID INSENSITIVE 4s (AhABI4s) in salt tolerance and elucidated its mode of action in peanuts. The results showed that the downregulation of AhABI4s via whole plant virus-induced gene silencing has enhanced the survival rate, biomass accumulation, and root/shoot ratio of peanut seedlings in response to salt-stress. Transcriptomics, quantitative proteomics, and phosphoproteomic analyses were performed using AhABI4s-silenced and Mock plants. The expression pattern of 15,247 genes, 1,900 proteins, and 2,620 phosphorylation sites were affected by silencing of AhABI4s in peanut leaf and root after sodium chloride (NaCl) treatment. Among them, 63 potential downstream target genes of ABI4 changed consistently at both transcription and translation levels, and the protein/phosphorylation levels of 31 ion transporters/channels were also affected. Electrophoretic mobility shift assays (EMSA) showed that ABI4 was able to bind to the promoters of HSP70, fructokinase (FRK), and pyruvate kinase (PK) coding genes in vitro. In addition, we also detected a binding preference of AhABI4 for CACT(G/T)GCA motif in the promoters of down-regulated genes in peanut leaf. Collectively, the potential downstream targets which were regulated at the levels of transcription and translation, binding preference, and in vivo phosphorylation sites that had been revealed in this study will provide new insight into the AhABI4s-mediated salt tolerance regulation mechanism in peanuts.

Peptide-Based Polyion Complex Vesicles That Deliver Enzymes into Intact Plants To Provide Antibiotic Resistance without Genetic Modification

Direct delivery of enzymes into intact plants using cell-penetrating peptides (CPPs) is an attractive approach for modifying plant functions without genetic modification. However, by conventional methods, it is difficult to maintain the enzyme activity for a long time because of proteolysis of the enzymes under physiological conditions. Here, we developed a novel enzyme delivery system using polyion complex vesicles (PICsomes) to protect the enzyme from proteases. We created PICsome-bearing reactive groups at the surface by mixing an anionic block copolymer, alkyne-TEG-P(Lys-COOH), and a cationic peptide, P(Lys). The PICsome encapsulated neomycin phosphotransferase II (NPTII), a kanamycin resistance enzyme, and protected NPTII from proteases in vitro. A CPP-modified PICsome delivered NPTII into the root hair cells of Arabidopsis thaliana seedlings and provided kanamycin resistance in the seedlings that lasted for 7 days. Thus, the PICsome-mediated enzyme delivery system is a promising method for imparting long-term transient traits to plants without genetic modification.

Effects of Enterobacter cloacae HG-1 on the Nitrogen-Fixing Community Structure of Wheat Rhizosphere Soil and on Salt Tolerance

The present study investigated the physiological and biochemical characteristics of Enterobacter cloacae HG-1 isolated from saline-alkali soil. We further studied the effect of this strain on the salt tolerance of wheat and on the community structure of nitrogen-fixing bacteria in rhizosphere soil. We determined that the investigated strain had high nitrogen fixation activity and produced iron carriers, 1-aminocyclopropane-1-carboxylic acid deaminase, and plant hormones. The metabolites of this strain contained 2,3-butanediol, [R-(R*, R*)], 2-heptanone, and other growth-promoting and antibacterial substances. The strain was also highly salt-tolerant (10% NaCl). After the inoculation of wheat with the HG-1 strain, we recorded increases in root length, plant height, fresh weight, and dry weight of 19.15%, 18.83%, 16.67%, and 17.96%, respectively, compared with uninoculated plants (P < 0.05). Compared with the leaves of uninoculated plants, the proline concentration in the leaves of inoculated plants increased by 12.43% (P < 0.05), the malondialdehyde level decreased by 27.26% (P < 0.05), K+ increased by 20.69%, Ca2+ increased by 57.53% and Na+ decreased by 31.43% (all P<0.05). Furthermore, we detected that inoculation with the HG-1 strain did not affect the species composition of nitrogen-fixing bacteria in wheat rhizosphere soil at the phylum level. However, the average relative abundance of Proteobacteria was significantly increased, whereas the abundance of Verrucomiorobia was significantly decreased compared with uninoculated plants. At the genus level, we detected 32 genera in control samples and 27 genera in inoculated samples, and the species diversity and relative abundance of samples inoculated with the HG-1 strain decreased compared with uninoculated plants. Inoculated samples had lower abundances of Azospirillum, Rhodomicrobium, and Anabaena. Our study demonstrated that the inoculation of wheat with E. cloacae HG-1 could promote the growth of wheat under salt stress and increase salt stress tolerance. The results of this study investigating the interaction among soil, plants, and microorganisms supplement agricultural microbial databases and could provide a reference for the development of microbial-based saline soil improvement programs.

Root morphological response of six peanut cultivars to chromium (VI) toxicity

We investigated the hypothesis that root morphology plays a crucial role in the variation in chromium (Cr) accumulation among peanut (Arachis hypogaea L.) cultivars, using the relationship between Cr accumulation and morphological characteristics of six peanut cultivars determined under 0, 10, 25, 75, and 100 μmol L^-1 Cr(VI) via hydroponic experiment. Significant variations were observed in Cr accumulation and root morphological parameters among peanut cultivars at the five Cr levels. The Cr concentrations in plants exhibited 1.72-, 4.67-, 1.81-, and 2.91-fold variations within cultivars for 10, 25, 75, and 100 μmol L^-1 Cr treatments, respectively. Positive correlations were found for total Cr in plants with total root length (RL), root surface area (SA), and root volume (RV). Negative correlations were also observed between the percentages of Cr in shoots and specific root length. These results suggest that root system morphology may partly explain the variation in Cr accumulation among cultivars. Cultivars with greater RL, SA, and RV showed higher capability for Cr accumulation.

Expression of Single Chain Variable Fragment (scFv) Molecules in Plants: A Comprehensive Update

Single chain variable fragments (scFvs) are generated by joining together the variable heavy and light chain of a monoclonal antibody (mAb) via a peptide linker. They offer some advantages over the parental mAb such as low molecular weight, heterologous production, multimeric form, and multivalency. The scFvs were produced against more than 50 antigens till date using 10 different plant species as the expression system. There were considerable improvements in the expression and purification strategies of scFv in the last 24 years. With the growing demand of scFv in therapeutic and diagnostic fields, its biosynthesis needs to be increased. The easiness in development, maintenance, and multiplication of transgenic plants make them an attractive expression platform for scFv production. The review intends to provide comprehensive information about the use of plant expression system to produce scFv. The developments, advantages, pitfalls, and possible prospects of improvement for the exploitation of plants in the industrial level are discussed.

Comparative Transcriptome Analysis Reveals Molecular Defensive Mechanism of Arachis hypogaea in Response to Salt Stress

Abiotic stresses comprise all nonliving factors, such as soil salinity, drought, extreme temperatures, and metal toxicity, posing a serious threat to agriculture and affecting the plant production around the world. Peanut (Arachis hypogaea L.) is one of the most important crops for vegetable oil, proteins, minerals, and vitamins in the world. Therefore, it is of importance to understand the molecular mechanism of peanut against salt stress. Six transcriptome sequencing libraries including 24-hour salt treatments and control samples were constructed from the young leaves of peanut. A comprehensive analysis between two groups detected 3,425 differentially expressed genes (DEGs) including 2,013 upregulated genes and 1,412 downregulated genes. Of these DEGs, 141 transcription factors (TFs) mainly consisting of MYB, AP2/ERF, WRKY, bHLH, and HSF were identified in response to salinity stress. Further, GO categories of the DEGs highly related to regulation of cell growth, cell periphery, sustained external encapsulating structure, cell wall organization or biogenesis, antioxidant activity, and peroxidase activity were significantly enriched for upregulated DEGs. The function of downregulated DEGs was mainly enriched in regulation of metabolic processes, oxidoreductase activity, and catalytic activity. Fourteen DEGs with response to salt tolerance were validated by real-time PCR. Taken together, the identification of DEGs' response to salt tolerance of cultivated peanut will provide a solid foundation for improving salt-tolerant peanut genetic manipulation in the future.

Genome-wide identification of microsatellite markers from cultivated peanut (Arachis hypogaea L.)

Background

Microsatellites, or simple sequence repeats (SSRs), represent important DNA variations that are widely distributed across the entire plant genome and can be used to develop SSR markers, which can then be used to conduct genetic analyses and molecular breeding. Cultivated peanut (A. hypogaea L.), an important oil crop worldwide, is an allotetraploid (AABB, 2n = 4× = 40) plant species. Because of its complex genome, genomic marker development has been very challenging. However, sequencing of cultivated peanut genome allowed us to develop genomic markers and construct a high-density physical map.

Results

A total of 8,329,496 SSRs were identified, including 3,772,653, 4,414,961, and 141,882 SSRs that were distributed in subgenome A, B, and nine scaffolds, respectively. Based on the flanking sequences of the identified SSRs, a total of 973,984 newly developed SSR markers were developed in subgenome A (462,267), B (489,394), and nine scaffolds (22,323), with an average density of 392.45 markers per Mb. In silico PCR evaluation showed that an average of 88.32% of the SSR markers generated only one in silico-specific product in two tetraploid A. hypogaea varieties, Tifrunner and Shitouqi. A total of 39,599 common SSR markers were identified among the two A. hypogaea varieties and two progenitors, A. duranensis and A. ipaensis. Additionally, an amplification effectiveness of 44.15% was observed by real PCR validation. Moreover, a total of 1276 public SSR loci were integrated with the newly developed SSR markers. Finally, a previously known leaf spot quantitative trait locus (QTL), qLLS_T13_A05_7, was determined to be in a 1.448-Mb region on chromosome A05. In this region, a total of 819 newly developed SSR markers were located and 108 candidate genes were detected.

Conclusions

The availability of these newly developed and public SSR markers both provide a large number of molecular markers that could potentially be used to enhance the process of trait genetic analyses and improve molecular breeding strategies for cultivated peanut.

Halotolerant Rhizobacterial Strains Mitigate the Adverse Effects of NaCl Stress in Soybean Seedlings

BACKGROUND

Salinity is one of the major abiotic constraints that hinder health and quality of crops. Conversely, halotolerant plant growth-promoting rhizospheric (PGPR) bacteria are considered biologically safe for alleviating salinity stress.

RESULTS

We isolated halotolerant PGPR strains from the rhizospheric soil of Artemisia princeps, Chenopodium ficifolium, Echinochloa crus-galli, and Oenothera biennis plants; overall, 126 strains were isolated. The plant growth-promoting traits of these isolates were studied by inoculating them with the soil used to grow soybean plants under normal and salt stress (NaCl; 200 mM) conditions. The isolates identified as positive for growth-promoting activities were subjected to molecular identification. Out of 126 isolates, five strains-Arthrobacter woluwensis (AK1), Microbacterium oxydans (AK2), Arthrobacter aurescens (AK3), Bacillus megaterium (AK4), and Bacillus aryabhattai (AK5)-were identified to be highly tolerant to salt stress and demonstrated several plant growth-promoting traits like increased production of indole-3-acetic acid (IAA), gibberellin (GA), and siderophores and increased phosphate solubilization. These strains were inoculated in the soil of soybean plants grown under salt stress (NaCl; 200 mM) and various physiological and morphological parameters of plants were studied. The results showed that the microbial inoculation elevated the antioxidant (SOD and GSH) level and K+ uptake and reduced the Na+ ion concentration. Moreover, inoculation of these microbes significantly lowered the ABA level and increased plant growth attributes and chlorophyll content in soybean plants under 200 mM NaCl stress. The salt-tolerant gene GmST1 was highly expressed with the highest expression of 42.85% in AK1-treated plants, whereas the lowest expression observed was 13.46% in AK5-treated plants. Similarly, expression of the IAA regulating gene GmLAX3 was highly depleted in salt-stressed plants by 38.92%, which was upregulated from 11.26% to 43.13% upon inoculation with the microorganism.

CONCLUSION

Our results showed that the salt stress-resistant microorganism used in these experiments could be a potential biofertilizer to mitigate the detrimental effects of salt stress in plants via regulation of phytohormones and gene expression.

Effect of Drought Stress and Developmental Stages on Microbial Community Structure and Diversity in Peanut Rhizosphere Soil

Background: Peanut (Arachis hypogaea L.), an important oilseed and food legume, is widely cultivated in the semi-arid tropics. Drought is the major stress in this region which limits productivity. Microbial communities in the rhizosphere are of special importance to stress tolerance. However, relatively little is known about the relationship between drought and microbial communities in peanuts. Method: In this study, deep sequencing of the V3-V4 region of the 16S rRNA gene was performed to characterize the microbial community structure of drought-treated and untreated peanuts. Results: Taxonomic analysis showed that Actinobacteria, Proteobacteria, Saccharibacteria, Chloroflexi, Acidobacteria and Cyanobacteria were the dominant phyla in the peanut rhizosphere. Comparisons of microbial community structure of peanuts revealed that the relative abundance of Actinobacteria and Acidobacteria dramatically increased in the seedling and podding stages in drought-treated soil, while that of Cyanobacteria and Gemmatimonadetes increased in the flowering stage in drought-treated rhizospheres. Metagenomic profiling indicated that sequences related to metabolism, signaling transduction, defense mechanism and basic vital activity were enriched in the drought-treated rhizosphere, which may have implications for plant survival and drought tolerance. Conclusion: This microbial communities study will form the foundation for future improvement of drought tolerance of peanuts via modification of the soil microbes.

Antarctic Extremophiles: Biotechnological Alternative to Crop Productivity in Saline Soils

Salinization of soils is one of the main sources of soil degradation worldwide, particularly in arid and semiarid ecosystems. High salinity results in osmotic stress and it can negatively impact plant grow and survival. Some plant species, however, can tolerate salinity by accumulating osmolytes like proline and maintaining low Na+ concentrations inside the cells. Another mechanism of saline stress tolerance is the association with symbiotic microorganism, an alternative that can be used as a biotechnological tool in susceptible crops. From the immense diversity of plant symbionts, those found in extreme environments such as Antarctica seems to be the ones with most potential since they (and their host) evolved in harsh and stressful conditions. We evaluated the effect of the inoculation with a consortium of plant growth-promoting rhizobacteria (PGPB) and endosymbiotic fungi isolated from an Antarctic plant on saline stress tolerance in different crops. To test this we established 4 treatments: (i) uninoculated plants with no saline stress, (ii) uninoculated plants subjected to saline stress (200 mM NaCl), (iii) plants inoculated with the microorganism consortium with no saline stress, and (iv) inoculated plants subjected to saline stress. First, we assessed the effect of symbiont consortium on survival of four different crops (cayenne, lettuce, onion, and tomato) in order to obtain a more generalized response of this biological interaction. Second, in order to deeply the mechanisms involved in salt tolerance, in lettuce plants we measured the ecophysiological performance (Fv/Fm) and lipid peroxidation to estimate the impact of saline stress on plants. We also measured proline accumulation and NHX1 antiporter gene expression (involved in Na+ detoxification) to search for possible mechanism of stress tolerance. Additionally, root, shoot, and total biomass was also obtained as an indicator of productivity. Overall, plants inoculated with microorganisms from Antarctica increased the fitness related traits in several crops. In fact, three of four crops selected to assess the general response increased its survival under salt conditions compared with those uninoculated plants. On the other hand, saline stress negatively impacted all measured trait, but inoculated plants were significantly less affected. In control osmotic conditions, there were no differences in proline accumulation and lipid peroxidation between inoculation treatments. Interestingly, even in control salinity, Fv/Fm was higher in inoculated plants after 30 and 60 days. Under osmotic stress, Fv/Fm, proline accumulation and NHX1 expression was significantly higher and lipid peroxidation lower in inoculated plants compared to uninoculated individuals. Moreover, inoculated plants exposed to saline stress had a similar final biomass (whole plant) compared to individuals under no stress. We conclude that Antarctic extremophiles can effectively reduce the physiological impact of saline stress in a salt-susceptible crops and also highlight extreme environments such as Antarctica as a key source of microorganism with high biotechnological potential.

Plant Cellular and Molecular Biotechnology: Following Mariotti's Steps

This review is dedicated to the memory of Prof. Domenico Mariotti, who significantly contributed to establishing the Italian research community in Agricultural Genetics and carried out the first experiments of Agrobacterium-mediated plant genetic transformation and regeneration in Italy during the 1980s. Following his scientific interests as guiding principles, this review summarizes the recent advances obtained in plant biotechnology and fundamental research aiming to: (i) Exploit in vitro plant cell and tissue cultures to induce genetic variability and to produce useful metabolites; (ii) gain new insights into the biochemical function of Agrobacterium rhizogenes rol genes and their application to metabolite production, fruit tree transformation, and reverse genetics; (iii) improve genetic transformation in legume species, most of them recalcitrant to regeneration; (iv) untangle the potential of KNOTTED1-like homeobox (KNOX) transcription factors in plant morphogenesis as key regulators of hormonal homeostasis; and (v) elucidate the molecular mechanisms of the transition from juvenility to the adult phase in Prunus tree species.

Transgenic approaches for genetic improvement in groundnut (Arachis hypogaea L.) against major biotic and abiotic stress factors

Cultivated groundnut (Arachis hypogaea L.) is considered as one of the primary oilseed crops and a major fodder for cattle industry in most of the developing countries, owing to its rich source of protein. It is due to its geocarpic nature of growth that the overall yield performance of groundnut is hindered by several biotic and abiotic stress factors. Multidimensional attempts were undertaken to combat these factors by developing superior groundnut varieties, modified with integral mechanism of tolerance/resistance; however this approach proved to be futile, owing to inferior pod and kernel quality. As a superior alternative, biotechnological intervention like transformation of foreign genes, either directly (biolistic) or via Agrobacterium, significantly aided in the development of advanced groundnut genotypes equipped with integral resistance against stresses and enhanced yield attributing traits. Several genes triggered by biotic and abiotic stresses, were detected and some of them were cloned and transformed as major parts of transgenic programmes. Application of modern molecular biological techniques, in designing biotic and abiotic stress tolerant/resistant groundnut varieties that exhibited mechanisms of resistance, relied on the expression of specific genes associated to particular stress. The genetically transformed stress tolerant groundnut varieties possess the potential to be employed as donor parents in traditional breeding programmes for developing varieties that are resilient to fungal, bacterial, and viral diseases, as well as to draught and salinity. The present review emphasizes on the retrospect and prospect of genetic transformation tools, implemented for the enhancement of groundnut varieties against key biotic and abiotic stress factors.

Resistance to Thrips in Peanut and Implications for Management of Thrips and Thrips-Transmitted Orthotospoviruses in Peanut

Thrips are major pests of peanut (Arachis hypogaea L.) worldwide, and they serve as vectors of devastating orthotospoviruses such as Tomato spotted wilt virus (TSWV) and Groundnut bud necrosis virus (GBNV). A tremendous effort has been devoted to developing peanut cultivars with resistance to orthotospoviruses. Consequently, cultivars with moderate field resistance to viruses exist, but not much is known about host resistance to thrips. Integrating host plant resistance to thrips in peanut could suppress thrips feeding damage and reduce virus transmission, will decrease insecticide usage, and enhance sustainability in the production system. This review focuses on details of thrips resistance in peanut and identifies future directions for incorporating thrips resistance in peanut cultivars. Research on thrips-host interactions in peanut is predominantly limited to field evaluations of feeding damage, though, laboratory studies have revealed that peanut cultivars could differentially affect thrips feeding and thrips biology. Many runner type cultivars, field resistant to TSWV, representing diverse pedigrees evaluated against thrips in the greenhouse revealed that thrips preferred some cultivars over others, suggesting that antixenosis "non-preference" could contribute to thrips resistance in peanut. In other crops, morphological traits such as leaf architecture and waxiness and spectral reflectance have been associated with thrips non-preference. It is not clear if foliar morphological traits in peanut are associated with reduced preference or non-preference of thrips and need to be evaluated. Besides thrips non-preference, thrips larval survival to adulthood and median developmental time were negatively affected in some peanut cultivars and in a diploid peanut species Arachis diogoi (Hoehne) and its hybrids with a Virginia type cultivar, indicating that antibiosis (negative effects on biology) could also be a factor influencing thrips resistance in peanut. Available field resistance to orthotospoviruses in peanut is not complete, and cultivars can suffer substantial yield loss under high thrips and virus pressure. Integrating thrips resistance with available virus resistance would be ideal to limit losses. A discussion of modern technologies such as transgenic resistance, marker assisted selection and RNA interference, and future directions that could be undertaken to integrate resistance to thrips and to orthotospoviruses in peanut cultivars is included in this article.

Peanut (Arachis hypogaea L.): A Prospective Legume Crop to Offer Multiple Health Benefits Under Changing Climate

Peanut is a multipurpose oil-seed legume, which offer benefits in many ways. Apart from the peanut plant's beneficial effects on soil quality, peanut seeds are nutritious and medicinally and economically important. In this review, insights into peanut origin and its domestication are provided. Peanut is rich in bioactive components, including phenolics, flavonoids, polyphenols, and resveratrol. In addition, the involvement of peanut in biological nitrogen fixation is highly significant. Recent reports regarding peanut responses and N₂ fixation ability in response to abiotic stresses, including drought, salinity, heat stress, and iron deficiency on calcareous soils, have been incorporated. As a biotechnological note, recent advances in the development of transgenic peanut plants are also highlighted. In this context, regulation of transcriptional factors and gene transfer for the development of stress-tolerant peanut genotypes are of prime importance. Above all, this review signifies the importance of peanut cultivation and human consumption in view of the scenario of changing world climate in order to maintain food security.

Characterization of halotolerant, pigmented, plant growth promoting bacteria of groundnut rhizosphere and its in-vitro evaluation of plant-microbe protocooperation to withstand salinity and metal stress

The use of plant associated, indigenous beneficial microbes for sustainable agriculture is getting worldwide acceptance as they successfully colonize at different plant niche under stress conditions to enhance the crop productivity. They also generate several plant growth regulators and protect plants from adversity like presence of salts and metals. In the present study, indigenous, halotolerant, plant growth promoting (PGP) bacterial isolates were isolated from the saline rhizospheric soil of groundnut plants aiming to investigate its in-vitro metal remediation capabilities under saline stress condition. Two pigmented bacteria were selected based on their phenotypic, biochemical, physiological and PGP characters and identified as members of family Bacillaceae (Bacillus and Halobacillus) based on 16S rRNA gene sequence similarity. The pigments were extracted, tested for different antioxidant properties and identified by GC-MS and FT-IR spectra. Simultaneously, both strains exhibited a wide range of salinity (NaCl≥25%), metal resistance (Zinc≈1700mgkg^-1, Aluminium≈1800mgkg^-1, Lead≈1800mgkg^-1), pH (6-10), PGP attributes (indole - 1.05-3.15μgml^-1, ammonia - 0.13-19.95mmolml^-1, nitrite - 0.07-0.26mmolml^-1) and antibiotics sensitivity revealing their wide range of metabolic diversity. In-vitro inoculation of groundnut seedlings with selected isolates under salinity (1% NaCl) and metal (Zn, Al and Pb) stress had a positive impact on different plant physiological parameters (lesser lignification, intact proto xylem and cortical parenchyma) which was correlated with PGP attributes. Microwave plasma atomic emission spectroscopy analysis of seedling samples also detected less amount of metals in plants treated with bacteria indicating, an establishment of plant-microbe protocooperation to withstand salinity and metal stress. This strategy can be implemented to improve crop production in saline metal polluted agriculture fields.

Contribution of root uptake to cadmium accumulation in two peanut cultivars: evidence from a split-column soil experiment

Cadmium (Cd) accumulation and internal Cd translocation in the peanut (Arachis hypogaea L.) are highly related to root uptake, which may largely depend on the cultivar variation and the depth of the Cd-contaminated soil. A split-column soil experiment was conducted using two common Chinese peanut cultivars (Huayu-20 and Huayu-23) known to relocate Cd to different tissues. The growth medium was separated into four layers and Cd solution was solely applied to one layer to determine the key depth affecting the Cd accumulation in a plant via root uptakes. The results showed that the biomass of Huayu-23 was significantly higher biomass (3.28-94.0%) than that of Huayu-20, especially in the aerial parts (stems and leaves) and kernels, implying the dilution of Cd. Following the addition of Cd to the soil, the Cd concentrations in peanut tissues increased on average by 28.9-172 and 28.3-111% in Huayu-20 and Huayu-23, respectively. The largest presence of Cd in a peanut plant was observed in the aerial parts, followed by the kernels. Huayu-20 accumulated more Cd in plant tissues than did Huayu-23 due to the former's high Cd translocation. These findings imply that peanut cultivars vary widely in biomass, Cd accumulation, and the percentage distribution of Cd among various plant tissues, especially kernels. Different Cd treatments in the full depth of the root zone induced significant alterations in Cd accumulation of peanut tissues, especially kernels, for both cultivars. The percentage distribution of Cd accumulation by kernels was significantly higher in the deeper layer than in the top layer of the root zone for both peanut cultivars. This study suggests that soil modifications performed during agronomic activities should take into account the full depth of root exploration as well as the peanut cultivars to manage plant Cd uptake.

Genotype-independent and enhanced in planta Agrobacterium tumefaciens-mediated genetic transformation of peanut [Arachis hypogaea (L.)]

Agrobacterium infection and regeneration of the putatively transformed plant from the explant remains arduous for some crop species like peanut. Henceforth, a competent and reproducible in planta genetic transformation protocol is established for peanut cv. CO7 by standardizing various factors such as pre-culture duration, acetosyringone concentration, duration of co-cultivation, sonication and vacuum infiltration. In the present investigation, Agrobacterium tumefaciens strain EHA105 harboring the binary vector pCAMBIA1301-bar was used for transformation. The two-stage selection was carried out using 4 and 250 mg l^-1 BASTA^® to completely eliminate the chimeric and non-transformed plants. The transgene integration into plant genome was evaluated by GUS histochemical assay, polymerase chain reaction (PCR), and Southern blot hybridization. Among the various combinations and concentrations analyzed, highest transformation efficiency was obtained when the 2-day pre-cultured explants were subjected to sonication for 6 min and vacuum infiltrated for 3 min in Agrobacterium suspension, and co-cultivated on MS medium supplemented with 150 µM acetosyringone for 3 days. The fidelity of the standardized in planta transformation method was assessed in five peanut cultivars and all the cultivars responded positively with a transformation efficiency ranging from minimum 31.3% (with cv. CO6) to maximum 38.6% (with cv. TMV7). The in planta transformation method optimized in this study could be beneficial to develop superior peanut cultivars with desirable genetic traits.

Stress Inducible Overexpression of AtHDG11 Leads to Improved Drought and Salt Stress Tolerance in Peanut (Arachis hypogaea L.)

Peanut is an important oilseed and food legume cultivated as a rain-fed crop in semi-arid tropics. Drought and high salinity are the major abiotic stresses limiting the peanut productivity in this region. Development of drought and salt tolerant peanut varieties with improved yield potential using biotechnological approach is highly desirable to improve the peanut productivity in marginal geographies. As abiotic stress tolerance and yield represent complex traits, engineering of regulatory genes to produce abiotic stress-resilient transgenic crops appears to be a viable approach. In the present study, we developed transgenic peanut plants expressing an Arabidopsis homeodomain-leucine zipper transcription factor (AtHDG11) under stress inducible rd29A promoter. A stress-inducible expression of AtHDG11 in three independent homozygous transgenic peanut lines resulted in improved drought and salt tolerance through up-regulation of known stress responsive genes (LEA, HSP70, Cu/Zn SOD, APX, P5CS, NCED1, RRS5, ERF1, NAC4, MIPS, Aquaporin, TIP, ELIP) in the stress gene network, antioxidative enzymes, free proline along with improved water use efficiency traits such as longer root system, reduced stomatal density, higher chlorophyll content, increased specific leaf area, improved photosynthetic rates, and increased intrinsic instantaneous WUE. Transgenic peanut plants displayed high yield compared to non-transgenic plants under both drought and salt stress conditions. Holistically, our study demonstrates the potentiality of stress-induced expression of AtHDG11 to improve the drought, salt tolerance in peanut.

Mining Halophytes for Plant Growth-Promoting Halotolerant Bacteria to Enhance the Salinity Tolerance of Non-halophytic Crops

Salinity stress is one of the major abiotic stresses limiting crop production in arid and semi-arid regions. Interest is increasing in the application of PGPRs (plant growth promoting rhizobacteria) to ameliorate stresses such as salinity stress in crop production. The identification of salt-tolerant, or halophilic, PGPRs has the potential to promote saline soil-based agriculture. Halophytes are a useful reservoir of halotolerant bacteria with plant growth-promoting capabilities. Here, we review recent studies on the use of halophilic PGPRs to stimulate plant growth and increase the tolerance of non-halophytic crops to salinity. These studies illustrate that halophilic PGPRs from the rhizosphere of halophytic species can be effective bio-inoculants for promoting the production of non-halophytic species in saline soils. These studies support the viability of bioinoculation with halophilic PGPRs as a strategy for the sustainable enhancement of non-halophytic crop growth. The potential of this strategy is discussed within the context of ensuring sustainable food production for a world with an increasing population and continuing climate change. We also explore future research needs for using halotolerant PGPRs under salinity stress.

A Growth-Promoting Bacteria, Paenibacillus yonginensis DCY84T Enhanced Salt Stress Tolerance by Activating Defense-Related Systems in Panax ginseng

Panax ginseng (C.A. Mayer) is a well-known medicinal plant used in traditional medicine in Korea that experiences serious salinity stress related to weather changes or incorrect fertilizer application. In ginseng, the use of Paenibacillus yonginensis DCY84^T to improve salt stress tolerance has not been thoroughly explored. Therefore, we studied the role of P. yonginensis DCY84^T under short-term and long-term salinity stress conditions in a controlled environment. In vitro testing of DCY84^T revealed high indole acetic acid (IAA) production, siderophore formation, phosphate solubilization and anti-bacterial activity. We determined that 10-min dip in 10¹⁰ CFU/ml DCY84^T was sufficient to protect ginseng against short-term salinity stress (osmotic stress) upon exposure to 300 mM NaCl treatment by enhancing nutrient availability, synthesizing hydrolyzing enzymes and inducing osmolyte production. Upon exposure to salinity stress (oxidative and ionic stress), strain DCY84^T-primed ginseng seedlings were protected by the induction of defense-related systems such as ion transport, ROS scavenging enzymes, proline content, total sugars, and ABA biosynthetic genes, as well as genes involved in root hair formation. Additionally, ginseng primed with DCY84^T and exposed to 300 mM NaCl showed the same metabolite profile as control ginseng plants, suggesting that DCY84^T effectively reduced salt stress. These results indicated that DCY84^T can be widely used as a microbial inoculant to protect ginseng plants against salinity stress conditions.

Genome-Wide Discovery of Microsatellite Markers from Diploid Progenitor Species, Arachis duranensis and A. ipaensis, and Their Application in Cultivated Peanut (A. hypogaea)

Despite several efforts in the last decade toward development of simple sequence repeat (SSR) markers in peanut, there is still a need for more markers for conducting different genetic and breeding studies. With the effort of the International Peanut Genome Initiative, the availability of reference genome for both the diploid progenitors of cultivated peanut allowed us to identify 135,529 and 199,957 SSRs from the A (Arachis duranensis) and B genomes (Arachis ipaensis), respectively. Genome sequence analysis showed uneven distribution of the SSR motifs across genomes with variation in parameters such as SSR type, repeat number, and SSR length. Using the flanking sequences of identified SSRs, primers were designed for 51,354 and 60,893 SSRs with densities of 49 and 45 SSRs per Mb in A. duranensis and A. ipaensis, respectively. In silico PCR analysis of these SSR markers showed high transferability between wild and cultivated Arachis species. Two physical maps were developed for the A genome and the B genome using these SSR markers, and two reported disease resistance quantitative trait loci (QTLs), qF2TSWV5 for tomato spotted wilt virus (TSWV) and qF2LS6 for leaf spot (LS), were mapped in the 8.135 Mb region of chromosome A04 of A. duranensis. From this genomic region, 719 novel SSR markers were developed, which provide the possibility for fine mapping of these QTLs. In addition, this region also harbors 652 genes and 49 of these are defense related genes, including two NB-ARC genes, three LRR receptor-like genes and three WRKY transcription factors. These disease resistance related genes could contribute to resistance to viral (such as TSWV) and fungal (such as LS) diseases in peanut. In summary, this study not only provides a large number of molecular markers for potential use in peanut genetic map development and QTL mapping but also for map-based gene cloning and molecular breeding.

Ex vitro hairy root induction in detached peanut leaves for plant-nematode interaction studies

BACKGROUND

Peanut (Arachis hypogaea) production is largely affected by a variety of abiotic and biotic stresses, including the root-knot nematode (RKN) Meloidogyne arenaria that causes yield losses worldwide. Transcriptome studies of wild Arachis species, which harbor resistance to a number of pests and diseases, disclosed several candidate genes for M. arenaria resistance. Peanut is recalcitrant to genetic transformation, so the use of Agrobacterium rhizogenes-derived hairy roots emerged as an alternative for in-root functional characterization of these candidate genes.

RESULTS

The present report describes an ex vitro methodology for hairy root induction in detached leaves based on the well-known ability of peanut to produce roots spontaneously from its petiole, which can be maintained for extended periods under high-humidity conditions. Thirty days after infection with the A. rhizogenes 'K599' strain, 90% of the detached leaves developed transgenic hairy roots with 5 cm of length in average, which were then inoculated with M. arenaria. For improved results, plant transformation, and nematode inoculation parameters were adjusted, such as bacterial cell density and growth stage; moist chamber conditions and nematode inoculum concentration. Using this methodology, a candidate gene for nematode resistance, AdEXLB8, was successfully overexpressed in hairy roots of the nematode-susceptible peanut cultivar 'Runner', resulting in 98% reduction in the number of galls and egg masses compared to the control, 60 days after M. arenaria infection.

CONCLUSIONS

This methodology proved to be more practical and cost-effective for functional validation of peanut candidate genes than in vitro and composite plant approaches, as it requires less space, reduces analysis costs and displays high transformation efficiency. The reduction in the number of RKN galls and egg masses in peanut hairy roots overexpressing AdEXLB8 corroborated the use of this strategy for functional characterization of root expressing candidate genes. This approach could be applicable not only for peanut-nematode interaction studies but also to other peanut root diseases, such as those caused by fungi and bacteria, being also potentially extended to other crop species displaying similar petiole-rooting competence.

Growth promotion of peanut (Arachis hypogaea L.) and maize (Zea mays L.) plants by single and mixed cultures of efficient phosphate solubilizing bacteria that are tolerant to abiotic stress and pesticides

The aims of this study were, to analyze in vitro phosphate solubilization activity of six native peanut bacteria and to determine the effect of single and mixed inoculation of these bacteria on peanut and maize plants. Ability to produce organic acids and cofactor PQQ, to solubilize FePO₄ and AlPO₄ and phosphatase activity were analyzed. Also, the ability to solubilize phosphate under abiotic stress and in the presence of pesticides of the selected bacteria was determined. The effect of single and mixed bacterial inocula was analyzed on seed germination, maize plant growth and in a crop rotation plant assay with peanut and maize. The six strains produced gluconic acid and five released cofactor PQQ into the medium. All bacteria showed ability to solubilize phosphate from FePO₄ and AlPO₄ and phosphatase activity. The ability of the bacteria to solubilize tricalcium phosphate under abiotic stress and in presence of pesticides indicated encouraging results. Bacterial inoculation on peanut and maize increased seed germination, plant́s growth and P content. Phosphate solubilizing bacteria used in this study showed efficient phosphate mineralizing and solubilization ability and would be potential P-biofertilizers for peanut and maize.

Halotolerant Rhizobacteria Promote Growth and Enhance Salinity Tolerance in Peanut

Use of Plant growth promoting rhizobacteria (PGPR) is a promising strategy to improve the crop production under optimal or sub-optimal conditions. In the present study, five diazotrophic salt tolerant bacteria were isolated from the roots of a halophyte, Arthrocnemum indicum. The isolates were partially characterized in vitro for plant growth promoting traits and evaluated for their potential to promote growth and enhanced salt tolerance in peanut. The 16S rRNA gene sequence homology indicated that these bacterial isolates belong to the genera, Klebsiella, Pseudomonas, Agrobacterium, and Ochrobactrum. All isolates were nifH positive and able to produce indole -3-acetic acid (ranging from 11.5 to 19.1 μg ml-1). The isolates showed phosphate solubilisation activity (ranging from 1.4 to 55.6 μg phosphate /mg dry weight), 1-aminocyclopropane-1-carboxylate deaminase activity (0.1 to 0.31 μmol α-kB/μg protein/h) and were capable of reducing acetylene in acetylene reduction assay (ranging from 0.95 to 1.8 μmol C2H4 mg protein/h). These isolates successfully colonized the peanut roots and were capable of promoting the growth under non-stress condition. A significant increase in total nitrogen (N) content (up to 76%) was observed over the non-inoculated control. All isolates showed tolerance to NaCl ranging from 4 to 8% in nutrient broth medium. Under salt stress, inoculated peanut seedlings maintained ion homeostasis, accumulated less reactive oxygen species (ROS) and showed enhanced growth compared to non-inoculated seedlings. Overall, the present study has characterized several potential bacterial strains that showed an enhanced growth promotion effect on peanut under control as well as saline conditions. The results show the possibility to reduce chemical fertilizer inputs and may promote the use of bio-inoculants.

Cadmium re-distribution from pod and root zones and accumulation by peanut (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) genotypes may differ greatly with regard to cadmium (Cd) accumulation, but the underlying mechanisms remain unclear. To determine the key factors that may contribute to Cd re-distribution and accumulation in peanut genotypes with different Cd accumulating patterns, a split-pot soil experiment was conducted with three common Chinese peanut cultivars (Fenghua-6, Huayu-20, and Huayu-23). The growth medium was separated into pod and root zones with varied Cd concentrations in each zone to determine the re-distribution of Cd after it is taken up via different routes. The peanut cultivars were divided into two groups based on Cd translocation efficiency as follows: (1) high internal Cd translocation efficiency cultivar (Fenghua-6) and (2) low internal Cd translocation efficiency cultivars (Huayu-20 and Huayu-23). Compared with Fenghua-6, low Cd translocation cultivars Huayu-20 and Huayu-23 showed higher biomass production, especially in stems and leaves, leading to dilution of metal concentrations. Results also showed that Cd concentration in roots increased significantly with increasing Cd concentrations in soils when Cd was applied in the root zone. However, there were no significant differences in the root Cd concentrations between different pod zone Cd treatments and the control, suggesting that root uptake, rather than pod uptake, is responsible for Cd accumulation in the roots of peanuts. Significant differences of Cd distribution were observed between pod and root zone Cd exposure treatments. The three peanut cultivars revealed higher kernel over total Cd fractions for pod than for root zone Cd exposure if only extra applied Cd was considered. This suggests that uptake through peg and pod shell might, at least partially, be responsible for the variation in Cd re-distribution and accumulation among peanut cultivars. Cd uptake by plants via two routes (i.e., via roots and via pegs and pods, respectively) and internal Cd translocation appear to be important mechanisms in determining Cd accumulation in the kernels of peanuts.

Stress Inducible Expression of AtDREB1A Transcription Factor in Transgenic Peanut (Arachis hypogaea L.) Conferred Tolerance to Soil-Moisture Deficit Stress

Peanut, an important oilseed crop, is gaining priority for the development of drought tolerant genotypes in recent times, since the area under drought is constantly on the rise. To achieve this, one of the important strategies is to genetically engineer the ruling peanut varieties using transcription factor regulating the expression of several downstream, abiotic-stress responsive gene(s). In this study, eight independent transgenic peanut (cv. GG20) lines were developed using AtDREB1A gene, encoding for a transcription factor, through Agrobacterium-mediated genetic transformation. The transgene insertion was confirmed in (T0) using PCR and Dot-blot analysis, while copy-number(s) was ascertained using Southern-blot analysis. The inheritance of AtDREB1A gene in individual transgenic plants (T1 and T2) was confirmed using PCR. In homozygous transgenic plants (T2), under soil-moisture deficit stress, elevated level of AtDREB1A transgene expression was observed by RT-PCR assay. The transgenic plants at 45-d or reproductive growth stage showed tolerance to severe soil-moisture deficit stress. Physio-biochemical parameters such as proline content, osmotic potential, relative water content, electrolytic leakage, and total-chlorophyll content were found positively correlated with growth-related traits without any morphological abnormality, when compared to wild-type. qPCR analysis revealed consistent increase in expression of AtDREB1A gene under progressive soil-moisture deficit stress in two homozygous transgenic plants. The transgene expression showed significant correlation with improved physio-biochemical traits. The improvement of drought-stress tolerance in combination with improved growth-related traits is very essential criterion for a premium peanut cultivar like GG20, so that marginal farmers of India can incur the economic benefits during seasonal drought and water scarcity.