Identification of Quantitative Trait Nucleotides and Development of Diagnostic Markers for Nine Fatty Acids in the Peanut

The cultivated peanut (Arachis hypogaea L.) is an important oilseed crop worldwide, and fatty acid composition is a major determinant of peanut oil quality. In the present study, we conducted a genome-wide association study (GWAS) for nine fatty acid traits using the whole genome sequences of 160 representative Chinese peanut landraces and identified 6-1195 significant SNPs for different fatty acid contents. Particularly for oleic acid and linoleic acid, two peak SNP clusters on Arahy.09 and Arahy.19 were found to contain the majority of the significant SNPs associated with these two fatty acids. Additionally, a significant proportion of the candidate genes identified on Arahy.09 overlap with those identified in early studies, among which three candidate genes are of special interest. One possesses a significant missense SNP and encodes a known candidate gene FAD2A. The second gene is the gene closest to the most significant SNP for linoleic acid. It codes for an MYB protein that has been demonstrated to impact fatty acid biosynthesis in Arabidopsis. The third gene harbors a missense SNP and encodes a JmjC domain-containing protein. The significant phenotypic difference in the oleic acid/linoleic acid between the genotypes at the first and third candidate genes was further confirmed with PARMS analysis. In addition, we have also identified different candidate genes (i.e., Arahy.ZV39IJ, Arahy.F9E3EA, Arahy.X9ZZC1, and Arahy.Z0ELT9) for the remaining fatty acids. Our findings can help us gain a better understanding of the genetic foundation of peanut fatty acid contents and may hold great potential for enhancing peanut quality in the future.

Integrative Metabolic and Transcriptomic Profiling in Camellia oleifera and Camellia meiocarpa Uncover Potential Mechanisms That Govern Triacylglycerol Degradation during Seed Desiccation

Camellia seed oil is a top-end quality of cooking oil in China. The oil quality and quantity are formed during seed maturation and desiccation. So far, it remains largely unresolved whether lipid degradation occurs and contributes to Camellia oil traits. In this study, three different Camellia germplasms, C. oleifera cv. Min 43 (M43), C. meiocarpa var. Qingguo (QG), and C. meiocarpa cv Hongguo (HG) were selected, their seed oil contents and compositions were quantified across different stages of seed desiccation. We found that at the late stage of desiccation, M43 and QG lost a significant portion of seed oil, while such an event was not observed in HG. To explore the molecular bases for the oil loss In M43, the transcriptomic profiling of M43 and HG was performed at the early and the late seed desiccation, respectively, and differentially expressed genes (DEGs) from the lipid metabolic pathway were identified and analyzed. Our data demonstrated that different Camellia species have diverse mechanisms to regulate seed oil accumulation and degradation, and that triacylglycerol-to-terpenoid conversion could account for the oil loss in M43 during late seed desiccation.

Enhancing the accumulation of linoleic acid and α-linolenic acid through the pre-harvest ethylene treatment in Camellia oleifera

Camellia oleifera Abel. (C. oleifera) is an important woody edible oil tree species in China. The quality of C. oleifera oil (tea oil) is mainly determined by the contents of linoleic acid (LA) and α-linolenic acid (ALA). However, how to increase the contents of LA and ALA in tea oil and the corresponding regulating mechanism have not been clarified. In the present study, we found that the LA and ALA contents in C. oleifera seeds were significant positively associated with the concentrations of ethephon and were decreased by ethylene inhibitor treatment. Furthermore, 1.5 g L^-1 ethephon could receive an optimal LA and ALA contents without adverse effects to the growth of 'Huashuo' trees in this study. The ethephon treatment also increased the contents of 1-aminocyclopropane-1-carboxylic acid (ACC), sucrose, soluble sugar and reducing sugar contents in seeds. Transcriptome analysis further suggested that exogenous ethephon application enhanced the accumulation of LA and ALA via regulating genes involved in LA and ALA metabolism, plant hormone signal transduction pathways, and starch and sucrose metabolism. Our findings confirm the role of ethylene in LA and ALA regulation and provide new insights into the potential utilization of ethylene as a LA and ALA inducer in C. oleifera cultivation.

Insights into the Novel FAD2 Gene Regulating Oleic Acid Accumulation in Peanut Seeds with Different Maturity

AhFAD2 is a key enzyme catalyzing the conversion of oleic acid into linoleic acid. The high oleic acid characteristic of peanut mainly comes from the homozygous recessive mutation of AhFAD2A and AhFAD2B genes (aabb). However, even in high-oleic-acid varieties with the aabb genotype, the oleic acid content of seeds with different maturity varies significantly. Therefore, in addition to AhFAD2A and AhFAD2B, other FAD2 members or regulators may be involved in this process. Which FAD2 genes are involved in the regulatory processes associated with seed maturity is still unclear. In this study, four stable lines with different genotypes (AABB, aaBB, AAbb, and aabb) were used to analyze the contents of oleic acid and linoleic acid at different stages of seed development in peanut. Three new AhFAD2 genes (AhFAD2-7, AhFAD2-8, and AhFAD2-9) were cloned based on the whole-genome sequencing results of cultivated peanuts. All peanut FAD2 genes showed tissue preference in expression; however, only the expression level of AhFAD2-7 was positively correlated with the linoleic acid concentration in peanut seeds. These findings provide new insights into the regulation of oleic acid accumulation by maturity, and AhFAD2-7 plays an important role in the maturity dependent accumulation of oleic acid and linoleic acid in peanut.

Heat stress elicits remodeling in the anther lipidome of peanut

Understanding the changes in peanut (Arachis hypogaea L.) anther lipidome under heat stress (HT) will aid in understanding the mechanisms of heat tolerance. We profiled the anther lipidome of seven genotypes exposed to ambient temperature (AT) or HT during flowering. Under AT and HT, the lipidome was dominated by phosphatidylcholine (PC), phosphatidylethanolamine (PE), and triacylglycerol (TAG) species (> 50% of total lipids). Of 89 lipid analytes specified by total acyl carbons:total carbon–carbon double bonds, 36:6, 36:5, and 34:3 PC and 34:3 PE (all contain 18:3 fatty acid and decreased under HT) were the most important lipids that differentiated HT from AT. Heat stress caused decreases in unsaturation indices of membrane lipids, primarily due to decreases in highly-unsaturated lipid species that contained 18:3 fatty acids. In parallel, the expression of Fatty Acid Desaturase 3-2 (FAD3-2; converts 18:2 fatty acids to 18:3) decreased under HT for the heat-tolerant genotype SPT 06-07 but not for the susceptible genotype Bailey. Our results suggested that decreasing lipid unsaturation levels by lowering 18:3 fatty-acid amount through reducing FAD3 expression is likely an acclimation mechanism to heat stress in peanut. Thus, genotypes that are more efficient in doing so will be relatively more tolerant to HT.

Transformation and Characterization of Δ12-Fatty Acid Acetylenase and Δ12-Oleate Desaturase Potentially Involved in the Polyacetylene Biosynthetic Pathway from Bidens pilosa

Bidens pilosa is commonly used as an herbal tea component or traditional medicine for treating several diseases, including diabetes. Polyacetylenes have two or more carbon–carbon triple bonds or alkynyl functional groups and are mainly derived from fatty acid and polyketide precursors. Here, we report the cloning of full-length cDNAs that encode Δ12-fatty acid acetylenase (designated BPFAA) and Δ12-oleate desaturase (designated BPOD) from B. pilosa, which we predicted to play a role in the polyacetylene biosynthetic pathway. Subsequently, expression vectors carrying BPFAA or BPOD were constructed and transformed into B. pilosa via the Agrobacterium-mediated method. Genomic PCR analysis confirmed the presence of transgenes and selection marker genes in the obtained transgenic lines. The copy numbers of transgenes in transgenic lines were determined by Southern blot analysis. Furthermore, 4–5 FAA genes and 2–3 OD genes were detected in wild-type (WT) plants. Quantitative real time-PCR revealed that some transgenic lines had higher expression levels than WT. Western blot analysis revealed OD protein expression in the selected transformants. High-performance liquid chromatography profiling was used to analyze the seven index polyacetylenic compounds, and fluctuation patterns were found.

Integrated Analysis of Comparative Lipidomics and Proteomics Reveals the Dynamic Changes of Lipid Molecular Species in High-Oleic Acid Peanut Seed

Modern peanut contains fatty acid desaturase 2 (FAD2) mutation, which is capable of producing high oleic acid for human health. However, the dynamic changes of the lipidome regarding fad2 remain elusive in peanut seed. In the present study, 547 lipid features were identified in high- and normal-oleic peanut seeds by utilizing the mass spectrometric approach. The fad2-induced differently expressed lipids (DELs) were polarly distributed at early and maturation stages during high-oleic acid (OA) seed development. Subsequently, integration of previously published proteomic data and lipidomic data revealed that 21 proteins and 149 DELs were annotated into the triacylglycerol assembly map, of which nine enzymes and 31 lipid species shared similar variation tendencies. Additionally, the variation tendencies of 17 acyl fatty acids were described in a hypothetical biosynthetic pathway. Collectively, the understanding of the lipid composition correlated with fad2 established a foundation for future high-OA peanut breeding based on lipidomic data.

Cloning and functional analysis of the FAD2 gene family from desert shrub Artemisia sphaerocephala

BACKGROUND

Linoleic acid is an important polyunsaturated fatty acid, required for all eukaryotes. Microsomal delta-12 (Δ12) oleate desaturase (FAD2) is a key enzyme for linoleic acid biosynthesis. Desert shrub Artemisia sphaerocephala is rich in linoleic acid, it has a large FAD2 gene family with twenty-six members. The aim of this work is to unveil the difference and potentially functionality of AsFAD2 family members.

RESULTS

Full-length cDNAs of twenty-one AsFAD2 genes were obtained from A. sphaerocephala. The putative polypeptides encoded by AsFAD2 family genes showed a high level of sequence similarity and were relatively conserved during evolution. The motif composition was also relatively conservative. Quantitative real-time PCR analysis revealed that the AsFAD2-1 gene was strongly expressed in developing seeds, which may be closely associated with the high accumulating ability of linoleic acid in A. sphaerocephala seeds. Although different AsFAD2 family members showed diverse response to salt stress, the overall mRNA levels of the AsFAD2 family genes was stable. Transient expression of AsFAD2 genes in the Nicotiana benthamiana leaves revealed that the encoded proteins were all located in the endoplasmic reticulum. Heterologous expression in Saccharomyces cerevisiae suggested that only three AsFAD2 enzymes, AsFAD2-1, - 10, and - 23, were Δ12 oleate desaturases, which could convert oleic acid to linoleic acid, whereas AsFAD2-1 and AsFAD2-10 could also produce palmitolinoleic acid.

CONCLUSIONS

This research reported the cloning, expression studies, subcellular localization and functional identification of the large AsFAD2 gene family. These results should be helpful in understanding fatty acid biosynthesis in A. sphaerocephala, and has the potential to be applied in the study of plant fatty acids traits.

Genome-Wide Analysis of the Growth-Regulating Factor Family in Peanut (Arachis hypogaea L.)

Growth-regulating factors (GRFs) are plant-specific transcription factors that perform important functions in plant growth and development. Herein, we identified and characterised 24 AhGRF genes in peanut (Arachis hypogaea). AhGRF family genes were divided into six classes with OLQ and WRC domains. Transcriptome expression profile showed that more AhGRF genes, such as AhGRF5a gene, were at higher expression during pod development in Arachis monticola than cultivated species, especially at the pod rapid-expansion stage. AhGRF5a and AhGRF5b genes expressed at higher levels in pods than roots, leaves and stems tissues, existing in the difference between Arachis monticola and H8107. Exogenous GA3 application can activate AhGRF5a and AhGRF5b genes and H8107 line showed more positive response than Arachis monticola species. These results imply that these two AhGRF genes may be active during the peanut pod development.

Transcriptomic Analysis Reveals the High-Oleic Acid Feedback Regulating the Homologous Gene Expression of Stearoyl-ACP Desaturase 2 (SAD2) in Peanuts

Peanuts with high oleic acid content are usually considered to be beneficial for human health and edible oil storage. In breeding practice, peanut lines with high monounsaturated fatty acids are selected using fatty acid desaturase 2 (FAD2), which is responsible for the conversion of oleic acid (C18:1) to linoleic acid (C18:2). Here, comparative transcriptomics were used to analyze the global gene expression profile of high- and normal-oleic peanut cultivars at six time points during seed development. First, the mutant type of FAD2 was determined in the high-oleic peanut (H176). The result suggested that early translation termination occurred simultaneously in the coding sequence of FAD2-A and FAD2-B, and the cultivar H176 is capable of utilizing a potential germplasm resource for future high-oleic peanut breeding. Furthermore, transcriptomic analysis identified 74 differentially expressed genes (DEGs) involved in lipid metabolism in high-oleic peanut seed, of which five DEGs encoded the fatty acid desaturase. Aradu.XM2MR belonged to the homologous gene of stearoyl-ACP (acyl carrier protein) desaturase 2 (SAD2) that converted the C18:0 into C18:1. Further subcellular localization studies indicated that FAD2 was located at the endoplasmic reticulum (ER), and Aradu.XM2MR was targeted to the plastid in Arabidopsis protoplast cells. To examine the dynamic mechanism of this finding, we focused on the peroxidase (POD)-mediated fatty acid (FA) degradation pathway. The fad2 mutant significantly increased the POD activity and H₂O₂ concentration at the early stage of seed development, implying that redox signaling likely acted as a messenger to connect the signaling transduction between the high-oleic content and Aradu.XM2MR transcription level. Taken together, transcriptome analysis revealed the feedback mechanism of SAD2 (Aradu.XM2MR) associated with FAD2 mutation during the seed developmental stage, which could provide a potential peanut breeding strategy based on identified candidate genes to improve the content of oleic acid.

Development of high oleic peanut lines through marker-assisted introgression of mutant ahFAD2 alleles and its fatty acid profiles under open-field and controlled conditions

Peanut is one of the most important oilseed crops grown worldwide. In this study, the mutant ahFAD2 alleles conferring high oleic (HO) content are introgressed into an elite Indian cultivar GPBD4 which is also resistant to the foliar fungal diseases like rust and late leaf spot (LLS). The allele-specific PCR (AS-PCR) and cleaved amplified polymorphic sequences (CAPS) assays were used for the marker-assisted backcross (MABC) approach and 64 HO introgression lines (ILs) were generated. These ILs were tested for the FA compositions under the glasshouse and field conditions. The oleic acid and linoleic acid contents in the ILs were recorded to be between 68.94-82.33% and 1.74-10.87%, respectively, under glasshouse and 67.04-81.71% and 2.00-15.66%, respectively, under field conditions. The increase in the oleic acid content of the ILs over its recurrent parent (RP) was recorded to the tune of 28.78-53.80% and 33.70-62.96% under glasshouse and field conditions, respectively, indicating the stable expression of ahFAD2B gene in two different environments. On the contrary, linoleic acid showed 56.47-93.03% and 40.02-92.34% reduction in the ILs over its RP under glasshouse and field conditions, respectively. These ILs with a healthy FA profile can meet not only the nutritional requirements of a health-conscious society but also the industrial demands for better shelf life of oil and its products.

Association Genetics Identifies Single Nucleotide Polymorphisms Related to Kernel Oil Content and Quality in Camellia oleifera

Camellia oleifera, as an important nonwood tree species for seed oil in China, has received enormous attention owing to its high unsaturated fatty acid contents benefited to human health. It is necessary to examine allelic diversity of key genes that are associated with oil production in C. oleifera cultivars with a large variation of fatty acid compositions. In this study, we performed the association analysis between four key genes (two CoSAD and two Cofad2) coding fatty acid desaturases and traits including oil content and fatty acid composition. We identified two single nucleotide insertion-deletion (InDel) and 362 single-nucleotide polymorphisms (SNPs) within the four candidate genes by sequencing an association population (216 accessions). Single-marker (or haplotype) and traits association tests were conducted by linkage disequilibrium (LD) approaches to detect significant marker-trait associations. Validation population (279 hybrid individuals from six full-sibs families) studies were performed to validate the function of allelic variations significantly associated. In all, 90 single marker-trait and one haplotype-trait associations were significant in association population, and these loci explained 1.87-17.93% proportion of the corresponding phenotypic variance. Further, six SNP marker-trait associations ( Q < 0.10) from Cofad2-A, CoSAD1, and CoSAD2 were successfully validated in the validation population. The SNP markers identified in this study can potentially be applied for future marker-assisted selection to improve oil content and quality in C. oleifera.

CRISPR-Cas9 mediated targeted disruption of FAD2-2 microsomal omega-6 desaturase in soybean (Glycine max.L)

BACKGROUND

Recent innovation in the field of genome engineering encompasses numerous levels of plant genome engineering which attract the substantial excitement of plant biologist worldwide. RNA-guided CRISPR Cas9 system has appeared a promising tool in site-directed mutagenesis due to its innovative utilization in different branches of biology. CRISPR-Cas9 nuclease system have supersedes all previously existed strategies and their associated pitfalls encountered with site-specific mutagenesis.

RESULTS

Here we demonstrated an efficient sequence specific integration/mutation of FAD2-2 gene in soybean using CRISPR-Cas9 nuclease system. A single guided RNA sequence was designed with the help of a number of bioinformatics tools aimed to target distinct sites of FAD2-2 loci in soybean. The binary vector (pCas9-AtU6-sgRNA) has been successfully transformed into soybean cotyledon using Agrobacterium tumafacien. Taken together our findings complies soybean transgenic mutants subjected to targeted mutation were surprisingly detected in our target gene. Furthermore, the detection of Cas9 gene, BAR gene, and NOS terminator were carried out respectively. Southern blot analysis confirmed the stable transformation of Cas9 gene into soybean. Real time expression with qRT-PCR and Sanger sequencing analysis confirmed the efficient CRISPR-Cas9/sgRNA induced mutation within the target sequence of FAD2-2 loci. The integration of FAD2-2 target region in the form of substitution, deletions and insertions were achieved with notably high frequency and rare off-target mutagenesis.

CONCLUSION

High frequent mutation efficiency was recorded as 21% out of all transgenic soybean plants subjected to targeted mutagenesis. Furthermore, Near-infrared spectroscopy (NIR) indicates the entire fatty acid profiling obtained from the mutants seeds of soybean. A considerable modulation in oleic acid content up to (65.58%) whereas the least level of linoleic acid is (16.08%) were recorded. Based on these finding CRISPR-Cas9 system can possibly sum up recent development and future challenges in producing agronomically important crops.

Research Progress in Membrane Lipid Metabolism and Molecular Mechanism in Peanut Cold Tolerance

Early sowing has been extensively used in high-latitude areas to avoid drought stress during sowing; however, cold damage has become the key limiting factor of early sowing. To relieve cold stress, plants develop a series of physiological and biochemical changes and sophisticated molecular regulatory mechanisms. The biomembrane is the barrier that protects cells from injury as well as the primary place for sensing cold signals. Chilling tolerance is closely related to the composition, structure, and metabolic process of membrane lipids. This review focuses on membrane lipid metabolism and its molecular mechanism, as well as lipid signal transduction in peanut (Arachis hypogaea L.) under cold stress to build a foundation for explicating lipid metabolism regulation patterns and physiological and molecular response mechanisms during cold stress and to promote the genetic improvement of peanut cold tolerance.

TALEN-mediated targeted mutagenesis of fatty acid desaturase 2 (FAD2) in peanut (Arachis hypogaea L.) promotes the accumulation of oleic acid

A first creation of high oleic acid peanut varieties by using transcription activator-like effecter nucleases (TALENs) mediated targeted mutagenesis of Fatty Acid Desaturase 2 (FAD2). Transcription activator like effector nucleases (TALENs), which allow the precise editing of DNA, have already been developed and applied for genome engineering in diverse organisms. However, they are scarcely used in higher plant study and crop improvement, especially in allopolyploid plants. In the present study, we aimed to create targeted mutagenesis by TALENs in peanut. Targeted mutations in the conserved coding sequence of Arachis hypogaea fatty acid desaturase 2 (AhFAD2) were created by TALENs. Genetic stability of AhFAD2 mutations was identified by DNA sequencing in up to 9.52 and 4.11% of the regeneration plants at two different targeted sites, respectively. Mutation frequencies among AhFAD2 mutant lines were significantly correlated to oleic acid accumulation. Genetically, stable individuals of positive mutant lines displayed a 0.5-2 fold increase in the oleic acid content compared with non-transgenic controls. This finding suggested that TALEN-mediated targeted mutagenesis could increase the oleic acid content in edible peanut oil. Furthermore, this was the first report on peanut genome editing event, and the obtained high oleic mutants could serve for peanut breeding project.

Seed Transcriptomics Analysis in Camellia oleifera Uncovers Genes Associated with Oil Content and Fatty Acid Composition

Camellia oleifera is a major tree species for producing edible oil. Its seed oil is well known for the high level of oleic acids; however, little is known regarding the molecular mechanism of lipid biosynthesis in C. oleifera. Here, we measured the oil contents and fatty acid (FA) compositions at four developmental stages and investigated the global gene expression profiles through transcriptomics sequencing. We identified differentially-expressed genes (DEGs) among the developmental stages and found that the distribution of numbers of DEGs was associated with the accumulation pattern of seed oil. Gene Ontology (GO) enrichment analysis revealed some critical biological processes related to oil accumulation, including lipid metabolism and phosphatidylcholine metabolism. Furthermore, we investigated the expression patterns of lipid biosynthesis genes. We showed that most of the genes were identified with single or multiple copies, and some had correlated profiles along oil accumulation. We proposed that the higher levels of stearoyl-ACP desaturases (SADs) coupled with lower activities of fatty acid desaturase 2 (FAD2) might be responsive to the boost of oleic acid at the late stage of C. oleifera seeds’ development. This work presents a comprehensive transcriptomics study of C. oleifera seeds and uncovers valuable DEGs that are associated with the seed oil accumulation.

Isolation and functional analysis of fatty acid desaturase genes from peanut (Arachis hypogaea L.)

BACKGROUND

Fatty acid desaturases are enzymes that introduce double bonds into fatty acyl chains. Extensive studies of fatty acid desaturases have been done in many plants. However, less is known about the diversity of this gene family in peanut (Arachis hypogaea L.), an important oilseed crop that is cultivated worldwide.

RESULTS

In this study, twelve novel AhFADs genes were identified and isolated from peanut. Quantitative real-time PCR analysis indicated that the transcript abundances of AhFAB2-2 and AhFAD3-1 were higher in seeds than in other tissues examined, whereas the AhADS and AhFAD7-1 transcripts were more abundant in leaves. AhFAB2-3, AhFAD3-2, AhFAD4, AhSLD-4, and AhDES genes were highly expressed in flowers, whereas AhFAD7-2, AhSLD-2, and AhSLD-3 were expressed most strongly in stems. During seed development, the expressions of AhFAB2-2, AhFAD3-1, AhFAD7-1, and AhSLD-3 gradually increased in abundance, reached a maximum expression level, and then decreased. The AhFAB2-3, AhFAD3-2, AhFAD4, AhADS, and AhDES transcript levels remained relatively high at the initial stage of seed development, but decreased thereafter. The AhSLD-4 transcript level remained relatively low at the initial stage of seed development, but showed a dramatic increase in abundance at the final stage. The AhFAD7-2 and AhSLD-2 transcript levels remained relatively high at the initial stage of seed development, but then decreased, and finally increased again. The AhFAD transcripts were differentially expressed following exposure to abiotic stresses or abscisic acid. Moreover, the functions of one AhFAD6 and four AhSLD genes were confirmed by heterologous expression in Synechococcus elongates or Saccharomyces cerevisiae.

CONCLUSIONS

The present study provides valuable information that improves understanding of the biological roles of FAD genes in fatty acid synthesis, and will help peanut breeders improve the quality of peanut oil via molecular design breeding.

The FAD2 Gene in Plants: Occurrence, Regulation, and Role

Vegetable oils rich in oleic acid are more desirable than oils rich in polyunsaturated and saturated fatty acids. The biological switch of oleic acid to linoleic acid is facilitated by fatty acid desaturase 2 enzyme that is further classified into FAD2-1, FAD2-2, FAD2-3, and FAD2-4. The genes coding these enzymes have high sequence similarity, but differ mostly in their expression patterns. The seed-type FAD2 genes had evolved independently after segregation by duplication from constitutively expressed FAD2 genes. Temperature, light and wounding effectively regulate FAD2 expression in plants. FAD2 genes are expressed differently in different tissues of the plant, and the over-expression of FAD2 modifies physiological and vegetative characteristics. The activity of FAD2 leads to an increase in the content of dienoic fatty acids, and hence increases the resistance toward cold and salt stress. The thorough study of the FAD2 gene is important for understanding the expression, regulation and mechanism that will help in improving the quality of oil and stress resistance in plants.

Mapping of important taxonomic and productivity traits using genic and non-genic transposable element markers in peanut (Arachis hypogaea L.)

A mapping population of recombinant inbred lines (RILs) derived from TMV 2 and its mutant, TMV 2-NLM was employed for mapping important taxonomic and productivity traits using genic and non-genic transposable element markers in peanut. Single nucleotide polymorphism and copy number variation using RAD-Sequencing data indicated very limited polymorphism between TMV 2 and TMV 2-NLM. But phenotypically they differed significantly for many taxonomic and productivity traits. Also, the RIL population showed significant variation for a few additional agronomic traits. A genetic linkage map of 1,205.66 cM was constructed using 91 genic and non-genic Arachis hypogaea transposable element (AhTE) markers. Using single marker analysis and QTL analysis, the markers with high phenotypic variance explained (PVE) were identified for branching pattern (32.3%), number of primary and secondary branches (19.9% and 28.4%, respectively), protein content (26.4%), days to 50% flowering (22.0%), content of oleic acid (15.1%), test weight (13.6%) and pod width (12.0%). Three genic markers (AhTE0357, AhTE0391, AhTE0025) with Arachis hypogaea miniature inverted-repeat transposable element (AhMITE1) activity in the genes Araip.TG1BL (B02 chromosome), Aradu.7N61X (A09 chromosome) and Aradu.7065G (A07 chromosome), respectively showed strong linkage with these taxonomic, productivity and quality traits. Since TMV 2 and TMV 2-NLM differed subtly at DNA level, the background noise in detecting the marker-trait associations was minimum; therefore, the markers identified in this study for the taxonomic and productivity traits may be significant and useful in peanut molecular breeding.

Insights into the Indian Peanut Genotypes for ahFAD2 Gene Polymorphism Regulating Its Oleic and Linoleic Acid Fluxes

In peanut (Arachis hypogaea L.), the customization of fatty acid profile is an evolving area to fulfill the nutritional needs in the modern market. A total of 174 peanut genotypes, including 167 Indian cultivars, 6 advanced breeding lines and "SunOleic95R"-a double mutant line, were investigated using AS-PCRs, CAPS and gene sequencing for the ahFAD2 allele polymorphism, along with its fatty acid compositions. Of these, 80 genotypes were found having substitution (448G>A) mutation only in ahFAD2A gene, while none recorded 1-bp insertion (441_442insA) mutation in ahFAD2B gene. Moreover, 22 wild peanut accessions found lacking both the mutations. Among botanical types, the ahFAD2A mutation was more frequent in ssp. hypogaea (89%) than in ssp. fastigiata (17%). This single allele mutation, found affecting not only oleic to linoleic acid fluxes, but also the composition of other fatty acids in the genotypes studied. Repeated use of a few selected genotypes in the Indian varietal development programs were also eminently reflected in its ahFAD2 allele polymorphism. Absence of known mutations in the wild-relatives indicated the possible origin of these mutations, after the allotetraploidization of cultivated peanut. The SNP analysis of both ahFAD2A and ahFAD2B genes, revealed haplotype diversity of 1.05% and 0.95%, while Ka/Ks ratio of 0.36 and 0.39, respectively, indicating strong purifying selection pressure on these genes. Cluster analysis, using ahFAD2 gene SNPs, showed presence of both mutant and non-mutant genotypes in the same cluster, which might be due the presence of ahFAD2 gene families. This investigation provided insights into the large number of Indian peanut genotypes, covering various aspects related to O/L flux regulation and ahFAD2 gene polymorphism.