Cellular Plasticity in Response to Suppression of Storage Proteins in the Brassica napus Embryo

The look insight - magnetic resonance imaging (MRI) of the inner life of plants

Magnetic resonance imaging (MRI) is one of the most versatile and widely used imaging techniques in modern medicine, but its incredible potential remains underutilized in plant science. Many aspects of the inner life of plants are still unknown and are waiting to be discovered by new innovative technological solutions. The ability of MRI to non-invasively explore processes inside living organisms offers an unparalleled opportunity to investigate metabolism, nutrient allocation, growth and development. Enabling the visualization of complex dynamics in living organisms in unprecedented ways could transform how we study and perceive plants. This article highlights the critical advancements and strategies that are paving the way for MRI to become an essential tool in plant research, unlocking new frontiers in biology and agriculture.

A multi-omics approach reveals a link between ribosomal protein alterations and proteome rebalancing in Arabidopsis thaliana seeds

The ability of seeds to restore their amino acid content and composition after the elimination of the most abundant seed storage proteins (SSPs) is well-documented, yet the underlying mechanisms remain unclear. To better understand how seeds compensate for major proteomic disruptions, we conducted a comprehensive analysis on an Arabidopsis mutant lacking the three most abundant SSPs, the cruciferins. Our initial findings indicated that carbon, nitrogen, and sulfur levels, as well as total protein and oil content, remained unchanged in these mutants suggesting rebalanced seeds. Transcriptomics and proteomics performed during seed maturation of Col-0 and the triple mutant revealed significant modulation in many components of the translational machinery, especially ribosomal proteins (RPs), and in the antioxidation response in the mutant. These findings suggest that RPs play a critical role in facilitating proteomic homeostasis during seed maturation when proteomic perturbation occurs. Biochemical and metabolic analyses of the triple mutant dry seeds revealed increased protein carbonylation and elevated glutathione levels further supporting the link between SSP accumulation and seed redox homeostasis. Overall, we propose that in response to significant proteomic perturbations, changes in the proteome and amino acid composition of seeds are accompanied by a broad remodeling of the translation apparatus. We postulate that these alterations are key elements in seed adaptability and robustness to large proteomic perturbations during seed maturation.

Breeding and biotechnology approaches to enhance the nutritional quality of rapeseed byproducts for sustainable alternative protein sources- a critical review

Global protein consumption is increasing exponentially, which requires efficient identification of potential, healthy, and simple protein sources to fulfil the demands. The existing sources of animal proteins are high in fat and low in fiber composition, which might cause serious health risks when consumed regularly. Moreover, protein production from animal sources can negatively affect the environment, as it often requires more energy and natural resources and contributes to greenhouse gas emissions. Thus, finding alternative plant-based protein sources becomes indispensable. Rapeseed is an important oilseed crop and the world's third leading oil source. Rapeseed byproducts, such as seed cakes or meals, are considered the best alternative protein source after soybean owing to their promising protein profile (30%-60% crude protein) to supplement dietary requirements. After oil extraction, these rapeseed byproducts can be utilized as food for human consumption and animal feed. However, anti-nutritional factors (ANFs) like glucosinolates, phytic acid, tannins, and sinapines make them unsuitable for direct consumption. Techniques like microbial fermentation, advanced breeding, and genome editing can improve protein quality, reduce ANFs in rapeseed byproducts, and facilitate their usage in the food and feed industry. This review summarizes these approaches and offers the best bio-nutrition breakthroughs to develop nutrient-rich rapeseed byproducts as plant-based protein sources.

Mechanical forces orchestrate the metabolism of the developing oilseed rape embryo

The initial free expansion of the embryo within a seed is at some point inhibited by its contact with the testa, resulting in its formation of folds and borders. Although less obvious, mechanical forces appear to trigger and accelerate seed maturation. However, the mechanistic basis for this effect remains unclear. Manipulation of the mechanical constraints affecting either the in vivo or in vitro growth of oilseed rape embryos was combined with analytical approaches, including magnetic resonance imaging and computer graphic reconstruction, immunolabelling, flow cytometry, transcriptomic, proteomic, lipidomic and metabolomic profiling. Our data implied that, in vivo, the imposition of mechanical restraints impeded the expansion of testa and endosperm, resulting in the embryo's deformation. An acceleration in embryonic development was implied by the cessation of cell proliferation and the stimulation of lipid and protein storage, characteristic of embryo maturation. The underlying molecular signature included elements of cell cycle control, reactive oxygen species metabolism and transcriptional reprogramming, along with allosteric control of glycolytic flux. Constricting the space allowed for the expansion of in vitro grown embryos induced a similar response. The conclusion is that the imposition of mechanical constraints over the growth of the developing oilseed rape embryo provides an important trigger for its maturation.

Seeing plants as never before

Imaging has long supported our ability to understand the inner life of plants, their development, and response to a dynamic environment. While optical microscopy remains the core tool for imaging, a suite of novel technologies is now beginning to make a significant contribution to visualize plant metabolism. The purpose of this review was to provide the scientific community with an overview of current imaging methods, which rely variously on either nuclear magnetic resonance (NMR), mass spectrometry (MS) or infrared (IR) spectroscopy, and to present some examples of their application in order to illustrate their utility. In addition to providing a description of the basic principles underlying these technologies, the review discusses their various advantages and limitations, reveals the current state of the art, and suggests their potential application to experimental practice. Finally, a view is presented as to how the technologies will likely develop, how these developments may encourage the formulation of novel experimental strategies, and how the enormous potential of these technologies can contribute to progress in plant science.

Analysis of oil synthesis pathway in Cyperus esculentus tubers and identification of oleosin and caleosin genes

The tubers of the widely distributed Cyperus esculentus are rich in oil, and therefore, the plant is considered to have a high utilization value in the vegetable oil industry. Oleosins and caleosins are lipid-associated proteins found in oil bodies of seeds; however oleosins and caleosins genes have not been identified in C. esculentus. In this study, we performed transcriptome sequencing and lipid metabolome analysis of C. esculentus tubers at four developmental stages to obtain the information on their genetic profile, expression trends, and metabolites in oil accumulation pathways. Overall, 120,881 non-redundant unigenes and 255 lipids were detected; 18 genes belonged to the acetyl-CoA carboxylase (ACC), malonyl-CoA:ACP transacylase (MCAT), β-ketoacyl-ACP synthase (KAS), and fatty acyl-ACP thioesterase (FAT) gene families involved in fatty acid biosynthesis, and 16 genes belonged to the glycerol-3-phosphate acyltransferase (GPAT), diacylglycerol acyltransferase 3 (DGAT3), phospholipid:diacylglycerol acyltransferase (PDAT), FAD2, and lysophosphatidic acid acyltransferase (LPAAT) gene families playing important roles in triacylglycerol synthesis. We also identified 9 oleosin- and 21 caleosin-encoding genes in C. esculentus tubers. These results provide detailed information on the C. esculentus transcriptional and metabolic profiles, which can be used as reference for the development of strategies to increase oil content in C. esculentus tubers.

Bioengineering of Soybean Oil and Its Impact on Agronomic Traits

Soybean is a major oil crop and is also a dominant source of nutritional protein. The 20% seed oil content (SOC) of soybean is much lower than that in most oil crops and the fatty acid composition of its native oil cannot meet the specifications for some applications in the food and industrial sectors. Considerable effort has been expended on soybean bioengineering to tailor fatty acid profiles and improve SOC. Although significant advancements have been made, such as the creation of high-oleic acid soybean oil and high-SOC soybean, those genetic modifications have some negative impacts on soybean production, for instance, impaired germination or low protein content. In this review, we focus on recent advances in the bioengineering of soybean oil and its effects on agronomic traits.

RNAi and CRISPR-Cas silencing E3-RING ubiquitin ligase AIP2 enhances soybean seed protein content

The majority of plant protein in the world's food supply is derived from soybean (Glycine max). Soybean is a key protein source for global animal feed and is incorporated into plant-based foods for people, including meat alternatives. Soybean protein content is genetically variable and is usually inversely related to seed oil content. ABI3-interacting protein 2 (AIP2) is an E3-RING ubiquitin ligase that targets the seed-specific transcription factor ABI3. Silencing both soybean AIP2 genes (AIP2a and AIP2b) by RNAi enhanced seed protein content by up to seven percentage points, with no significant decrease in seed oil content. The protein content enhancement did not alter the composition of the seed storage proteins. Inactivation of either AIP2a or AIP2b by a CRISPR-Cas9-mediated mutation increased seed protein content, and this effect was greater when both genes were inactivated. Transactivation assays in transfected soybean hypocotyl protoplasts indicated that ABI3 changes the expression of glycinin, conglycinin, 2S albumin, and oleosin genes, indicating that AIP2 depletion increased seed protein content by regulating activity of the ABI3 transcription factor protein. These results provide an example of a gene-editing prototype directed to improve global food security and protein availability in soybean that may also be applicable to other protein-source crops.

Removing the major allergen Bra j I from brown mustard (Brassica juncea) by CRISPR/Cas9

Food allergies are a major health issue worldwide. Modern breeding techniques such as genome editing via CRISPR/Cas9 have the potential to mitigate this by targeting allergens in plants. This study addressed the major allergen Bra j I, a seed storage protein of the 2S albumin class, in the allotetraploid brown mustard (Brassica juncea). Cotyledon explants of an Indian gene bank accession (CR2664) and the German variety Terratop were transformed using Agrobacterium tumefaciens harboring binary vectors with multiple single guide RNAs to induce either large deletions or frameshift mutations in both Bra j I homoeologs. A total of 49 T₀ lines were obtained with up to 3.8% transformation efficiency. Four lines had large deletions of 566 up to 790 bp in the Bra j IB allele. Among 18 Terratop T₀  lines, nine carried indels in the targeted regions. From 16 analyzed CR2664 T₀  lines, 14 held indels and three had all four Bra j I alleles mutated. The majority of the CRISPR/Cas9-induced mutations were heritable to T₁ progenies. In some edited lines, seed formation and viability were reduced and seeds showed a precocious development of the embryo leading to a rupture of the testa already in the siliques. Immunoblotting using newly developed Bra j I-specific antibodies revealed the amount of Bra j I protein to be reduced or absent in seed extracts of selected lines. Removing an allergenic determinant from mustard is an important first step towards the development of safer food crops.

Phytoglobin-NO cycle and AOX pathway play a role in anaerobic germination and growth of deepwater rice

An important and interesting feature of rice is that it can germinate under anoxic conditions. Though several biochemical adaptive mechanisms play an important role in the anaerobic germination of rice but the role of phytoglobin-nitric oxide cycle and alternative oxidase pathway is not known, therefore in this study we investigated the role of these pathways in anaerobic germination. Under anoxic conditions, deepwater rice germinated much higher and rapidly than aerobic condition and the anaerobic germination and growth were much higher in the presence of nitrite. The addition of nitrite stimulated NR activity and NO production. Important components of phytoglobin-NO cycle such as methaemoglobin reductase activity, expression of Phytoglobin1, NIA1 were elevated under anaerobic conditions in the presence of nitrite. The operation of phytoglobin-NO cycle also enhanced anaerobic ATP generation, LDH, ADH activities and in parallel ethylene levels were also enhanced. Interestingly nitrite suppressed the ROS production and lipid peroxidation. The reduction of ROS was accompanied by enhanced expression of mitochondrial alternative oxidase protein and its capacity. Application of AOX inhibitor SHAM inhibited the anoxic growth mediated by nitrite. In addition, nitrite improved the submergence tolerance of seedlings. Our study revealed that nitrite driven phytoglobin-NO cycle and AOX are crucial players in anaerobic germination and growth of deepwater rice.

Breeding Canola (Brassica napus L.) for Protein in Feed and Food

Interest in canola (Brassica napus L.). In response to this interest, scientists have been tasked with altering and optimizing the protein production chain to ensure canola proteins are safe for consumption and economical to produce. Specifically, the role of plant breeders in developing suitable varieties with the necessary protein profiles is crucial to this interdisciplinary endeavour. In this article, we aim to provide an overarching review of the canola protein chain from the perspective of a plant breeder, spanning from the genetic regulation of seed storage proteins in the crop to advancements of novel breeding technologies and their application in improving protein quality in canola. A review on the current uses of canola meal in animal husbandry is presented to underscore potential limitations for the consumption of canola meal in mammals. General discussions on the allergenic potential of canola proteins and the regulation of novel food products are provided to highlight some of the challenges that will be encountered on the road to commercialization and general acceptance of canola protein as a dietary protein source.

The metabolic environment of the developing embryo: A multidisciplinary approach on oilseed rapeseed

Brassicaceae seeds consist of three genetically distinct structures: the embryo, endosperm and seed coat, all of which are involved in assimilate allocation during seed development. The complexity of their metabolic interrelations remains unresolved to date. In the present study, we apply state-of-the-art imaging and analytical approaches to assess the metabolic environment of the Brassica napus embryo. Nuclear magnetic resonance imaging (MRI) provided volumetric data on the living embryo and endosperm, revealing how the endosperm envelops the embryo, determining endosperm's priority in assimilate uptake from the seed coat during early development. MRI analysis showed higher levels of sugars in the peripheral endosperm facing the seed coat, but a lower sugar content within the central vacuole and the region surrounding the embryo. Feeding intact siliques with ¹³C-labeled sucrose allowed tracing of the post-phloem route of sucrose transfer within the seed at the heart stage of embryogenesis, by means of mass spectrometry imaging. Quantification of over 70 organic and inorganic compounds in the endosperm revealed shifts in their abundance over different stages of development, while sugars and potassium were the main determinants of osmolality throughout these stages. Our multidisciplinary approach allows access to the hidden aspects of endosperm metabolism, a task which remains unattainable for the small-seeded model plant Arabidopsis thaliana.

Temporal changes in metabolism late in seed development affect biomass composition

The negative association between protein and oil production in soybean (Glycine max) seed is well-documented. However, this inverse relationship is based primarily on the composition of mature seed, which reflects the cumulative result of events over the course of soybean seed development and therefore does not convey information specific to metabolic fluctuations during developmental growth regimes. In this study, we assessed maternal nutrient supply via measurement of seed coat exudates and metabolite levels within the cotyledon throughout development to identify trends in the accumulation of central carbon and nitrogen metabolic intermediates. Active metabolic activity during late seed development was probed through transient labeling with 13C substrates. The results indicated: (1) a drop in lipid contents during seed maturation with a concomitant increase in carbohydrates, (2) a transition from seed filling to maturation phases characterized by quantitatively balanced changes in carbon use and CO2 release, (3) changes in measured carbon and nitrogen resources supplied maternally throughout development, (4) 13C metabolite production through gluconeogenic steps for sustained carbohydrate accumulation as the maternal nutrient supply diminishes, and (5) oligosaccharide biosynthesis within the seed coat during the maturation phase. These results highlight temporal engineering targets for altering final biomass composition to increase the value of soybeans and a path to breaking the inverse correlation between seed protein and oil content.

CRISPR/Cas9-Induced fad2 and rod1 Mutations Stacked With fae1 Confer High Oleic Acid Seed Oil in Pennycress (Thlaspi arvense L.)

Pennycress (Thlaspi arvense L.) is being domesticated as an oilseed cash cover crop to be grown in the off-season throughout temperate regions of the world. With its diploid genome and ease of directed mutagenesis using molecular approaches, pennycress seed oil composition can be rapidly tailored for a plethora of food, feed, oleochemical and fuel uses. Here, we utilized Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 technology to produce knockout mutations in the FATTY ACID DESATURASE2 (FAD2) and REDUCED OLEATE DESATURATION1 (ROD1) genes to increase oleic acid content. High oleic acid (18:1) oil is valued for its oxidative stability that is superior to the polyunsaturated fatty acids (PUFAs) linoleic (18:2) and linolenic (18:3), and better cold flow properties than the very long chain fatty acid (VLCFA) erucic (22:1). When combined with a FATTY ACID ELONGATION1 (fae1) knockout mutation, fad2 fae1 and rod1 fae1 double mutants produced ∼90% and ∼60% oleic acid in seed oil, respectively, with PUFAs in fad2 fae1 as well as fad2 single mutants reduced to less than 5%. MALDI-MS spatial imaging analyses of phosphatidylcholine (PC) and triacylglycerol (TAG) molecular species in wild-type pennycress embryo sections from mature seeds revealed that erucic acid is highly enriched in cotyledons which serve as storage organs, suggestive of a role in providing energy for the germinating seedling. In contrast, PUFA-containing TAGs are enriched in the embryonic axis, which may be utilized for cellular membrane expansion during seed germination and seedling emergence. Under standard growth chamber conditions, rod1 fae1 plants grew like wild type whereas fad2 single and fad2 fae1 double mutant plants exhibited delayed growth and overall reduced heights and seed yields, suggesting that reducing PUFAs below a threshold in pennycress had negative physiological effects. Taken together, our results suggest that combinatorial knockout of ROD1 and FAE1 may be a viable route to commercially increase oleic acid content in pennycress seed oil whereas mutations in FAD2 will likely require at least partial function to avoid fitness trade-offs.

Analyzing Mass Spectrometry Imaging Data of 13C-Labeled Phospholipids in Camelina sativa and Thlaspi arvense (Pennycress) Embryos

The combination of ¹³C-isotopic labeling and mass spectrometry imaging (MSI) offers an approach to analyze metabolic flux in situ. However, combining isotopic labeling and MSI presents technical challenges ranging from sample preparation, label incorporation, data collection, and analysis. Isotopic labeling and MSI individually create large, complex data sets, and this is compounded when both methods are combined. Therefore, analyzing isotopically labeled MSI data requires streamlined procedures to support biologically meaningful interpretations. Using currently available software and techniques, here we describe a workflow to analyze ¹³C-labeled isotopologues of the membrane lipid and storage oil lipid intermediate―phosphatidylcholine (PC). Our results with embryos of the oilseed crops, Camelina sativa and Thlaspi arvense (pennycress), demonstrated greater ¹³C-isotopic labeling in the cotyledons of developing embryos compared with the embryonic axis. Greater isotopic enrichment in PC molecular species with more saturated and longer chain fatty acids suggest different flux patterns related to fatty acid desaturation and elongation pathways. The ability to evaluate MSI data of isotopically labeled plant embryos will facilitate the potential to investigate spatial aspects of metabolic flux in situ.

Developmental and genomic architecture of plant embryogenesis: from model plant to crops

Embryonic development represents an important reproductive phase of sexually reproducing plant species. The fusion of egg and sperm produces the plant zygote, a totipotent cell that, through cell division and cell identity specification in early embryogenesis, establishes the major cell lineages and tissues of the adult plant. The subsequent morphogenesis phase produces the full-sized embryo, while the late embryogenesis maturation process prepares the seed for dormancy and subsequent germination, ensuring continuation of the plant life cycle. In this review on embryogenesis, we compare the model eudicot Arabidopsis thaliana with monocot crops, focusing on genome activation, paternal and maternal regulation of early zygote development, and key organizers of patterning, such as auxin and WOX transcription factors. While the early stages of embryo development are apparently conserved among plant species, embryo maturation programs have diversified between eudicots and monocots. This diversification in crop species reflects the likely effects of domestication on seed quality traits that are determined during embryo maturation, and also assures seed germination in different environmental conditions. This review describes the most important features of embryonic development in plants, and the scope and applications of genomics in plant embryo studies.

The NAC Transcription Factors OsNAC20 and OsNAC26 Regulate Starch and Storage Protein Synthesis

Starch and storage proteins determine the weight and quality of cereal grains. Synthesis of these two grain components has been comprehensively investigated, but the transcription factors responsible for their regulation remain largely unknown. In this study, we investigated the roles of NAM, ATAF, and CUC (NAC) transcription factors, OsNAC20, and OsNAC26 in starch and storage protein synthesis in rice (Oryza sativa) endosperm. OsNAC20 and OsNAC26 showed high levels of amino acid sequence similarity. Both were localized in the aleurone layer, starchy endosperm, and embryo. Mutation of OsNAC20 or OsNAC26 alone had no effect on the grain, while the osnac20/26 double mutant had significantly decreased starch and storage protein content. OsNAC20 and OsNAC26 alone could directly transactivate the expression of starch synthaseI (SSI), pullulanase (Pul), glutelin A1 (GluA1), glutelin B4/5 (GluB4/5), α-globulin, and 16 kD prolamin and indirectly influenced plastidial disproportionating enzyme1 (DPE1) expression to regulate starch and storage protein synthesis. Although they could also bind to the promoters of ADP-Glc pyrophosphorylase small subunit 2b (AGPS2b), ADP-Glc pyrophosphorylase large subunit 2 (AGPL2), and starch branching enzymeI (SBEI), and the expression of the three genes was largely decreased in the osnac20/26 mutant, ADP-Glc pyrophosphorylase and starch branching enzyme activities were unchanged in this double mutant. In addition, OsNAC20 and OsNAC26 are main regulators of Pul, GluB4, α-globulin, and 16 kD prolamin In conclusion, OsNAC20 and OsNAC26 play an essential and redundant role in the regulation of starch and storage protein synthesis.