Hong Ding

Background: Peanuts (Arachis hypogaea L.) cultivated in saline-alkali areas frequently endure drought stress. Yet, mechanistic research on combined salt–drought stress for peanut growth and yield remains scarce. Methods: A pot culture experiment was conducted to investigate the impacts of short-term drought imposed at the flowering stage on peanuts grown in saline-alkali soil. We comprehensively assessed peanut agronomic traits, cell ultrastructure, physicochemical properties, hormone change, rhizobacterial community, and rhizosphere soil metabolic profiles between single salt stress and salt and drought co-stress. Results: Our study reveals that co-stress markedly suppressed peanut yield, with 100-pod weight, 100-seed weight, pods per plant, and pod yield per plant reduced by 3.16%, 12.79%, 16.65%, and 22.14% relative to salt-only treatment. Combined stress triggered more severe ultrastructural alterations, cell wall degradation, and tissue deformation. It also degraded soil quality by lowering available phosphorus, alkaline hydrolyzable nitrogen, and available potassium. Meanwhile, co-stress reduced the relative abundance of nitrogen-cycling and plant growth-promoting rhizobacteria, alongside depleted beneficial sugar metabolites in rhizosphere soil. These shifts jointly constrain peanut growth and productivity. Conclusions: Thus, it is imperative to implement timely irrigation practices to avoid drought during peanut cultivation in saline-alkali areas, particularly during the flowering stage.

Leaf nitrogen allocation and photosynthetic proteins response can affect net photosynthetic rate (Pn), ultimately influencing crop yield under diverse environmental stresses. However, the internal relationship between Pn with leaf nitrogen allocation and photosynthetic proteins response under nitrogen or water scarcity in peanut (Arachis hypogaea L.) remains elusive. Here, comprehensive physiological property and proteomic analyses of peanut were conducted, revealing that both nitrogen and water scarcity remarkably impeded leaf growth and reduced Pn. Nitrogen deficiency significantly reduced the total nitrogen content per unit leaf area (Narea), chlorophyll content, and Pn, whereas drought stress caused a greater decline in photosynthetic nitrogen use efficiency (PNUE). The allocation of leaf nitrogen to photosynthetic components, including the carboxylation system and electron transport system in leaves, was significantly reduced when subjected to individual or combined deficiency. Proteomic analyses exhibited that several key photosynthetic proteins underwent a decrease under both single and combined water and nitrogen deficiency conditions. Thereby, Pn may decline due to the disruption of nitrogen allocation and down-regulated expression of photosynthetic proteins under these stress conditions. Our findings establish a benchmark for future research exploring the roles of leaf nitrogen allocation and photosynthetic proteins in the plant’s response to nitrogen or water deficiency.

Peanut (Arachis hydropoaea L.) demonstrates a prominent adaptability to diverse soil types. However, the specific effects of soil types on peanut growth and bacterial communities remain elusive. This study conducted a thorough examination of the agronomic traits, the corresponding physicochemical properties, and bacterial structure of rhizosphere soil in acidic (AT), neutral (NT), and saline–alkali (ST) soils, elucidating the internal relationship between soil type and peanut yield. Our results showed that different soil types exhibited significant differences in peanut yield, with ST demonstrating the lowest yield per plant, showing an 85.05% reduction compared to NT. Furthermore, available phosphorus content, urease, and invertase activities were substantially reduced in both ST and AT, particularly in ST by 95.35%, 38.57%, and 62.54%, respectively. Meanwhile, metagenomic sequencing unveiled a notable decline in Bradyrhizobium and Streptomyces in these soils, which is crucial for soil improvement. Further metabolic pathway analysis revealed that the reduction in pathways related to soil remediation, fertility improvement, and stress response in AT and ST may lead to slower peanut growth. In conclusion, peanuts cultivated in acidic and saline–alkali soils can increase yield via implementing soil management practices such as improving soil quality and refining micro-environments. Our study provides practical applications for enhancing peanut yield in low- to medium-yield fields.

Water and fertilizer application strategies seriously affect the healthy growth of peanuts. The stoichiometric ratio can directly reflect the elemental requirements for crop growth, which are very important for improving fertilizer utilization efficiency. In order to investigate the response of C (carbon), N (nitrogen), and P (phosphorus) allocation pattern and stoichiometric characteristics in peanut seedlings to water and nitrogen addition, we designed a greenhouse pot experiment which had different water treatments (W1, 75–80% field capacity; W2, 45–50% field capacity) and nitrogen addition treatments (N0, 0 kg hm⁻²; N1, 90 kg hm⁻²; N2, 180 kg hm⁻²). The distribution and content changes in C, N, and P in different organs were measured and analyzed by ecological stoichiometry. The results showed that drought stress significantly increased the N or P content of different organs. The average N/P value of peanut roots treated with W2 decreased by 13.02% compared to W1. Restoring irrigation relieved this stress while reducing the C/N and C/P of roots, stems, and leaves, as well as the N/P of roots and stems. The water treatment after rehydration showed significant differences in the C/N, C/P, and N/P ratios of peanut roots. The average values of the C/N, C/P, and N/P ratios of peanut roots in W2 treatment were reduced by 13.54%, 28.66%, and 16.34%, respectively, compared to W1 treatment. On the other hand, nitrogen application significantly increased the N content of stems and leaves, while reducing C/N. On the contrary, it significantly reduced the P content of roots and stems, and increased the N/P ratio of roots, stems, and leaves. Overall, there is a significant interaction between water and nitrogen treatment on the stoichiometric characteristics of C, N, and P in different organs, with water treatment playing a dominant role. In terms of nutrient distribution in organs, the average N content in leaves is the highest. The coefficient of variation (CV) of P content is greater than that of C and N content. The CV of N content, P content, and C/N and N/P ratios of the stem are all greater than those of the roots or leaves, while the stems are more sensitive to water and nitrogen conditions. And the N and P content of roots, stems, and leaves were positively correlated. Meanwhile, peanut seedlings have the phenomenon of ionic synergism that occurs between nitrogen and phosphorus ions. In summary, studying the stoichiometric ratios can reflect the water and fertilizer demand status of peanuts, thereby better improving water and fertilizer utilization efficiency.

Peanuts grown in saline alkali soil are also subjected to drought stress caused by water scarcity. Therefore, we used HY25 (peanut variety) as an experimental material to investigate the effects of drought on the height of peanut main stems, length of the first lateral branch, leaf area per plant, SPAD value, net photosynthetic rate, and accumulation and distribution of photosynthetic products in saline alkali soil. The results showed that the combined stress of short-term drought and salt significantly reduced the main stem height, first lateral branch length, single plant leaf area, SPAD value, net photosynthetic rate (Pn), intercellular carbon dioxide concentration (Ci), and dry matter accumulation of peanuts, including a decrease in single plant pod yield, 100-pod weight, 100-kernel weight, and peanut yield. And the impact of drought stress on peanut yield varies at different growth stages. For example, under drought stress alone, the sensitive period is the 40th day after planting (40D) > 60th day after planting (60D) > 30th day after planting (30D). Short-term drought has the greatest impact on peanut yield at 40D, while in contrast, resuming watering after drought at 30D results in a slight but not significant increase in peanut yield in comparison with the control. Under the combined stress of drought and salt, the sensitive period of peanuts was 40D > 30D > 60D, and the single pod weight of peanuts was significantly reduced by 15.26% to 57.60% from the flowering stage to the pod stage under drought treatment compared to salt treatment, indicating a significant interaction between drought and salt stress, reducing the single leaf area and net photosynthetic rate of peanut leaves, ultimately leading to a decrease in peanut yield. Therefore, when planting peanuts in saline alkali soil, drought should be avoided, especially early drought, in order to prevent the combined effects of drought and salt stress from harming peanut yield.

The yield and quality of peanut (Arachis hypogaea L.), an oil crop planted worldwide, are often limited by drought stress (DS) and nitrogen (N) deficiency. To investigate the molecular mechanism by which peanut counteracts DS and N deficiency, we conducted comprehensive transcriptomic and metabolomic analyses of peanut leaves. Herein, 829 known differentially accumulated metabolites, 324 differentially expressed transcription factors, and 5294 differentially expressed genes (DEGs) were identified under different water and N conditions. The transcriptome analysis demonstrated that drought-related DEGs were predominantly expressed in “glycolysis/gluconeogenesis” and “glycerolipid metabolism”, while N-deficiency-related DEGs were mainly expressed in starch and sucrose metabolism, as well as in the biosynthesis of amino acid pathways. The biosynthesis, transport, and catabolism of secondary metabolites accounted for a large proportion of the 1317 DEGs present in water and N co–limitation. Metabolomic analysis showed that the metabolic accumulation of these pathways was significantly dependent on the stress conditions. Additionally, the roles of metabolites and genes in these pathways, such as the biosynthesis of amino acids and phenylpropanoid biosynthesis under different stress conditions, were discussed. The results demonstrated that different genes, metabolic pathways, and metabolites were related to DS and N deficiency. Thus, this study elucidates the metabolic pathways and functional genes that can be used for the improvement of peanut resistance to abiotic stress.

To characterize the peanut rhizosphere bacteria community in response to salt stress, a pot experiment was performed with different salt concentrations. The peanut rhizosphere soils at flowering and mature stages were sampled to extract DNA for constructing bacterial 16S rRNA gene library, and then high-throughput sequencing was performed for sequencing and bioinformatics analysis. The results showed that Proteobacteria, Actinobacteria, Patescibacteria, Acidobacteria, and Chloroflexi were the dominant phyla, and the orders Saccharimonadales, Betaproteobacteria, Sphingomonadales, Gemmatimonadales, and Rhizobiales were dominated in the peanut rhizosphere soils. Comparisons of the bacterial community structure of peanuts revealed that the relative abundance of Proteobacteria dramatically increased, while that of Actinobacteria decreased in salt-treated soils, and the fluctuation increased with the increase of the salt concentration. Moreover, applying calcium fertilizer under salt stress increased the abundance of Betaproteobacteria, Gemmatimonadales, and Sphingomonadales, which were affected by salt stress, growth stages, and exogenous calcium application. Cluster analysis revealed that the dominant bacteria of soil groups with high salt concentration were similar and clustered together, while the soil samples of the same growth period were similar and clustered together according to the bacterial structure at the genus level under non-salt stress conditions. Bacterial community structure differed in the growth stages and soil salt concentrations, whereas the differences of soil groups with or without calcium application were relatively small. Function prediction analysis indicated that the sequences related to secondary metabolites, glycan biosynthesis and metabolism, and amino acid and lipid metabolism were enriched in high salt-treated soils. The functional groups increased significantly during the fast-growth period, low salt stress, and basal calcium fertilizer treatments, which may play an important role on the growth and stress response in peanut. This study of microbial communities could lay the foundation for future improvement of stress tolerance of peanuts via modification of the soil microbes.

Background: Long noncoding RNAs (lncRNAs), which are typically > 200 nt in length, are involved in numerous biological processes. Studies on lncRNAs in the cultivated peanut (Arachis hypogaea L.) largely remain unknown. Results: A genome-wide scan of the peanut (Arachis hypogaea L.) transcriptome identified 1442 lncRNAs, which were encoded by loci distributed over every chromosome. Long intergenic noncoding RNAs accounted for 85.58% of these lncRNAs. Additionally, 189 lncRNAs were differentially abundant in the root, leaf, or seed. Generally, lncRNAs showed lower expression levels, tighter tissue-specific expression, and less splicing than mRNAs. Approximately 44.17% of the lncRNAs with an exon/intron structure were alternatively spliced; this rate was slightly lower than the splicing rate of mRNA. Transcription at the start site event was the alternative splicing (AS) event with the highest frequency (28.05%) in peanut lncRNAs, whereas the occurrence rate (30.19%) of intron retention event was the highest in mRNAs. AS changed the target gene profiles of lncRNAs and increased the diversity and flexibility of lncRNAs, which may be important for lncRNAs to execute their functions. Additionally, a substantial number of the peanut AS isoforms generated from protein-encoding genes appeared to be noncoding because they were truncated transcripts; such isoforms can be legitimately regarded as a class of lncRNAs. The predicted target genes of the lncRNAs were involved in a wide range of biological processes. Furthermore, expression pattern of several selected lncRNAs and their target genes were examined under salt stress, results showed that all of them could respond to salt stress in different manners. Conclusions: This study provided a resource of candidate lncRNAs and expression patterns across tissues, and whether these lncRNAs are functional will be further investigated in our subsequent experiments.

Background: Exposure of seeds to high salinity can cause reduced germination and poor seedling establishment. Improving the salt tolerance of peanut (Arachis hypogaea L.) seeds during germination is an important breeding goal of the peanut industry. Bacterial communities in the spermosphere soils may be of special importance to seed germination under salt stress, whereas extant results in oilseed crop peanut are scarce. Methods: Here, bacterial communities colonizing peanut seeds with salt stress were characterized using 16S rRNA gene sequencing. Results: Peanut spermosphere was composed of four dominant genera: Bacillus, Massilia, Pseudarthrobacter, and Sphingomonas. Comparisons of bacterial community structure revealed that the beneficial bacteria (Bacillus), which can produce specific phosphatases to sequentially mineralize organic phosphorus into inorganic phosphorus, occurred in relatively higher abundance in salt-treated spermosphere soils. Further soil enzyme activity assays showed that phosphatase activity increased in salt-treated spermosphere soils, which may be associated with the shift of Bacillus. Conclusion: This study will form the foundation for future improvement of salt tolerance of peanuts at the seed germination stage via modification of the soil microbes.

Fatty acyl-acyl thioesterases (FATs), which hydrolyze the thioester bond linking acyl chains to an acyl carrier protein, thereby terminating their elongation, contribute significantly to the fatty acid (FA) content and composition of seed storage lipids. The peanut (Arachis hypogaea L.) genome was found to harbor 21 FAT (AhFAT) genes, distributed over 12 of the 20 chromosomes. The length of their predicted translation products varied from 74 to 415 residues, and all but one included the 1–2 Acyl-ACP_TE conserved domains. All of the coding sequences were interrupted by at least one intron, with the exon number ranging from two to 12, and five of the genes were liable to alternative splicing. When the RNA-Seq platform was used to assess the transcriptional behavior of the 21 AhFAT genes, transcription of only 13 was detectable in samples of root, leaves, and developing seed; among these, six were transcribed throughout the plant, three were root-specific and one was leaf-specific. A detailed analysis of a pair of homologous AhFATs showed that the coding region of each was split into six exons and that both were transcribed in all of the plant organs surveyed (although the intensity of their transcription was not the same in immature seed). The product of both genes was deposited in the chloroplast outer membrane. The constitutive expression of these genes in either yeast or Arabidopsis thaliana increased the FA content, especially that of saturated FAs. In peanut genome, 21 AhFAT genes were found and two of them were transformed into yeast and Arabidopsis for function identification. Results showed that overexpression of these two genes could increase the FA content, especially the saturated FAs content.