RNAi knockdown of fatty acid elongase1 alters fatty acid composition in Brassica napus

Mechanism Analysis of Increased Erucic Acid Content in Brassica napus L. Seeds Resulting Low Nighttime Temperature

Brassica napus L. (B. napus L.), a crop of Brassica in the family Cruciferae, is a major sources of edible vegetable oil and one of the four most widely grown. Oil accumulation is determined by genetic and environmental factors, including temperature, light, humidity, edatope, latitude, and altitude. Temperature also plays a crucial part in the maturation stage. A highly temperature-sensitive line (STSL, DH0729DH0815) and weakly temperature-sensitive line (WTSL, DH0729) were used to express LOC106368911 and its effect on the erucic acid content of seeds under low nighttime temperatures. Condition of 20/18 °C (±0.5 °C, daytime/nighttime temperature, CK) and 20/13 °C (low nighttime temperature, LNT) were used in tests. Under LNT, the erucic acid content in STSL seeds increased significantly, whereas the WTSL change was not significant. The relative expression of LOC106368911 was significantly increased in STSL at 27, 35 and 43 days after flowering (DAF), whereas the change in WTSL was not significant. The CDS sequence of the LOC106368911 was cloned. Compared to the protein sequence encoded by the reference gene, STSL changed the 96th amino acid sequence from I (leucine) to L (isoleucine). However, there was no difference in the secondary and tertiary structures. Based on this, we cloned the LOC106368911 promoter sequence and found that the mutation of C to T at position -790 in WTSL caused the loss of LTR (cis-acting element involved in low-temperature responsiveness, -791 to -786) element function in response to low temperature and increased erucic acid content. The LOC106368911 promoter had 2 LTR elements in STSL (-791 to -786 and -588 to -583). A GUS reporter vector was constructed to study the transient expression in tobacco leaf transformations. GUS gene expression at 13 ℃ after 2 h was significantly higher than that at 18 ℃. Base and number differences in the LTR element were found in the LOC106368911 promoter sequence of STSL and WTSL. Base mutations occurred in the LTR element in WTSL, which resulted in decrease or loss of erucic acid content in response to low nighttime temperatures.

From fibers to flowering to metabolites: unlocking hemp (Cannabis sativa) potential with the guidance of novel discoveries and tools

Cannabis sativa L. is an ancient crop, but its agricultural adoption has been interrupted to prevent the use of marijuana as a psychoactive drug. Nevertheless, hemp-the C. sativa type with low concentrations of intoxicating Δ9-tetrahydrocannabinoid-is experiencing a resurgence in interest due to loosened cultivation restrictions and its potential as a multipurpose bio-based crop. Hemp has valuable applications, including production of medicines from its non-intoxicating cannabinoids, food, medical, and industrial uses of its seed oil rich in polyunsaturated fatty acids, and production of fibers for textiles and industry from its stems. Recently, several hemp genomic and genetic resources have been developed, allowing significant expansion of our knowledge of major hemp traits, such as synthesis of cannabinoids, oil, and fibers, and regulation of flowering and sex determination. Still, hemp is an underimproved crop, and its development will depend on the ability to expand and collectively use the novel resources arising from fast advancements in bioinformatics and plant phenotyping. This review discusses current genetic and genomic knowledge of the most important hemp traits, and provides a perspective on how to further expand such knowledge and tackle hemp improvement with the most up-to-date tools for plant and hemp research.

Transcriptome Analysis of Maize Ear Leaves Treated with Long-Term Straw Return plus Nitrogen Fertilizer under the Wheat-Maize Rotation System

Straw return (SR) plus nitrogen (N) fertilizer has become a practical field management mode to improve soil fertility and crop yield in North China. This study aims to explore the relationship among organic waste, mineral nutrient utilization, and crop yield under SRN mode. The fertilizer treatments included unfertilized (CK), SR (straws from wheat and corn), N fertilizer (N), and SR plus N fertilizer (SRN). SRN treatment not only significantly increased the grain yield, net photosynthetic rate, and transpiration rate but also enhanced the contents of chlorophyll, soluble sugar, and soluble protein and increased the activities of antioxidant enzymes but reduced intercellular CO2 concentration and malondialdehyde (MDA) content when compared to other treatments. There were 2572, 1258, and 3395 differentially expressed genes (DEGs) identified from the paired comparisons of SRvsCK, NvsCK, and SRNvsCK, respectively. The transcript levels of many promising genes involved in the transport and assimilation of potassium, phosphate, and nitrogen, as well as the metabolisms of sugar, lipid, and protein, were down-regulated by straw returning under N treatment. SRN treatment maintained the maximum maize grain yield by regulating a series of genes' expressions to reduce nutrient shortage stress and to enhance the photosynthesis of ear leaves at the maize grain filling stage. This study would deepen the understanding of complex molecular mechanisms among organic waste, mineral nutrient utilization, crop yield, and quality.

A review on the identification of transgenic oilseeds and oils

Transgenic technology can increase the quantity and quality of vegetable oils worldwide. However, people are skeptical about the safety of transgenic oil-bearing crops and the oils they produce. In order to protect consumers' rights and avoid transgenic oils being adulterated or labeled as nontransgenic oils, the transgenic detection technology of oilseeds and oils needs careful consideration. This paper first summarized the current research status of transgenic technologies implemented at oil-bearing crops. Then, an inspection process was proposed to detect a large number of samples to be the subject rapidly, and various inspection strategies for transgenic oilseeds and oils were summarized according to the process sequence. The detection indicators included oil content, fatty acid, triglyceride, tocopherol, and nucleic acid. The detection technologies involved chromatography, spectroscopy, nuclear magnetic resonance, and polymerase chain reaction. It is hoped that this article can provide crucial technical reference and support for staff engaging in the supervision of transgenic food and for researchers developing fast and efficient monitoring methods in the future.

NM, Jebakani K. S, Selvaraj S, Pramitha J. L, Selvaraj R, Petchiammal K. I, Kather Sheriff S, Thinakaran J, Rathinamoorthy S, Kumar P. R. Genetic manipulation of anti-nutritional factors in major crops for a sustainable diet in future

The consumption of healthy food, in order to strengthen the immune system, is now a major focus of people worldwide and is essential to tackle the emerging pandemic concerns. Moreover, research in this area paves the way for diversification of human diets by incorporating underutilized crops which are highly nutritious and climate-resilient in nature. However, although the consumption of healthy foods increases nutritional uptake, the bioavailability of nutrients and their absorption from foods also play an essential role in curbing malnutrition in developing countries. This has led to a focus on anti-nutrients that interfere with the digestion and absorption of nutrients and proteins from foods. Anti-nutritional factors in crops, such as phytic acid, gossypol, goitrogens, glucosinolates, lectins, oxalic acid, saponins, raffinose, tannins, enzyme inhibitors, alkaloids, β-N-oxalyl amino alanine (BOAA), and hydrogen cyanide (HCN), are synthesized in crop metabolic pathways and are interconnected with other essential growth regulation factors. Hence, breeding with the aim of completely eliminating anti-nutrition factors tends to compromise desirable features such as yield and seed size. However, advanced techniques, such as integrated multi-omics, RNAi, gene editing, and genomics-assisted breeding, aim to breed crops in which negative traits are minimized and to provide new strategies to handle these traits in crop improvement programs. There is also a need to emphasize individual crop-based approaches in upcoming research programs to achieve smart foods with minimum constraints in future. This review focuses on progress in molecular breeding and prospects for additional approaches to improve nutrient bioavailability in major crops.

Effects of Low Nighttime Temperature on Fatty Acid Content in Developing Seeds from Brassica napus L. Based on RNA-Seq and Metabolome

Brassica napus L. is a vital plant oil resource worldwide. The fatty acid biosynthesis and oil accumulation in its seeds are controlled by several genetic and environmental factors, including daytime and nighttime temperatures. We analyzed changes in oleic and erucic acid content in two double haploid (DH) lines, DH0729, a weakly temperature-sensitive line, and DH0815, a strongly temperature-sensitive line, derived from B. napus plants grown at different altitudes (1600, 1800, 2000, 2200, and 2400 m a.s.l., 28.85° N, 112.35° E) and nighttime temperatures (20/18, 20/16, 20/13 and 20/10 °C, daytime/nighttime temperature). Based on medium- and long-chain fatty acid metabolites, the total oleic acid content 35 and 43 days after flowering was significantly lower in low nighttime temperature (LNT, 20/13 °C) plants than in high nighttime temperature (HNT, 20/18 °C) plants (HNT: 58-62%; LNT: 49-54%; an average decrease of 9%), and the total erucic acid content was significantly lower in HNT than in LNT plants (HNT: 1-2%; LNT: 8-13%; an average increase of 10%). An RNA-seq analysis showed that the expression levels of SAD (LOC106366808), ECR (LOC106396280), KCS (LOC106419344), KAR (LOC106367337), HB1(LOC106430193), and DOF5 (LOC111211868) in STSL seeds increased under LNT conditions. In STSL seeds, a base mutation in the cis-acting element involved in low-temperature responsiveness (LTR), the HB1 and KCS promoter caused loss of sensitivity to low temperatures, whereas that of the KCS promoter caused increased sensitivity to low temperatures.

CRISPR/Cas9-mediated editing of double loci of BnFAD2 increased the seed oleic acid content of rapeseed (Brassica napus L.)

Seed oleic acid is an important quality trait sought in rapeseed breeding programs. Many methods exist to increase seed oleic acid content, such as the CRISPR/Cas9-mediated genome editing system, yet there is no report on seed oleic acid content improvement via this system's precise editing of the double loci of BnFAD2. Here, a precise CRISPR/Cas9-mediated genome editing of the encoded double loci (A5 and C5) of BnFAD2 was established. The results demonstrated high efficiency of regeneration and transformation, with the rapeseed genotype screened in ratios of 20.18% and 85.46%, respectively. The total editing efficiency was 64.35%, whereas the single locus- and double locus-edited ratios were 21.58% and 78.42%, respectively. The relative proportion of oleic acid with other fatty acids in seed oil of mutants was significantly higher for those that underwent the editing on A5 copy than that on C5 copy, but it was still less than 80%. For double locus-edited mutants, their relative proportion of oleic acid was more than 85% in the T₁ and T₄ generations. A comparison of the sequences between the double locus-edited mutants and reference showed that no transgenic border sequences were detected from the transformed vector. Analysis of the BnFAD2 sequence on A5 and C5 at the mutated locus of double loci mutants uncovered evidence for base deletion and insertion, and combination. Further, no editing issue of FAD2 on the copy of A1 was detected on the three targeted editing regions. Seed yield, yield component, oil content, and relative proportion of oleic acid between one selected double loci-edited mutant and wild type were also compared. These results showed that although the number of siliques per plant of the wild type was significantly higher than those of the mutant, the differences in seed yield and oil content were not significant between them, albeit with the mutant having a markedly higher relative proportion of oleic acid. Altogether, our results confirmed that the established CRISPR/Cas9-mediated genome editing of double loci (A5 and C5) of the BnFAD2 can precisely edit the targeted genes, thereby enhancing the seed oleic acid content to a far greater extent than can a single locus-editing system.

CRISPR/Cas9-Mediated Gene Editing of BnFAD2 and BnFAE1 Modifies Fatty Acid Profiles in Brassica napus

Fatty acid (FA) composition determines the quality of oil from oilseed crops, and thus is a major target for genetic improvement. FAD2 (Fatty acid dehydrogenase 2) and FAE1 (fatty acid elongase 1) are critical FA synthetic genes, and have been the focus of genetic manipulation to alter fatty acid composition in oilseed plants. In this study, to improve the nutritional quality of rapeseed cultivar CY2 (about 50% oil content; of which 40% erucic acid), we generated novel knockout plants by CRISPR/Cas9 mediated genome editing of BnFAD2 and BnFAE1 genes. Two guide RNAs were designed to target one copy of the BnFAD2 gene and two copies of the BnFAE1 gene, respectively. A number of lines with mutations at three target sites of BnFAD2 and BnFAE1 genes were identified by sequence analysis. Three of these lines showed mutations in all three target sites of the BnFAD2 and BnFAE1 genes. Fatty acid composition analysis of seeds revealed that mutations at all three sites resulted in significantly increased oleic acid (70–80%) content compared with that of CY2 (20%), greatly reduced erucic acid levels and slightly decreased polyunsaturated fatty acids content. Our results confirmed that the CRISPR/Cas9 system is an effective tool for improving this important trait.

A Review of Erucic Acid Production in Brassicaceae Oilseeds: Progress and Prospects for the Genetic Engineering of High and Low-Erucic Acid Rapeseeds (Brassica napus)

Erucic acid (C22:1, ω-9, EA) is a very-long-chain monounsaturated fatty acid (FA) that is an important oleochemical product with a wide range of uses in metallurgy, machinery, rubber, the chemical industry, and other fields because of its hydrophobicity and water resistance. EA is not easily digested and absorbed in the human body, and high-EA rapeseed (HEAR) oil often contains glucosinolates. Both glucosinolates and EA are detrimental to health and can lead to disease, which has resulted in strict guidelines by regulatory bodies on maximum EA contents in oils. Increasingly, researchers have attempted to enhance the EA content in Brassicaceae oilseeds to serve industrial applications while conversely reducing the EA content to ensure food safety. For the production of both LEAR and HEAR, biotechnology is likely to play a fundamental role. Elucidating the metabolic pathways of EA can help inform the improvement of Brassicaceae oilseeds through transgenic technology. In this paper, we introduce the industrial applications of HEAR oil and health benefits of low-EA rapeseed (LEAR) oil first, following which we review the biosynthetic pathways of EA, introduce the EA resources from plants, and focus on research related to the genetic engineering of EA in Brassicaceae oilseeds. In addition, the effects of the environment on EA production are addressed, and the safe cultivation of HEAR and LEAR is discussed. This paper supports further research into improving FAs in Brassicaceae oilseeds through transgenic technologies and molecular breeding techniques, thereby advancing the commercialization of transgenic products for better application in various fields.

Plant monounsaturated fatty acids: Diversity, biosynthesis, functions and uses

Monounsaturated fatty acids are straight-chain aliphatic monocarboxylic acids comprising a unique carbon‑carbon double bond, also termed unsaturation. More than 50 distinct molecular structures have been described in the plant kingdom, and more remain to be discovered. The evolution of land plants has apparently resulted in the convergent evolution of non-homologous enzymes catalyzing the dehydrogenation of saturated acyl chain substrates in a chemo-, regio- and stereoselective manner. Contrasted enzymatic characteristics and different subcellular localizations of these desaturases account for the diversity of existing fatty acid structures. Interestingly, the location and geometrical configuration of the unsaturation confer specific characteristics to these molecules found in a variety of membrane, storage, and surface lipids. An ongoing research effort aimed at exploring the links existing between fatty acid structures and their biological functions has already unraveled the importance of several monounsaturated fatty acids in various physiological and developmental contexts. What is more, the monounsaturated acyl chains found in the oils of seeds and fruits are widely and increasingly used in the food and chemical industries due to the physicochemical properties inherent in their structures. Breeders and plant biotechnologists therefore develop new crops with high monounsaturated contents for various agro-industrial purposes.

Development of B. carinata with super-high erucic acid content through interspecific hybridization

KEY MESSAGE

Disomic alien chromosome addition Brassica carinata lines with super-high erucic acid content were developed through interspecific hybridization with B. juncea and characterized using molecular, cytological and biochemical techniques. Brassica carinata [A.] Braun (BBCC, 2n = 34) is a climate-resilient oilseed. Its seed oil is high in erucic acid (> 40%), rendering it well suited for the production of biofuel and other bio-based applications. To enhance the competitiveness of B. carinata with high erucic B. napus (HEAR), lines with super-high erucic acid content were developed through interspecific hybridization. To this end, a fad2B null allele from Brassica juncea (AABB, 2n = 36) was introgressed into B. carinata, resulting in a B. carinata fad2B mutant with erucic acid levels of over 50%. Subsequently, the FAE allele from B. rapa spp. yellow sarson (AA, 2n = 20) was transferred to the fad2B B. carinata line, yielding lines with erucic acid contents of up to 57.9%. Molecular analysis using the Brassica 90 K Illumina Infinium™ SNP genotyping array identified these lines as disomic alien chromosome addition lines, with two extra A08 chromosomes containing the BrFAE gene. The alien chromosomes from B. rapa were clearly distinguished by molecular cytogenetics in one of the addition lines. Analysis of microspore-derived offspring and hybrids from crosses with a CMS B. carinata line showed that the transfer rate of the A08 chromosome into male gametes was over 98%, resulting in almost completely stable transmission of an A08 chromosome copy into the progeny. The increase in erucic acid levels was accompanied by changes in the proportions of other fatty acids depending on the genetic changes that were introduced in the interspecific hybrids, providing valuable insights into erucic acid metabolism in Brassica.

Recent advances in enhancement of oil content in oilseed crops

Plant oils are very valuable agricultural commodity. The manipulation of seed oil composition to deliver enhanced fatty acid compositions, which are appropriate for feed or fuel, has always been a main objective of metabolic engineers. The last two decennary have been noticeable by numerous significant events in genetic engineering for identification of different gene targets to improve oil yield in oilseed crops. Particularly, genetic engineering approaches have presented major breakthrough in elevating oil content in oilseed crops such as Brassica napus and soybean. Additionally, current research efforts to explore the possibilities to modify the genetic expression of key regulators of oil accumulation along with biochemical studies to elucidate lipid biosynthesis will establish protocols to develop transgenic oilseed crops along much improved oil content. In this review, we describe current distinct genetic engineering approaches investigated by researchers for ameliorating oil content and its nutritional quality. Moreover, we will also discuss some auspicious and innovative approaches and challenges for engineering oil content to yield oil at much higher rate in oilseed crops.

Depressed expression of FAE1 and FAD2 genes modifies fatty acid profiles and storage compounds accumulation in Brassica napus seeds

In plants, the enzymes fatty acid dehydrogenase 2 (FAD2) and fatty acid elongase 1 (FAE1) have been shown in previous studies to play important roles in the de novo biosynthesis of fatty acids. However, the effects of depressed expression of FAD2 and FAE1 on seed storage compounds accumulation remains to be elucidated. In this study, we produced RNA interfering transgenic rapeseeds lines, BnFAD2-Ri, BnFAE1-Ri and BnFAD2/BnFAE1-Ri, which exhibited depressed expression of the BnFAD2 and BnFAE1 genes under the control of seed-specific napin A promoter. These transgenic rapeseeds showed normal growth and development as compared with the wild type (CY2). Depressed expression of BnFAD2 and BnFAE1 genes modified fatty acid profiles, leading to increased oleic acid and decreased erucic acid contents in transgenic seeds. Consistent with these results, the ratios of C18:1/C18:2 and C18:1/C18:3 in C18 unsaturated fatty acids were greatly increased due to increased oleic acid content in transgenic seeds. Moreover, depressed expression of BnFAD2 and BnFAE1 genes resulted in slightly decreased oil contents and increased protein contents in transgenic seeds. Our results demonstrated that depressed expression of BnFAD2 and BnFAE1 greatly improves seed nutritional quality by modulating the fatty acid metabolism and storage products accumulation and that BnFAD2 and BnFAE1 are reliable targets for genetic improvement of rapeseed in seed nutritional quality.

Significant increase of oleic acid level in the wild species Lepidium campestre through direct gene silencing

Simultaneous RNAi silencing of the FAD2 and FAE1 genes in the wild species Lepidium campestre improved the oil quality with 80 % oleic acid content compared to 11 % in wildtype. Field cress (Lepidium campestre) is a wild biennial species within the Brassicaceae family with desirable agronomic traits, thus being a good candidate for domestication into a new oilseed and catch crop. However, it has agronomic traits that need to be improved before it can become an economically viable species. One of such traits is the seed oil composition, which is not desirable either for food use or for industrial applications. In this study, we have, through metabolic engineering, altered the seed oil composition in field cress into a premium oil for food processing, industrial, or chemical industrial applications. Through seed-specific RNAi silencing of the field cress fatty acid desaturase 2 (FAD2) and fatty acid elongase 1 (FAE1) genes, we have obtained transgenic lines with an oleic acid content increased from 11 % in the wildtype to over 80 %. Moreover, the oxidatively unstable linolenic acid was decreased from 40.4 to 2.6 %, and the unhealthy erucic acid was reduced from 20.3 to 0.1 %. The high oleic acid trait has been kept stable for three generations. This shows the possibility to use field cress as a platform for genetic engineering of oil compositions tailor-made for its end uses.