Morpho-Agronomic and Biochemical Characterization of Accessions of Tiger Nut (Cyperus esculentus) Grown in the North Temperate Zone of China

Insights into membrane-bound fatty acid desaturase genes in tigernut (Cyperus esculentus L.), an oil-rich tuber plant in Cyperaceae

BACKGROUND

Tigernut (Cyperus esculentus L.), an oil-rich tuber plant of the Cyperaceae family, is typical for the naturally high content of oleic acid. However, to date, genes contributing to oil composition have not been well characterized.

RESULTS

In this study, the first genome-wide analysis of tigernut genes encoding membrane-bound fatty acid desaturases (FADs), the key contributors to oil composition, is presented. According to phylogenetic analysis, ten members identified from the tigernut genome were assigned into seven out of eight evolutionary groups as defined in Arabidopsis thaliana, i.e., FAD2 (3), FAD6 (1), FAD3 (1), FAD7 (1), FAD4 (1), DES (1), and SLD (2). In contrast to the absence of an FAD5 homolog, FAD2 and SLD in tigernut were shown to have expanded via tandem and dispersed duplications, respectively. Comparison of 285 members from 29 representative plant species resulted in 11 orthogroups, where FAD2a, FAD6, FAD7, FAD3, FAD4, FAD5, DES, and SLD1 were shown to have already appeared in the ancestor of seed plants. Significantly, orthologous and syntenic analyses revealed that loss of FAD5 and expansion of SLD in tigernut are lineage-specific, occurred sometime before the radiation of core monocots, in contrast to species-specific expansion of FAD2. Moreover, though no syntenic relationship was observed between CeFAD genes, our comparative genomics analyses indicated that FAD3 and -7 are more likely to arise from segmental duplication. Structural variation and expression divergence of CeFAD genes were also observed. Gain of introns in CeFAD4, CeSLD1, and CeSLD2 was shown to be lineage-specific, occurred sometime before Cyperaceae-Juncaceae split. Tissue-specific expression analysis revealed that CeFAD2-1, CeFAD6, and CeFAD7 were constitutively expressed, whereas others were tissue-specific. Among five paralogs identified, CeFAD2-1 and CeSLD1 have evolved to be two dominant members. Putative roles of CeFAD2-1 in oil accumulation are supported by 1) exhibited an expression pattern positively associated with oil accumulation during tuber development; 2) were expressed more in tubers than their orthologs in C. rotundus. Additionally, in contrast to high expression of CrFAD3, transcript levels of CeFAD3 in tubers were fairly low, which may explain the distinct α-linolenic acid content between these two close species.

CONCLUSIONS

Our findings provide a global view of CeFAD genes, which not only highlights lineage-specific evolution of the family, but also provides valuable information for further functional analysis and genetic improvement in tigernut.

Integrative Analysis Provides Insights into Genes Encoding LEA_5 Domain-Containing Proteins in Tigernut (Cyperus esculentus L.)

LEA_5 domain-containing proteins constitute a small family of late embryogenesis-abundant proteins that are essential for seed desiccation tolerance and dormancy. However, their roles in non-seed storage organs such as underground tubers are largely unknown. This study presents the first genome-scale analysis of the LEA_5 family in tigernut (Cyperus esculentus L.), a Cyperaceae plant producing desiccation-tolerant tubers. Four LEA_5 genes identified from the tigernut genome are twice of two present in model plants Arabidopsis thaliana and Oryza sativa. A comparison of 86 members from 34 representative plant species revealed the monogenic origin and lineage-specific family evolution in Poales, which includes the Cyperaceae family. CeLEA5 genes belong to four out of five orthogroups identified in this study, i.e., LEA5a, LEA5b, LEA5c, and LEA5d. Whereas LEA5e is specific to eudicots, LEA5b and LEA5d appear to be Poales-specific and LEA5c is confined to families Cyperaceae and Juncaceae. Though no syntenic relationship was observed between CeLEA5 genes, comparative genomics analyses indicated that LEA5b and LEA5c are more likely to arise from LEA5a via whole-genome duplication. Additionally, local duplication, especially tandem duplication, also played a role in the family expansion in Juncus effuses, Joinvillea ascendens, and most Poaceae plants examined in this study. Structural variation (e.g., fragment insertion) and expression divergence of LEA_5 genes were also observed. Whereas LEA_5 genes in A. thaliana, O. sativa, and Zea mays were shown to be preferentially expressed in seeds/embryos, CeLEA5 genes have evolved to be predominantly expressed in tubers, exhibiting seed desiccation-like accumulation during tuber maturation. Moreover, CeLEA5 orthologs in C. rotundus showed weak expression in various stages of tuber development, which may explain the difference in tuber desiccation tolerance between these two close species. These findings highlight the lineage-specific evolution of the LEA_5 family, which facilitates further functional analysis and genetic improvement in tigernut and other species.

Insights into the Stearoyl-Acyl Carrier Protein Desaturase (SAD) Family in Tigernut (Cyperus esculentus L.), an Oil-Bearing Tuber Plant

Plant oils rich in oleic acid (OA) are attracting considerable attention for their high nutritional value and significant industrial potential. Stearoyl-acyl carrier protein desaturases (SADs) are a class of soluble desaturases that play a key role in OA accumulation in plants. In this study, the first genome-wide characterization of the SAD gene family was conducted in tigernut (Cyperus esculentus L. var. sativus Baeck., Cyperaceae), an oil-rich tuber plant typical for its high OA content. Six SAD genes identified from the tigernut genome are comparative to seven reported in two model plants Arabidopsis thaliana and Oryza sativa, but relatively more than four were found in most Cyperaceae species examined in this study. A comparison of 161 SAD genes from 29 representative plant species reveals the monogenic origin and lineage-specific family evolution in Poales. C. esculentus SAD genes (CeSADs) were shown to constitute two evolutionary groups (i.e., FAB2 and AAD) and four out of 12 orthogroups identified in this study, i.e., FAB2a, FAB2b, FAB2c, and AAD1. Whereas FAB2a and AAD1 are widely distributed, FAB2b and FAB2c are specific to Cyperaceae, which may arise from FAB2a via tandem and dispersed duplications, respectively. Though FAB2d and AAD2 are also broadly present in monocots, they are more likely to be lost in the Cyperaceae ancestor sometime after the split with its close family, Juncaceae. In tigernut, FAB2a appears to have undergone species-specific expansion via tandem duplication. Frequent structural variation and apparent expression divergence were also observed. Though FAB2a and AAD1 usually feature two and one intron, respectively, gain of certain introns was observed in CeSAD genes, all of which have three introns. Despite recent expansion of the FAB2 group, CeFAB2-1 has evolved into the dominant member that was highly and constitutively expressed in all tested organs. Moreover, CeFAB2-1, CeAAD1, as well as CeFAB2-5 have evolved to be predominantly expressed in tubers and thus contribute to high OA accumulation. These findings highlight lineage-specific evolution of the SAD family and putative roles of CeSAD genes in tuber oil accumulation, which facilitate further functional analysis and genetic improvement in tigernut and other species.

Yield, physicochemical properties and in vitro digestibility of starch isolated from defatted meal made from microwaved tigernut (Cyperus esculentus L.) tubers

In this work, the effects of microwave treatment (MDT) of tigernut tubers at 540 W for 140, 180, 220, 240 s on the yield, physicochemical properties and in vitro digestibility of tigernut starch (TS) were firstly investigated. MDT significantly reduced the crystallinity and double helix structures of the starch, without altering its native A-type crystal structure. After microwaving for 140 s and 180 s, the extraction yield of TS was significantly increased from 14.92 % to 16.68 %, and a dense gel network structure was found by rheological analysis. In vitro digestion results indicated that the microwaved TS contained more content of rapidly digestible starch (RDS, 76.10 %-80.74 %) but lower slowly digestible starch (SDS, 2.85 %-5.78 %) and resistant starch (RS, 14.94 %-18.12 %); in other words, microwaving increased the in vitro digestibility of TS. This work elucidated the essential features of the response of tigernut starch to microwave treatment, and provided a basic understand of the digestibility of tigernut starch under microwave treatment, making it more suitable for industrial applications.

A review on the biological and bioactive components of Cyperus esculentus L.: insight on food, health and nutrition

Tiger nut (Cyperus esculentus L.) is a small, tuberous root vegetable that has gained increasing attention in recent years due to its potential health benefits. This review article provides an elaborate overview of tiger nut, including its botany, historical uses, nutritional composition, potential health benefits and traditional medicinal uses. This review article comprehensively discusses the nutritional profile of tiger nut, providing a detailed understanding of its nutrient content. Furthermore, the potential health benefits of tiger nut are thoroughly reviewed, including its effects on digestive health, cardiovascular health, blood sugar control, immune function and other potential therapeutic uses. Scientific articles used for this review were retrieved from ScienceDirect, Google Scholar, PubMed and SciELO databases. Only articles published between 1997 and 2022 were used for research. This review contributes to a better understanding of tiger nut and its prospective uses in functional foods and medicine by combining the available scientific material. © 2024 Society of Chemical Industry.

The changed structures of Cyperus esculentus protein decide its modified physicochemical characters: Effects of ball-milling, high pressure homogenization and cold plasma treatments on structural and functional properties of the protein

Three physical treatments, including ball-milling (BM), high pressure homogenization (HPH) and cold plasma (CP) were applied to modify structural and functional properties of Cyperus esculentus protein (CEP). The results showed that three treatments significantly altered morphology and reduced particle size of CEP. Both primary and secondary structures of CEP were hardly changed, while disulfide bonds and hydrophobic forces between amino acid residues of CEP were interrupted by three treatments, releasing free sulfhydryls and hydrophobic groups. With the free moiety accumulation, the reformed interactions between them enhanced the crystallinity and thermostability of CEP. Besides, solubility and emulsifying properties of CEP were significantly improved within a certain range of treatment duration and intensity, and three treatments decreased water but increased oil holding capacity of CEP. Conclusively, the modified physicochemical properties of CEP were decided by the changed molecular structures of CEP, and different treatments may satisfy different processing requirements for the protein.

Analysis of Lhc family genes reveals development regulation and diurnal fluctuation expression patterns in Cyperus esculentus, a Cyperaceae plant

Sixteen Lhc genes representing 13 phylogenetic groups were identified from the full-length transcriptome of tigernut, exhibiting development regulation and diurnal fluctuation expression patterns in leaves. Nuclear encoded light-harvesting chlorophyll a/b-binding (Lhc) proteins play indispensable roles in oxygenic photosynthesis. In this study, we present the first transcriptome-based characterization of Lhc family genes in tigernut (Cyperus esculentus L.), a Cyperaceae C₄ plant producing oil in underground tubers. A number of 16 Lhc genes representing 13 phylogenetic groups identified from the full-length tigernut transcriptome are equal to that found in both Carex littledalei (another Cyperaceae plant) and papaya, slightly more than 15 members present in both rice and jatropha, but relatively less than 18, 20, and 21 members present in sorghum, cassava, and Arabidopsis, respectively. Nevertheless, nearly one-vs-one orthologous relationship was observed in most groups, though some of them are no longer located in syntenic blocks and species-specific expansion was frequently found in Lhcb1. Comparative genomics analysis revealed that the loss of two groups (i.e., Lhca2 and Lhca5) in C. littledalei is species-specific, sometime after the split with tigernut, and the expansion of Lhcb1 was mainly contributed by tandem duplication as observed in most species. Interestingly, a transposed duplication, which appears to be shared by monocots, was also identified in Lhcb1. Further transcriptome profiling revealed a predominant expression pattern of most CeLhc family genes in photosynthetic tissues and enhanced transcription during leaf maturation, reflecting their key roles in light absorption. Moreover, qRT-PCR analysis revealed an apparent diurnal fluctuation expression pattern of 11 dominant CeLhc genes. These findings not only highlight species-specific evolution of Lhc genes in the Cyperaceae family as well as the monocot lineage, but also provide valuable information for further functional analysis and genetic improvement in tigernut.

RNA-Seq Analysis Demonstrates Different Strategies Employed by Tiger Nuts (Cyperus esculentus L.) in Response to Drought Stress

Drought stress, an important abiotic stress, has affected global agricultural production by limiting the yield and the quality of crops. Tiger nuts (Cyperus esculentus L.) are C4 crops in the Cyperaceae family, which have high-quality wholesome ingredients. However, data on mechanisms underlying the response of tiger nuts to drought stress are few. Here, the variety of Jisha 1 and 15% polyethylene glycol (PEG; a drought stress simulator) were used to study the mechanisms of stress response in tiger nuts. Our evaluation of the changes in physiological indicators such as electrolyte leakage (El), malondialdehyde (MDA), hydrogen peroxide (H₂O₂), superoxide anion (O₂⁻) and activities of reactive oxygen species (ROS) showed that 12 h was the most suitable time point to harvest and analyze the response to drought stress. Thereafter, we performed transcriptome (RNA-Seq) analysis in the control (CK) and stress treatment groups and showed that there was a total of 1760 differentially expressed genes (DEGs). Gene Ontology (GO) analysis showed that the DEGs were enriched in abscisic acid (ABA) terms, and pathways such as starch and sucrose metabolism (ko00500), phenylpropanoid biosynthesis (ko00940) and plant hormone signal transduction (ko04075) were significantly enriched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. In addition, quantitative real-time PCR (qRT-PCR) analysis of the DEGs demonstrated an upregulation of ABA and lignin content, as well as enzyme activities in enriched pathways, which validated the RNA-Seq data. These results revealed the pathways and mechanisms adopted by the tiger nuts in response to drought stress.