Genetic engineering approaches to enhance oil content in oilseed crops

Oilseed crops play an important role in the agricultural economy. Apart from being an integral component of human diet and industrial applications, they are also gaining importance as replacement to fossil fuels for meeting the energy needs. The last two decades have been marked by several important events in genetic engineering and identification of gene targets for enhancing seed oil content in oilseed crops, and will aid the successful development of new generation high yielding oil crops. Specifically, genetic engineering has shown real breakthrough in enhancing oil content in oilseed rape, camelina, soybean and maize. Moreover, ongoing research efforts to decipher the possibilities of genetic modifications of key regulators of oil accumulation along with physiological and biochemical studies to understand lipid biosynthesis will set a platform to produce transgenic oilseed crops with enhanced oil content. In this review, we briefly describe different genetic engineering approaches explored by different researchers for enhancing oil content. Further, we discuss a few promising and potential approaches and challenges for engineering oil content in oilseed crops.     

Expression of Umbelopsis ramanniana DGAT2A in seed increases oil in soybean

Oilseeds are the main source of lipids used in both food and biofuels. The growing demand for vegetable oil has focused research toward increasing the amount of this valuable component in oilseed crops. Globally, soybean (Glycine max) is one of the most important oilseed crops grown, contributing about 30% of the vegetable oil used for food, feed, and industrial applications. Breeding efforts in soy have shown that multiple loci contribute to the final content of oil and protein stored in seeds. Genetically, the levels of these two storage products appear to be inversely correlated with an increase in oil coming at the expense of protein and vice versa. One way to overcome the linkage between oil and protein is to introduce a transgene that can specifically modulate one pathway without disrupting the other. We describe the first, to our knowledge, transgenic soy crop with increased oil that shows no major impact on protein content or yield. This was achieved by expressing a codon-optimized version of a diacylglycerol acyltransferase 2A from the soil fungus Umbelopsis (formerly Mortierella) ramanniana in soybean seed during development, resulting in an absolute increase in oil of 1.5% (by weight) in the mature seed.     

Studies on beet western yellows virus in oilseed rape (Brassica napus ssp. oleifera) and sugar beet (Beta vulgaris)

Oilseed rape (Brassica napus L. ssp. oleifera) was studied as a potential overwintering host for the sugar-beet yellowing viruses, beet yellows virus (BYV) and beet mild yellowing virus (BMYV), and their principal vector, Myzus persicae. In spring 1982, plants infected with a virus which reacted positively in enzyme-linked immunosorbent assay (ELISA) with BMYV antibody globulin were found in oilseed-rape crops; none of the plants contained virus which reacted with BYV antibody globulin. This virus was subsequently identified as beet western yellows virus (BWYV). No leaf symptoms could be consistently associated with infection of oilseed rape, but the virus was reliably detected by sampling any leaf on an infected oilseed-rape plant. Some isolates from oilseed rape did infect sugar beet in glasshouse tests, but the proportions of inoculated plants which became infected were low. Apparently there is therefore little danger of much direct transmission of BWYV by M. persicae from oilseed rape to sugar beet in spring. BWYV was introduced to and spread within oilseed-rape crops in autumn by M. persicae, and autumn-sown oilseed rape proved to be a potentially important overwintering host for M. persicae. In a survey of 80 autumn-sown crops of oilseed rape in East Anglia, northern England and Scotland in spring 1983, 78 were shown to be extensively infected with BWYV. Experimental plots of oilseed rape with 100% BWYV-infection yielded approximately 13.4% less oil than plots with 18% virus infection, the result of a decrease in both seed yield and oil content.     

The application of genetic engineering to oilseed crops

Increasing attention is being given to the prospects for the genetic engineering of oilseed crops, both in the industrial and academic sectors. The process of creating genetically stable new crops with desirable vegetable oil composition and content is necessarily complex. The modification of seed storage lipids appears to be feasible and there exists a broad knowledge base on lipid biosynthetic enzymes, but applied research and product development will depend on gaining a better understanding of the biochemical bases of lipid biosynthesis.     

基因工程在改善植物油营养价值中的应用

本文介绍了近年来应用基因工程技术对植物油的脂肪酸成分进行改造,进而生产有益于健康的食用油所取得的进展.近10年来,应用基因修饰的方法对植物油进行营养学方面的改良已经取得了很大的进展,随着植物脂肪酸生物合成途径的日趋明确,通过转基因技术可以让植物生产许多含有特殊脂肪酸成分且对人类健康有益的植物油.     

基因工程在改善植物油营养价值中的应用

本文介绍了近年来应用基因工程技术对植物油的脂肪酸成分进行改造, 进而生产有益于健康的食用油所取得的进展。近10年来, 应用基因修饰的方法对植物油进行营养学方面的改良已经取得了很大的进展, 随着植物脂肪酸生物合成途径的日趋明确, 通过转基因技术可以让植物生产许多含有特殊脂肪酸成分且对人类健康有益的植物油。     

Utilization of commercial oilseed crops

The United States is a major producer of many different types of oilseeds, but the predominant one is soybean, that remarkable legume whose meal and oil serve many animal feed, human food, and domestic industrial product needs. More than half of the soybeans and the products produced from them are exported. The 16 mill MT of soy meal processed and fed in the United States in 1981 constituted 88% of the total oilseed meal, 71% of the high-protein feeds, and 48% of total processed feeds. Of the total soy protein available, less than 5% goes into human food products such as meat extenders, simulated meats, baked goods, dairy product analogs, dietary foods, infant foods, and fermented food products. Less than 1% of soy protein in the United States is used in industrial products, mainly as a binder for pigmented paper coatings. Of the total soy oil available, about 95% is consumed in food products such as margarines, salad oils, and cooking oils. About 5% of soy oil is applied to nonfood uses such as alkyd paints, plasticizer/stabilizers for vinyl plastics, soaps, eraser factices, and many other lesser uses. Other major oilseeds produced in the United States include cottonseed, flaxseed, peanut, safflower, and sunflower. Corn oil is produced in significant quantities as a by-product of the corn starch industry. The oilseed crops having the greatest oil productivity are peanut and sunflower. However, sunflower meal has certain deficiencies for feed and food uses. If the United States is to draw upon oilseed crops as significant contributors to feed, food, industrial products, and agricultural fuel needs, greatly improved productivity will be needed either from new oilseed crops or from improved varieties of present commercial crops.     

Production of nutritionally desirable fatty acids in seed oil of Indian mustard (Brassica juncea L.) by metabolic engineering

Development of a designer oilseed crop with improved yield attributes and enhanced nutritional quality for the benefits of mankind and animal husbandry is now achievable with the combination of genetic engineering and plant breeding. In spite of their immense importance, the fatty acid profiles of most oilseed crops are imbalanced that necessitate the use of metabolic engineering strategies to overcome the various shortfalls in order to improve the nutritional quality of these edible oils. Indian mustard (Brassica juncea L.), being one of the important oilseed crops in Indian subcontinent naturally contains ~50 % nutritionally undesirable very long chain unsaturated fatty acids (VLCUFAs), e.g. erucic acid (C_22:1). For the purpose of nutritional improvement of B. juncea seed oil, several metabolic engineering strategies have been employed to divert the carbon flux from the production of VLCUFAs to other important fatty acids. Stearic acid, being a saturated but nutritionally neutral fatty acid, is naturally inadequate in most of the conventional oil seeds. Due to its neutral effect on consumer’s health and as an important industrial ingredient, increased in planta production of stearic acid in the seed oil not only helps in reduction of production cost but also lessens the trans fatty acid production during commercial hydrogenation process. In this review metabolic engineering strategies to minimize the VLCUFAs along with increased production of stearic acid in the seed oil of B. juncea are discussed, so that further breeding attempts can be made to improve the nutritionally desirable fatty acid profile in the suitable cultivars of this important oilseed crop.     

Bioenergetic considerations in the improvement of oil content and quality in oil-seed crops

Summary Production values (PVs), defined as the weight of the end product/weight of the substrate required for carbon skeletons and energy production, were calculated for plant fatty acids. The PVs varied from 0.361 to 0.300 with linolenic acid having the lowest value. In general, the PVs of unsaturated fatty acids were lower than those of saturated fatty acids of similar chain lengths. Using this basic information, PVs of (A) oils from different oilseed crops, based on their standard fatty acid composition and (B) seed biomass with specified oil content and fatty acid composition were calculated. 1/PV gives the glucose required for the biosynthesis of 1 g end product and thus an estimate of the photosynthate requirement for the desired breeding goal can be estimated. Such calculations show that increasing oil percentage in seeds has a maximum energy cost when the increase in oil is associated with a decrease in the amount of carbohydrates where there is no change in protein concentration. Reduction of erucic acid content in the rapeseed oil did not alter its PV. It is inferred that there are no serious bioenergetic constraints in altering the fatty acid composition.     

Assessment of sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.<Emphasis Type="Bold">)</Emphasis> cake as a source of high-added value substances: from waste to health

The risk of exhaustion of natural resources and raw materials have given rise to emerging trends such as recycling of food waste. From the economical and ecological points of view, conversion of biowaste to high added value compounds has been getting great attention among the science and commercial entities. Due to their high-added value phytochemicals, agricultural and food residues have been a great significant to the researchers around the world. This study focuses on the valorisation of cake derived from sesame oil processing. If the very valuable non-nutrient phytochemicals in sesame cake are not evaluated properly, they would be consumed as just animal feed or fertilizers. They might be employed as antiaging (in pharmaceutical products), or free radical scavenger (in dietary supplements), or preservative additive against lipid oxidation (in fat containing food products). This review article aims to present pharmacological and therapeutic effects of sesame cake extract by pointing out its application in pharmaceutical, cosmetic and food industries.     

Agricultural production of halophytes irrigated with seawater

Summary Growing agricultural crops with direct seawater irrigation has progressed within the past few years from the conceptual to the experimental phase. This has been accomplished by selecting halophytes with inherently high salinity tolerance for use as crop plants rather than by increasing the ability of traditional crop plants to tolerate seawater. Some of the halophytes being investigated for use as crops in seawater irrigation scenarios have high nutritional value as forage or fodder crops. Most of them also have high digestibility. The limiting factor in such use is their high salt content, but this limitation can be moderated. However, since seeds of halophytes do not accumulate salt any more than do those of glycophytes, the greatest promise for seawater-irrigated halophytes probably will be as seed crops. The seeds of many halophytes have high protein and oil contents and compare favorably with traditional oilseed crops. Sustained high yields of seed and biomass already have been obtained from some halophytes irrigated with seawater, and within the next few years seawater agriculture should proceed from the experimental to the operational phase.     

Cloning, sequencing and salt induced expression of PEAMT and BADH in oilseed rape (Brassica napus).

Agriculture productivity is severely hampered by soil salinity, drought and other environmental stresses. Studies on stress-resistant plants (halophytes, xerophytes, accumulating plants for specific toxic ions) have illuminated some mechanisms of stress tolerance in plants at metabolic or molecular levels, which gave some clues on how to genetically engineer stress-tolerant crops. With the isolation of more stress-responsive genes, genetic engineering with modified expression of stress responsive genes may be an effective way to produce stress-tolerant crops. In the present report, two genes (PEAMT and BADH) encoding the corresponding key enzymes for choline and glycine betaine (an important osmoprotectant) biosynthesis in plants were isolated in oilseed rape, an important oil crop in the world. Effects of salt stress on their expression were studied with quantitative PCR and their potential use in the genetic engineering of oilseed rape was discussed.     

Strategies for recycling and valorization of grape marc

Grapes are one of the most cultivated fruit crops worldwide. Either for wine or juice production, grape processing generates a large amount of residues that must be treated, disposed of or reused properly to reduce their pollution load before being applied to the soil. In this review, a special focus is given to the treatment and valorization of the winemaking by-product like grape marc via anaerobic digestion, composting and vermicomposting at laboratory, pilot, and industrial scales. The impact of the final products (digestates, composts, and vermicomposts) on soil properties is briefly addressed. Moreover, the role of grape marc and seeds as a valuable source of natural phytochemicals that include polyphenols and other bioactive compounds of interest for pharmaceutical, cosmetic, and food industries is also discussed. This is of paramount importance given the fact that sustainability requires the use of management and valorization strategies that allow the recovery of valuable compounds (e.g. antioxidants) with minimum disposal of waste streams.     

Oil crops: From the classical traits to genetic improvement

Soybean, oilseed rape, peanut, and so on, are important resources of vegetable oil for human beings. Cultivation and production of these oil crops are expected to increase due to continuous population growth, which poses a challenge to the genetic improvement of oil crops. With reference genomes of several oil crops sequenced and genetic transformation and gene editing tools readily available, the basic and applied researches of oil crops come to a functional genomic era integrating multiple approaches.     

Comparative processing practices of the world’s major oilseed crops

The major oilseed crops were domesticated primarily as sources of edible oil. However, in all cases, yields of by-products are greater than the oil fraction, and, in reality, all oilseed crops serve dual purposes as sources of oil and of protein for human food, animal feed, and industrial products. Each crop has special requirements for extraction and for processing of oil and meal, and each has limitations as to location and timing of production and as to processibility in oil mills originally designed for other crops. Further, each oilseed has unique cultural, economic and utilization characteristics; for example, rapeseed (Brassica) can be grown in cool climates with short growing seasons. Cottonseed (Gossypium) is a by-product of the more valuable fiber crop, and its availability is dictated by the profitability of growing cotton for the world market. Although peanuts (Arachis hypogaea) are used primarily as peanut butter and nuts in the United States, they are almost exclusively pressed for oil in other countries. In this paper, cultural practices and processing requirements of soybean (Glycine max), cottonseed, sunflower (Helianthus annuus), rapeseed, peanut, and sesame (Sesamum indicum) oils and byproducts are compared, as well as compositions of major oilmilling fractions, oils and proteins.     

Functional Analysis of Sesame Diacylglycerol Acyltransferase and Phospholipid: Diacylglycerol Acyltransferase Genes Using In Silico and In Vitro Approaches

Plant Molecular Biology Reporter - Sesamum indicum L. is one of the major oilseed crops of India. Sesame oil is stable with a good source of unsaturated fatty acids. To know the mechanism of oil...     

Suppression of the SUGAR‐DEPENDENT1 triacylglycerol lipase family during seed development enhances oil yield in oilseed rape (Brassica napus L.)

Increasing the productivity of oilseed crops is an important challenge for plant breeders and biotechnologists. To date, attempts to increase oil production in seeds via metabolic pathway engineering have focused on boosting synthetic capacity. However, in the tissues of many organisms, it is well established that oil levels are determined by both anabolism and catabolism. Indeed, the oil content of rapeseed (Brassica napus L.) has been reported to decline by approximately 10% in the final stage of development, as the seeds desiccate. Here, we show that RNAi suppression of the SUGAR‐DEPENDENT1 triacylglycerol lipase gene family during seed development results in up to an 8% gain in oil yield on either a seed, plant or unit area basis in the greenhouse, with very little adverse impact on seed vigour. Suppression of lipolysis could therefore constitute a new method for enhancing oil yield in oilseed crops.     

Metabolic engineering of fatty acid biosynthesis in plants.

Fatty acids are the most abundant form of reduced carbon chains available from nature and have diverse uses ranging from food to industrial feedstocks. Plants represent a significant renewable source of fatty acids because many species accumulate them in the form of triacylglycerol as major storage components in seeds. With the advent of plant transformation technology, metabolic engineering of oilseed fatty acids has become possible and transgenic plant oils represent some of the first successes in design of modified plant products. Directed gene down-regulation strategies have enabled the specific tailoring of common fatty acids in several oilseed crops. In addition, transfer of novel fatty acid biosynthetic genes from noncommercial plants has allowed the production of novel oil compositions in oilseed crops. These and future endeavors aim to produce seeds higher in oil content as well as new oils that are more stable, are healthier for humans, and can serve as a renewable source of industrial commodities. Large-scale new industrial uses of engineered plant oils are on the horizon but will require a better understanding of factors that limit the accumulation of unusual fatty acid structures in seeds.     

Expansion of mass-flowering crops leads to transient pollinator dilution and reduced wild plant pollination

Agricultural land use results in direct biodiversity decline through loss of natural habitat, but may also cause indirect cross-habitat effects on conservation areas. We conducted three landscape-scale field studies on 67 sites to test the hypothesis that mass flowering of oilseed rape (Brassica napus) results in a transient dilution of bees in crop fields, and in increased competition between crop plants and grassland plants for pollinators. Abundances of bumble-bees, which are the main pollinators of the grassland plant Primula veris, but also pollinate oilseed rape (OSR), decreased with increasing amount of OSR. This landscape-scale dilution affected bumble-bee abundances strongly in OSR fields and marginally in grasslands, where bumble-bee abundances were generally low at the time of Primula flowering. Seed set of Primula veris, which flowers during OSR bloom, was reduced by 20 per cent when the amount of OSR within 1 km radius increased from 0 to 15 per cent. Hence, the current expansion of bee-attractive biofuel crops results in transient dilution of crop pollinators, which means an increased competition for pollinators between crops and wild plants. In conclusion, mass-flowering crops potentially threaten fitness of concurrently flowering wild plants in conservation areas, despite the fact that, in the long run, mass-flowering crops can enhance abundances of generalist pollinators and their pollination service.