Critical metabolic pathways and SAD/FADs, WRI1s, and DGATs cooperate for high-oleic acid oil production in developing oil tea (Camellia oleifera) seeds

Characterization of a new Camellia plant resource with low caffeine and high theobromine for production of a novel natural low-caffeine tea

Yuanbaoshancha (YBSC) is characterized as a new wild tea relative morphologically and phytochemically distinguished from the closest wild tea plants Rongjiangcha (Camellia yungkiangensis, RJC) and Tulecha (Camellia costata, TLC). YBSC young leaves contain higher tea polyphenol and theobromine contents but lower caffeine and theanine as compared with RJC, TLC, and other tea landraces and modern cultivars. The major alkaloid detected in YBSC, TLC, and RJC is theobromine while caffeine is a minor; the primary catechins in YBSC leaves are non-galloylated catechins, significantly different from Camellia sinensis and other low-caffeine tea resources. The unique phytochemical profiles featured YBSC black tea with extremely lower caffeine and higher theobromine, as well as unique flavors and health benefits. This botanical characterization of YBSC and two related low-caffeine wild tea resources lays a foundation for future better utilization for the production of a highly valuable natural low-caffeine/high-theobromine tea.

Chemical compounds

Caffeine (PubChem CID: 2519); Theobromine (PubChem CID: 5429); Catechins (PubChem CID: 9064); Epigallocatechin gallate (PubChem CID: 65064); Theanine (PubChem CID: 439378); Jasmone (PubChem CID: 1549018); cis-3-Hexenyl hexanoate (PubChem CID: 5352543); Hexyl 2-methylbutanoate (PubChem CID: 24838).

High-Density Genetic Map Construction and Quantitative Trait Locus Analysis of Fruit- and Oil-Related Traits in Camellia oleifera Based on Double Digest Restriction Site-Associated DNA Sequencing

Camellia oleifera, an important tree species and source of edible oil in China, has received significant attention owing to the oil's high unsaturated fatty acid content, which has benefits for human health. However, the mechanisms underlying C. oleifera yield and oil quality are largely unknown. In this study, 180 F1 progenies were obtained from two parents with obvious differences in fruit- and oil-related traits. We constructed a high-density genetic map using a double digest restriction site-associated DNA sequencing (ddRAD-Seq) strategy in C. oleifera. This map spanned 3327 cM and anchored 2780 markers in 15 linkage groups (LGs), with an average marker interval of 1.20 cM. A total of 221 quantitative trait loci (QTLs) associated with fruit- and oil-related traits were identified across three years' worth of phenotypic data. Nine QTLs were detected simultaneously in at least two different years, located on LG02, LG04, LG05, LG06, and LG11, and explained 8.5-16.6% of the phenotypic variation in the corresponding traits, respectively. Seventeen major QTLs were obtained that explained 13.0-16.6% of the phenotypic variance. Eleven and five flanking SNPs of major QTLs for fruit- and oil-related traits were detected which could be used for marker-assisted selection in C. oleifera breeding programs. Furthermore, 202 potential candidate genes in QTL regions were identified based on the collinearity of the genetic map and the C. oleifera "CON" genome. A potential regulatory network controlling fruit development and oil biosynthesis was constructed to dissect the complex mechanism of oil accumulation. The dissection of these QTLs will facilitate the gene cloning underlying lipid synthesis and increase our understanding in order to enhance C. oleifera oil yield and quality.

Comparative Transcriptomic and Lipidomic Analysis of Fatty Acid Accumulation in Three Camellia oleifera Varieties During Seed Maturing

Camellia oleifera, a major woody oil crop in China, produces tea oil rich in unsaturated fatty acids, earning it names like liquid gold and eastern olive oil. This study provides an integrated investigation of the transcriptome and lipidome within seeds at the maturing process across three C. oleifera varieties, revealing a significant relationship between fatty acid production and genes involved in lipid synthesis. Through transcriptomic analysis, 26,344 genes with varied expression were found. Functional enrichment analysis highlighted that pathways related to starch and sucrose metabolism, plant hormone signal transduction, and lipid accumulation were highly enriched among the differentially expressed genes. Coordinated high expression of key genes (ACCase, KAS I, KAS II, KAS III, KAR, HAD, EAR, SAD, LPAAT, LACS, DGAT, PDAT) during the late maturation stage contributes largely to high oil content. Additionally, expression variations of SAD and FADs among different varieties were explored. The analysis suggests that high expression of genes such as FAD3, FAD7, and FAD8 notably increased linolenic acid content. This research provides new insights into the molecular mechanisms of oil biosynthesis in C. oleifera, offering valuable references for improving yield and quality.

Genome-Wide Analyses of MADS-Box Genes Reveal Their Involvement in Seed Development and Oil Accumulation of Tea-Oil Tree (Camellia oleifera)

The seeds of Camellia oleifera produce high amount of oil, which can be broadly used in the fields of food, industry, and medicine. However, the molecular regulation mechanisms of seed development and oil accumulation in C. oleifera are unclear. In this study, evolutionary and expression analyses of the MADS-box gene family were performed across the C. oleifera genome for the first time. A total of 86 MADS-box genes (ColMADS) were identified, including 60 M-type and 26 MIKC members. More gene duplication events occurred in M-type subfamily (6) than that in MIKC subfamily (2), and SEP-like genes were lost from the MIKCC clade. Furthermore, 8, 15, and 17 differentially expressed ColMADS genes (DEGs) were detected between three developmental stages of seed (S1/S2, S2/S3, and S1/S3), respectively. Among these DEGs, the STK-like ColMADS12 and TT16-like ColMADS17 were highly expressed during the seed formation (S1 and S2), agreeing with their predicted functions to positively regulate the seed organogenesis and oil accumulation. While ColMADS57 and ColMADS07 showed increasing expression level with the seed maturation (S2 and S3), conforming to their potential roles in promoting the seed ripening. In all, these results revealed a critical role of MADS-box genes in the C. oleifera seed development and oil accumulation, which will contribute to the future molecular breeding of C. oleifera.

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

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

Key FAD2, FAD3, and SAD Genes Involved in the Fatty Acid Synthesis in Flax Identified Based on Genomic and Transcriptomic Data

FAD (fatty acid desaturase) and SAD (stearoyl-ACP desaturase) genes play key roles in the synthesis of fatty acids (FA) and determination of oil composition in flax (Linum usitatissimum L.). We searched for FAD and SAD genes in the most widely used flax genome of the variety CDC Bethune and three available long-read assembled flax genomes-YY5, 3896, and Atlant. We identified fifteen FAD2, six FAD3, and four SAD genes. Of all the identified genes, 24 were present in duplicated pairs. In most cases, two genes from a pair differed by a significant number of gene-specific SNPs (single nucleotide polymorphisms) or even InDels (insertions/deletions), except for FAD2a-1 and FAD2a-2, where only seven SNPs distinguished these genes. Errors were detected in the FAD2a-1, FAD2a-2, FAD3c-1, and FAD3d-2 sequences in the CDC Bethune genome assembly but not in the long-read genome assemblies. Expression analysis of the available transcriptomic data for different flax organs/tissues revealed that FAD2a-1, FAD2a-2, FAD3a, FAD3b, SAD3-1, and SAD3-2 were specifically expressed in embryos/seeds/capsules and could play a crucial role in the synthesis of FA in flax seeds. In contrast, FAD2b-1, FAD2b-2, SAD2-1, and SAD2-2 were highly expressed in all analyzed organs/tissues and could be involved in FA synthesis in whole flax plants. FAD2c-2, FAD2d-1, FAD3c-1, FAD3c-2, FAD3d-1, FAD3d-2, SAD3-1, and SAD3-2 showed differential expression under stress conditions-Fusarium oxysporum infection and drought. The obtained results are essential for research on molecular mechanisms of fatty acid synthesis, FAD and SAD editing, and marker-assisted and genomic selection for breeding flax varieties with a determined fatty acid composition of oil.

Analysis of Delta(9) fatty acid desaturase gene family and their role in oleic acid accumulation in Carya cathayensis kernel

Carya cathayensis, commonly referred to as Chinese hickory, produces nuts that contain high-quality edible oils, particularly oleic acid (18:1). It is known that stearoyl-ACP desaturase (SAD) is the first key step converting stearic acid (C18:0, SA) to oleic acid (C18:1, OA) in the aminolevulinic acid (ALA) biosynthetic pathway and play an important role in OA accumulation. Thus far, there is little information about SAD gene family in C. cathayensis and the role of individual members in OA accumulation. This study searched the Chinese Hickory Genome Database and identified five members of SAD genes, designated as CcSADs, at the whole genome level through the comparison with the homologous genes from Arabidopsis. RNA-Seq analysis showed that CcSSI2-1, CcSSI2-2, and CcSAD6 were highly expressed in kernels. The expression pattern of CcSADs was significantly correlated with fatty acid accumulation during the kernel development. In addition, five full-length cDNAs encoding SADs were isolated from the developing kernel of C. cathayensis. CcSADs-green fluorescent protein (GFP) fusion construct was infiltrated into tobacco epidermal cells, and results indicated their chloroplast localization. The catalytic function of these CcSADs was further analyzed by heterologous expression in Saccharomyces cerevisiae, Nicotiana benthamiana, and walnut. Functional analysis demonstrated that all CcSADs had fatty acid desaturase activity to catalyze oleic acid biosynthesis. Some members of CcSADs also have strong substrate specificity for 16:0-ACP to synthesize palmitoleic acid (C16:1, PA). Our study documented SAD gene family in C. cathayensis and the role of CcSSI2-1, CcSSI2-2, and CcSAD6 in OA accumulation, which could be important for future improvement of OA content in this species via genetic manipulation.

Transcriptome and Anatomical Comparisons Reveal the Effects of Methyl Jasmonate on the Seed Development of Camellia oleifera

Seed is a major storage organ that determines the yield and quality of Camellia oleifera (C. oleifera). Methyl jasmonate (MeJA) is a signaling molecule involved in plant growth and development. However, the role of MeJA in the development of C. oleifera seeds remains a mystery. This study demonstrated that the larger seeds induced by MeJA resulted from more cell numbers and a larger cell area in the outer seed coat and embryo at the cellular level. At the molecular level, MeJA could regulate the expression of factors in the known signaling pathways of seed size control as well as cell proliferation and expansion, resulting in larger seeds. Furthermore, the accumulation of oil and unsaturated fatty acids due to MeJA-inducement was attributed to the increased expression of fatty acid biosynthesis-related genes but reduced expression of fatty acid degradation-related genes. CoMYC2, a key regulator in jasmonate signaling, was considered a potential hub regulator which directly interacted with three hub genes (CoCDKB2-3, CoCYCB2-3, and CoXTH9) related to the seed size and two hub genes (CoACC1 and CoFAD2-3) related to oil accumulation and fatty acid biosynthesis by binding to their promoters. These findings provide an excellent target for the improvement of the yield and quality in C. oleifera.

Genome-wide analysis of fatty acid desaturase genes in chia (Salvia hispanica) reveals their crucial roles in cold response and seed oil formation

Chia (Salvia hispanica) is a functional food crop with high α-linolenic acid (ALA), the omega-3 essential fatty acid, but its worldwide plantation is limited by cold-intolerance and strict short-photoperiod flowering feature. Fatty acid desaturases (FADs) are responsible for seed oil accumulation, and play important roles in cold stress tolerance of plants. To date, there is no report on systemically genome-wide analysis of FAD genes in chia (ShiFADs). In this study, 31 ShiFAD genes were identified, 3 of which contained 2 alternative splicing transcripts, and they were located in 6 chromosomes of chia. Phylogenetic analysis classified the ShiFAD proteins into 7 groups, with conserved gene structure and MEME motifs within each group. Tandem and segmental duplications coursed the expansion of ShiFAD genes. Numerous cis-regulatory elements, including hormone response elements, growth and development elements, biotic/abiotic stress response elements, and transcription factor binding sites, were predicted in ShiFAD promoters. 24 miRNAs targeting ShiFAD genes were identified at whole-genome level. In total, 15 SSR loci were predicted in ShiFAD genes/promoters. RNA-seq data showed that ShiFAD genes were expressed in various organs with different levels. qRT-PCR detection revealed the inducibility of ShiSAD2 and ShiSAD7 in response to cold stress, and validated the seed-specific expression of ShiSAD11a. Yeast expression of ShiSAD11a confirmed the catalytic activity of its encoded protein, and its heterologous expression in Arabidopsis thaliana significantly increased seed oleic acid content. This work lays a foundation for molecular dissection of chia high-ALA trait and functional study of ShiFAD genes in cold tolerance.

Maturity Grading and Identification of Camellia oleifera Fruit Based on Unsupervised Image Clustering

Maturity grading and identification of Camellia oleifera are prerequisites to determining proper harvest maturity windows and safeguarding the yield and quality of Camellia oil. One problem in Camellia oleifera production and research is the worldwide confusion regarding the grading and identification of Camellia oleifera fruit maturity. To solve this problem, a Camellia oleifera fruit maturity grading and identification model based on the unsupervised image clustering model DeepCluster has been developed in the current study. The proposed model includes the following two branches: a maturity grading branch and a maturity identification branch. The proposed model jointly learns the parameters of the maturity grading branch and maturity identification branch and used the maturity clustering assigned from the maturity grading branch as pseudo-labels to update the parameters of the maturity identification branch. The maturity grading experiment was conducted using a training set consisting of 160 Camellia oleifera fruit samples and 2628 Camellia oleifera fruit digital images collected using a smartphone. The proposed model for grading Camellia oleifera fruit samples and images in training set into the following three maturity levels: unripe (47 samples and 883 images), ripe (62 samples and 1005 images), and overripe (51 samples and 740 images). Results suggest that there was a significant difference among the maturity stages graded by the proposed method with respect to seed oil content, seed soluble protein content, seed soluble sugar content, seed starch content, dry seed weight, and moisture content. The maturity identification experiment was conducted using a testing set consisting of 160 Camellia oleifera fruit digital images (50 unripe, 60 ripe, and 50 overripe) collected using a smartphone. According to the results, the overall accuracy of maturity identification for Camellia oleifera fruit was 91.25%. Moreover, a Gradient-weighted Class Activation Mapping (Grad-CAM) visualization analysis reveals that the peel regions, crack regions, and seed regions were the critical regions for Camellia oleifera fruit maturity identification. Our results corroborate a maturity grading and identification application of unsupervised image clustering techniques and are supported by additional physical and quality properties of maturity. The current findings may facilitate the harvesting process of Camellia oleifera fruits, which is especially critical for the improvement of Camellia oil production and quality.