Improvement in the quality of seed storage protein by transformation of Brassica napus with an antisense gene for cruciferin

Genomic Regions Associated With Seed Meal Quality Traits in Brassica napus Germplasm

The defatted Brassica napus (rapeseed) meal can be high-protein feed for livestock as the protein value of rapeseed meal is higher than that of the majority of other vegetable proteins. Extensive work has already been carried out on developing canola rapeseed where the focus was on reducing erucic acid and glucosinolate content, with less consideration to other antinutritional factors such as tannin, phytate, sinapine, crude fiber, etc. The presence of these antinutrients limits the use and marketing of rapeseed meals and a significant amount of it goes unused and ends up as waste. We investigated the genetic architecture of crude protein, methionine, tryptophan, total phenols, β-carotene, glucosinolates (GLSs), phytate, tannins, sinapine, and crude fiber content of defatted seed meal samples by conducting a genome-wide association study (GWAS), using a diversity panel comprising 96 B. napus genotypes. Genotyping by sequencing was used to identify 77,889 SNPs, spread over 19 chromosomes. Genetic diversity and phenotypic variations were generally high for the studied traits. A total of eleven genotypes were identified which showed high-quality protein, high antioxidants, and lower amount of antinutrients. A significant negative correlation between protein and limiting amino acids and a significant positive correlation between GLS and phytic acid were observed. General and mixed linear models were used to estimate the association between the SNP markers and the seed quality traits and quantile-quantile (QQ) plots were generated to allow the best-fit algorithm. Annotation of genomic regions around associated SNPs helped to predict various trait-related candidates such as ASP2 and EMB1027 (amino acid biosynthesis); HEMA2, GLU1, and PGM (tryptophan biosynthesis); MS3, CYSD1, and MTO1 (methionine biosynthesis); LYC (β-carotene biosynthesis); HDR and ISPF (MEP pathway); COS1 (riboflavin synthesis); UGT (phenolics biosynthesis); NAC073 (cellulose and hemicellulose biosynthesis); CYT1 (cellulose biosynthesis); BGLU45 and BGLU46 (lignin biosynthesis); SOT12 and UGT88A1 (flavonoid pathway); and CYP79A2, DIN2, and GSTT2 (GLS metabolism), etc. The functional validation of these candidate genes could confirm key seed meal quality genes for germplasm enhancement programs directed at improving protein quality and reducing the antinutritional components in B. napus.

Engineering a feedback inhibition-insensitive plant dihydrodipicolinate synthase to increase lysine content in Camelina sativa seeds

Camelina sativa (camelina) is emerging as an alternative oilseed crop due to its short growing cycle, low input requirements, adaptability to less favorable growing environments and a seed oil profile suitable for biofuel and industrial applications. Camelina meal and oil are also registered for use in animal and fish feeds; however, like meals derived from most cereals and oilseeds, it is deficient in certain essential amino acids, such as lysine. In higher plants, the reaction catalyzed by dihydrodipicolinate synthase (DHDPS) is the first committed step in the biosynthesis of lysine and is subject to regulation by lysine through feedback inhibition. Here, we report enhancement of lysine content in C. sativa seed via expression of a feedback inhibition-insensitive form of DHDPS from Corynebacterium glutamicums (CgDHDPS). Two genes encoding C. sativa DHDPS were identified and the endogenous enzyme is partially insensitive to lysine inhibition. Site-directed mutagenesis was used to examine the impact of alterations, alone and in combination, present in lysine-desensitized DHDPS isoforms from Arabidopsis thaliana DHDPS (W53R), Nicotiana tabacum (N80I) and Zea mays (E84K) on C. sativa DHDPS lysine sensitivity. When introduced alone, each of the alterations decreased sensitivity to lysine; however, enzyme specific activity was also affected. There was evidence of molecular or structural interplay between residues within the C. sativa DHDPS allosteric site as coupling of the W53R mutation with the N80V mutation decreased lysine sensitivity of the latter, but not to the level with the W53R mutation alone. Furthermore, the activity and lysine sensitivity of the triple mutant (W53R/N80V/E84T) was similar to the W53R mutation alone or the C. glutamicum DHDPS. The most active and most lysine-insensitive C. sativa DHDPS variant (W53R) was not inhibited by free lysine up to 1 mM, comparable to the C. glutamicums enzyme. Seed lysine content increased 13.6 -22.6% in CgDHDPS transgenic lines and 7.6–13.2% in the mCsDHDPS lines. The high lysine-accumulating lines from this work may be used to produce superior quality animal feed with improved essential amino acid profile.

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.

Genetic and Molecular Regulation of Seed Storage Proteins (SSPs) to Improve Protein Nutritional Value of Oilseed Rape (Brassica napus L.) Seeds

The world-wide demand for additional protein sources for human nutrition and animal feed keeps rising due to rapidly growing world population. Oilseed rape is a second important oil producing crop and the by-product of the oil production is a protein rich meal. The protein in rapeseed meal finds its application in animal feed and various industrial purposes, but its improvement is of great interest, especially for non-ruminants and poultry feed. To be able to manipulate the quality and quantity of seed protein in oilseed rape, understanding genetic architecture of seed storage protein (SSPs) synthesis and accumulation in this crop species is of great interest. For this, application of modern molecular breeding tools such as whole genome sequencing, genotyping, association mapping, and genome editing methods implemented in oilseed rape seed protein improvement would be of great interest. This review examines current knowledge and opportunities to manipulate of SSPs in oilseed rape to improve its quality, quantity and digestibility.

Engineering sulfur storage in maize seed proteins without apparent yield loss

Sulfur assimilation may limit the pool of methionine and cysteine available for incorporation into zeins, the major seed storage proteins in maize. This hypothesis was tested by producing transgenic maize with deregulated sulfate reduction capacity achieved through leaf-specific expression of the Escherichia coli enzyme 3'-phosphoadenosine-5'-phosphosulfate reductase (EcPAPR) that resulted in higher methionine accumulation in seeds. The transgenic kernels have higher expression of the methionine-rich 10-kDa δ-zein and total protein sulfur without reduction of other zeins. This overall increase in the expression of the S-rich zeins describes a facet of regulation of these proteins under enhanced sulfur assimilation. Transgenic line PE5 accumulates 57.6% more kernel methionine than the high-methionine inbred line B101. In feeding trials with chicks, PE5 maize promotes significant weight gain compared with nontransgenic kernels. Therefore, increased source strength can improve the nutritional value of maize without apparent yield loss and may significantly reduce the cost of feed supplementation.

Targeted modification of storage protein content resulting in improved amino acid composition of barley grain

C-hordein in barley and ω-gliadins in wheat are members of the prolamins protein families. Prolamins are the major component of cereal storage proteins and composed of non-essential amino acids (AA) such as proline and glutamine therefore have low nutritional value. Using double stranded RNAi silencing technology directed towards C-hordein we obtained transgenic barley lines with up to 94.7% reduction in the levels of C-hordein protein relative to the parental line. The composition of the prolamin fraction of the barley parental line cv. Golden Promise was resolved using SDS-PAGE electrophoresis, the protein band were excised and the proteins identified by quadrupole-time-of-flight mass spectrometry. Subsequent SDS-PAGE separation and analysis of the prolamin fraction of the transgenic lines revealed a reduction in the amounts of C-hordeins and increases in the content of other hordein family members. Analysis of the AA composition of the transgenic lines showed that the level of essential amino acids increased with a concomitant reduction in proline and glutamine. Both the barley C-hordein and wheat ω-gliadin genes proved successful for RNAi-gene mediated suppression of barley C-hordein level. All transgenic lines that exhibited a reduction for C-hordein showed off-target effects: the lines exhibited increased level of B/γ-hordein while D-hordein level was reduced. Furthermore, the multicopy insertions correlated negatively with silencing.

Heat stress during seed filling interferes with sulfur restriction on grain composition and seed germination in oilseed rape (Brassica napus L.)

In coming decades, increasing temperatures are expected to impact crop yield and seed quality. To develop low input systems, the effects of temperature and sulfur (S) nutrition in oilseed rape, a high S demanding crop, need to be jointly considered. In this study, we investigated the effects of temperatures [High Temperature (HT), 33°C/day, 19°C/night vs. Control Temperature (Ctrl T), 20°C/day, 15°C/day] and S supply [High S (HS), 500 μm SO(2-) 4 vs. Low S (LS), 8.7 μM SO(2-) 4] during seed filling on (i) yield components [seed number, seed dry weight (SDW) and seed yield], (ii) grain composition [nitrogen (N) and S contents] and quality [fatty acid (FA) composition and seed storage protein (SSP) accumulation] and (iii) germination characteristics (pre-harvest sprouting, germination rates and abnormal seedlings). Abscisic acid (ABA), soluble sugar contents and seed conductivity were also measured. HT and LS decreased the number of seeds per plant. SDW was less affected due to compensatory effects since the number of seeds decreased under stress conditions. While LS had negative effects on seed composition by reducing the FA contents and increasing the ratio S-poor SSPs (12S globulins)/S-rich SSPs (2S albumins) ratio, HT had positive effects by increasing S and FA contents and decreasing the C18:2/C18:3 ratio and the 12S/2S protein ratio. Seeds produced under HT showed high pre-harvest sprouting rates along with decreased ABA contents and high rates of abnormal seedlings. HT and LS restriction significantly accelerated germination times. High conductivity, which indicates poor seed storage capacity, was higher in HT seeds. Consistently, the lower ratio of (raffinose + stachyose)/sucrose in HT seeds indicated low seed storage capacity. We demonstrated the effects of HT and LS on grain and on germination characteristics. These results suggest that hormonal changes might control several seed characteristics simultaneously.

Mapping of QTL for the seed storage proteins cruciferin and napin in a winter oilseed rape doubled haploid population and their inheritance in relation to other seed traits

Cruciferin (cru) and napin (nap) were negatively correlated and the cru/nap ratio was closely negative correlated with glucosinolate content indicating a link between the two biosynthetic pathways. Canola-type oilseed rape (Brassica napus L.) is an economically important oilseed crop in temperate zones. Apart from the oil, the canola protein shows potential as a value-added food and nutraceutical ingredient. The two major storage protein groups occurring in oilseed rape are the 2 S napins and 12 S cruciferins. The aim of the present study was to analyse the genetic variation and the inheritance of napin and cruciferin content of the seed protein in the winter oilseed rape doubled haploid population Express 617 × R53 and to determine correlations to other seed traits. Seed samples were obtained from field experiments performed in 2 years at two locations with two replicates in Germany. A previously developed molecular marker map of the DH population was used to map quantitative trait loci (QTL) of the relevant traits. The results indicated highly significant effects of the year and the genotype on napin and cruciferin content as well as on the ratio of cruciferin to napin. Heritabilities were comparatively high with 0.79 for napin and 0.77 for cruciferin. Napin and cruciferin showed a significant negative correlation (-0.36**) and a close negative correlation of the cru/nap ratio to glucosinolate content was observed (-0.81**). Three QTL for napin and two QTL for cruciferin were detected, together explaining 47 and 35 % of the phenotypic variance. A major QTL for glucosinolate content was detected on linkage group N19 whose confidence interval overlapped with QTL for napin and cruciferin content. Results indicate a relationship between seed protein composition and glucosinolate content.

A strategy for targeting recombinant proteins to protein storage vacuoles by fusion to Brassica napus napin in napin-depleted seeds

Seeds are capable of accumulating high levels of seed storage proteins (SSP), as well as heterologous proteins under certain conditions. Arabidopsis thaliana was used to develop a strategy to deplete seeds of an endogenous SSP and then replenish them with the same protein fused to a heterologous protein. In several other studies, competition with endogenous SSP for space and metabolic resources was shown to affect the accumulation of recombinant proteins in seeds. We used RNAi to reduce the expression of the five napin genes and deplete the seeds of this SSP. Targeting a recombinant protein to a vacuole or structure within the seed where it can be protected from cytosolic proteases can also promote its accumulation. To achieve this, a synthetic Brassica napus napin gene (Bn napin) was designed that was both impervious to the A. thaliana napin (At napin) RNAi construct and permitted fusion to a heterologous protein, in this case green fluorescent protein (GFP). GFP was placed in several strategic locations within Bn napin with consideration to maintaining structure, processing sites and possible vacuolar targeting signals. In transgenic A. thaliana plants, GFP was strongly localized to the seed protein storage vacuole in all Bn napin fusion configurations tested, but not when expressed alone. This SSP depletion-replenishment strategy outlined here would be applicable to expression of recombinant proteins in industrial crops that generally have large repertoires of endogenous SSP genes.

Next-generation protein-rich potato expressing the seed protein gene AmA1 is a result of proteome rebalancing in transgenic tuber

Protein deficiency is the most crucial factor that affects physical growth and development and that increases morbidity and mortality especially in developing countries. Efforts have been made to improve protein quality and quantity in crop plants but with limited success. Here, we report the development of transgenic potatoes with enhanced nutritive value by tuber-specific expression of a seed protein, AmA1 (Amaranth Albumin 1), in seven genotypic backgrounds suitable for cultivation in different agro-climatic regions. Analyses of the transgenic tubers revealed up to 60% increase in total protein content. In addition, the concentrations of several essential amino acids were increased significantly in transgenic tubers, which are otherwise limited in potato. Moreover, the transgenics also exhibited enhanced photosynthetic activity with a concomitant increase in total biomass. These results are striking because this genetic manipulation also resulted in a moderate increase in tuber yield. The comparative protein profiling suggests that the proteome rebalancing might cause increased protein content in transgenic tubers. Furthermore, the data on field performance and safety evaluation indicate that the transgenic potatoes are suitable for commercial cultivation. In vitro and in vivo studies on experimental animals demonstrate that the transgenic tubers are also safe for human consumption. Altogether, these results emphasize that the expression of AmA1 is a potential strategy for the nutritional improvement of food crops.

Recovery of transgenic plants by pollen-mediated transformation in Brassica juncea

The aroA-M1 encoding the mutant of 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS) was introduced into the Brassica juncea genome by sonication-assisted, pollen-mediated transformation. The plasmid DNA and collected pollen grains were mixed in 0.3 mol/L sucrose solution and treated with mild ultrasonication. The treated pollen was then pollinated onto the oilseed stigmas after the stamens were removed artificially. Putative transgenic plants were obtained by screening germinating seeds on a medium containing glyphosate. Southern blot analysis of glyphosate-resistant plants indicated that the aroA-M1 gene had been integrated into the oilseed genome. Western blot analysis further confirmed that the EPSPS coded by aroA-M1 gene was expressed in transgenic plants. The transgenic plants exhibited increased resistance to glyphosate compared to untransformed plants. Some of those transgenic plants had considerably high resistance to glyphosate. The genetic analysis of T1 progeny further confirmed that the inheritance of the introduced genes followed the Mendelian rules. The results indicated that foreign genes can be transferred by pollen-mediated transformation combined with mild ultrasonication.

Antisense expression of 3-oxoacyl-ACP reductase affects whole plant productivity and causes collateral changes in activity of fatty acid synthase components

Brassica napus cv Westar plants were transformed with 3-oxoacyl-ACP reductase (KR) in antisense orientation, driven by either the cauliflower mosaic virus 35S promoter or a seed-specific acyl carrier protein promoter to determine the effects on plant productivity and on the activity of other fatty acid synthase (FAS) components. In plants with altered KR activity, total seed yield was reduced in all cases. In less severely affected plant lines, seeds had a normal appearance and composition but the yield of seeds was reduced by approximately 50%. In more severely affected lines, reductions in both seed fatty acid content and the number of seeds produced per plant were evident, resulting in a 90% reduction in fatty acid synthesized per plant. These phenotypes were independent of the promoter used. In severely affected lines, a large proportion of seeds showed precocious germination, and these had a reduced oleate content and increased levels of polyunsaturated 18-carbon fatty acids, compared with normal seeds of the same line. This reduction in 18:1 fatty acids was mimicked on imbibition of seeds with a normal appearance, indicating a preferential use of oleate moieties in precocious germination events. The reduction in activity of KR was mirrored for a second fatty acid synthase component, enoyl-ACP reductase, indicating a mechanism to maintain the ratio of fatty acid synthase components throughout embryogenesis.

Effects of protein engineering of canola procruciferin on its physicochemical and functional properties

The primary structure of Brassica napus procruciferin 2/3a was engineered to elucidate structure-function relationships and to improve the functionality of cruciferin. The following mutants were constructed: (1) C287T, (2) DeltaII, variable region II was deleted; (3) C287T/DeltaII, mutation involving (1) and (2); (4) DeltaIV + A1aIV; and (5) DeltaIV + A3IV, variable region IV was replaced with variable region IV containing many charged residues from soybean glycinin A1aB1b and A3B4 subunits. Differential scanning calorimetry analysis revealed that the A1aIV region has a more favorable interaction with the procruciferin molecule than does A3IV as well as the original regions. On the basis of heat-induced precipitation analysis, it was concluded that replacement of the free cysteine residue with threonine (C287T) and insertion of charged regions (DeltaIV + A1aIV and DeltaIV + A3IV) could lead procruciferin to form soluble aggregates after heating. Low solubility was observed in mutants DeltaIV + A3IV, DeltaII, and C287T/DeltaII, especially between pH 4 and 6 at mu = 0.08, but not in DeltaIV + A1aIV, indicating that the number of acidic amino acid residues and the high number of glutamine residues are important factors for solubility at mu = 0.08. None of the mutants showed any improvements in emulsifying ability, indicating that destabilization and addition of the hydrophilic region are not effective for emulsification. The insertion of the A1aIV region in procruciferin made the molecule more susceptible to alpha-chymotrypsin.

Transgenic carrots with enhanced resistance against two major pathogens, Erysiphe heraclei and Alternaria dauci

In vitro assay indicated that the human lysozyme has lytic activity against phytopathogenic fungi and bacteria. A human lysozyme gene was placed under control of the constitutive CaMV 35S promoter and the resulting expression plasmid was introduced into two cultivars (cv.) of carrot, Kurodagosun (K5) and Nantes Scarlet (NS), by Agrobacterium tumefaciens-mediated method. Seven and fourteen transgenic plants of cv. K5 and cv. NS were regenerated, respectively, and the obtained transgenic carrots of T0 generation was tested for disease resistance against Erysiphe heraclei, a pathogenic fungi causing powdery mildew. Among the tested lines, the transgenic plant No. 12-1 and 8-1 of cv. NS showed a fairly strong resistance against E. heraclei. The strong disease resistance was also confirmed in T1 generation. Disease resistance against another pathogen of leaf blight, Alternaria dauci, were also tested using T1 transgenic lines. Significant enhanced resistance was observed in the No. 12-1 of cv. NS. Accumulation of synthesized human lysozyme protein was observed in this line, a finding consistent with observed disease resistance.

Co-introduction of an antisense gene for an endogenous seed storage protein can increase expression of a transgene in Arabidopsis thaliana seeds

We have investigated whether the expression in Arabidopsis thaliana seeds of a transgene (the Phaseolus vulgaris arcelin (arc)5-I gene) could be enhanced by the simultaneous introduction of an antisense gene for an endogenous seed storage protein (2S albumin). Seeds of plants transformed with both the arc5-I gene and a 2S albumin antisense gene contained reduced amounts of 2S albumins and increased arcelin-5 (Arc5) accumulation levels compared to lines harboring the arc5-I gene only. Arc5 production could be enhanced to more than 24% of the total seed protein content, suggesting that antisense technology could be of great utility to favor high expression of transgenes.