Rice Lipid Research Articles

Evaluating rice lipid content, yield, and quality in response to nitrogen application rate and planting density.

To investigate the effects of nitrogen (N) application rate and planting density (D) on the contents of lipid and free fatty acid, fatty acid composition, yield and quality of rice grain, a field experiment was conducted using Koshihikari (japonica) as experimental material from 2021 to 2022 with three N levels (90, 150 and 210 kg ha-1, denoted as N1, N2 and N3, respectively) and three transplanting densities (19.0 × 104, 26.7 × 104 and 40.0 × 104 plants ha-1, denoted as D1, D2 and D3, respectively). The results showed that N application rate and planting density had highly significant impacts only on the contents of free fatty acid and saturated fatty acid, respectively. Increased N and planting density enhanced the contents of lipid (29.41 mg g-1) and free fatty acid (21.47%). The highest values were obtained under N3D3 increasing by 7.02% and 3.23 percentage points, respectively, compared to other treatments. No significant differences in lipid content were found among treatments, whereas free fatty acid exhibited significant differences. The unsaturated fatty acid content increased with increasing N but first decreased and then increased with increasing planting density, while saturated fatty acid content showed the opposite trend. Appropriate N level and planting density improved the relative chlorophyll content and net photosynthetic rate of rice flag leaves, as well as increased grain yield, effective panicle number and spikelete number per panicle, but decreased the seed setting rate. Under N2D2, the relative chlorophyll content and net photosynthetic rate remained relatively high throughout the grain filling stage, resulting in the highest grain yield, with increases of 43.87-47.03% compared to other treatments. Amoderate N level improved the milling quality of rice, while increased planting density reduced it. However, both increased N and planting density reduced the appearance quality and cooking and eating quality of rice. Overall, the effects of increasing N application rate and planting density on enhancing rice lipid and free fatty acid contents were limited. A combination of 150 kg ha-1 N application rate and 26.7 × 104 plants ha-1 was recommended for achieving relatively higher yield, lipid content and better grain quality.

Biological Roles of Lipids in Rice.

Lipids are organic nonpolar molecules with essential biological and economic importance. While the genetic pathways and regulatory networks of lipid biosynthesis and metabolism have been extensively studied and thoroughly reviewed in oil crops such as soybeans, less attention has been paid to the biological roles of lipids in rice, a staple food for the global population and a model species for plant molecular biology research, leaving a considerable knowledge gap in the biological roles of lipids. In this review, we endeavor to furnish a current overview of the advancements in understanding the genetic foundations and physiological functions of lipids, including triacylglycerol, fatty acids, and very-long-chain fatty acids. We aim to summarize the key genes in lipid biosynthesis, metabolism, and transcriptional regulation underpinning rice's developmental and growth processes, biotic stress responses, abiotic stress responses, fertility, seed longevity, and recent efforts in rice oil genetic improvement.

Lipidomics and volatilomics reveal the changes in lipids and their volatile oxidative degradation products of brown rice during accelerated aging.

Brown rice exhibits higher nutritional value and attracts more and more attentions; however, lipid alteration in brown rice during aging is poorly understood. In this study, lipidomics and volatilomics were employed to investigate free fatty acids, triglycerides, and volatile oxidative degradation products of lipids in brown rice during accelerated aging for 70days. The results showed that the total free fatty acids in brown rice increased significantly (2.90-4.14 times) while triglycerides decreased remarkably at the initial stage of aging. Monounsaturated and polyunsaturated aldehydes, ketones, and acids increased obviously in brown rice during accelerated aging for 70days. The screening of significantly different compounds indicated that the enzymatic hydrolysis of triglycerides (EHT) and enzymatic oxidation of lipids (EOL) were the main biochemical behaviors at the initial stage of aging (0-28day) while automatic oxidation of lipids (AOL) was the primary chemical reaction for 28-70days aging.

Impacts of Inherent Components and Nitrogen Fertilizer on Eating and Cooking Quality of Rice: A Review.

With the continuous improvement of living standards, the preferences of consumers are shifting to rice varieties with high eating and cooking quality (ECQ). Milled rice is mainly composed of starch, protein, and oil, which constitute the physicochemical basis of rice taste quality. This review summarizes the relationship between rice ECQ and its intrinsic ingredients, and also briefly introduces the effects of nitrogen fertilizer management on rice ECQ. Rice varieties with higher AC usually have more long branches of amylopectin, which leach less when cooking, leading to higher hardness, lower stickinesss, and less panelist preference. High PC impedes starch pasting, and it may be hard for heat and moisture to enter the rice interior, ultimately resulting in worse rice eating quality. Rice with higher lipid content had a brighter luster and better eating quality, and starch lipids in rice have a greater impact on rice eating quality than non-starch lipids. The application of nitrogen fertilizer can enhance rice yield, but it also decreases the ECQ of rice. CRNF has been widely used in cereal crops such as maize, wheat, and rice as a novel, environmentally friendly, and effective fertilizer, and could increase rice quality to a certain extent compared with conventional urea. This review shows a benefit to finding more reasonable nitrogen fertilizer management that can be used to regulate the physical and chemical indicators of rice grains in production and to improve the taste quality of rice without affecting yield.

Improved bioenergy value of residual rice straw by increased lipid levels from upregulation of fatty acid biosynthesis

BackgroundRice (Oryza sativa) straw is a common waste product that represents a considerable amount of bound energy. This energy can be used for biogas production, but the rate and level of methane produced from rice straw is still low. To investigate the potential for an increased biogas production from rice straw, we have here utilized WRINKLED1 (WRI1), a plant AP2/ERF transcription factor, to increase triacylglycerol (TAG) biosynthesis in rice plants. Two forms of Arabidopsis thaliana WRI1 were evaluated by transient expression and stable transformation of rice plants, and transgenic plants were analyzed both for TAG levels and biogas production from straw.ResultsBoth full-length AtWRI1, and a truncated form lacking the initial 141 amino acids (including the N-terminal AP2 domain), increased fatty acid and TAG levels in vegetative and reproductive tissues of Indica rice. The stimulatory effect of the truncated AtWRI1 was significantly lower than that of the full-length protein, suggesting a role for the deleted AP2 domain in WRI1 activity. Full-length AtWRI1 increased TAG levels also in Japonica rice, indicating a conserved effect of WRI1 in rice lipid biosynthesis. The bio-methane production from rice straw was 20% higher in transformants than in the wild type. Moreover, a higher producing rate and final yield of methane was obtained for rice straw compared with rice husks, suggesting positive links between methane production and a high amount of fatty acids.ConclusionsOur results suggest that heterologous WRI1 expression in transgenic plants can be used to improve the metabolic potential for bioenergy purposes, in particular methane production.

Rice lipid transfer protein, OsLTPL23, controls seed germination by regulating starch-sugar conversion and ABA homeostasis.

Seed germination is vital for ensuring the continuity of life in spermatophyte. High-quality seed germination usually represents good seedling establishment and plant production. Here, we identified OsLTPL23, a putative rice non-specific lipid transport protein, as an important regulator responsible for seed germination. Subcellular localization analysis confirmed that OsLTPL23 is present in the plasma membrane and nucleus. The knockout mutants of OsLTPL23 were generated by CRISPR/Cas9-mediated genome editing, and osltpl23 lines significantly germinated slower and lower than the Nipponbare (NIP). Starch and soluble sugar contents measurement showed that OsLTPL23 may have alpha-amylase inhibitor activity, and high soluble sugar content may be a causal agent for the delayed seed germination of osltpl23 mutants. Transcript profiles in the germinating seeds exhibited that the abscisic acid (ABA)-responsive genes, OsABI3 and OsABI5, and biosynthesis genes, OsNCED1, OsNCED2, OsNCED3 and OsNCED4, are obviously upregulated in the osltpl23 mutants compared to NIP plants, conversely, ABA metabolism genes OsABA8ox1, OsABA8ox2 and OsABA8ox3 are stepwise decreased. Further investigations found that osltpl23 mutants displays weakened early seedling growth, with elevated gene expresssion of ABA catabolism genes and repressive transcription response of defence-related genes OsWRKY45, OsEiN3, OsPR1a, OsPR1b and OsNPR1. Integrated analysis indicated that OsLTPL23 may exert an favorable effect on rice seed germination and early seedling growth via modulating endogenous ABA homeostasis. Collectively, our study provides important insights into the roles of OsLTPL23-mediated carbohydrate conversion and endogenous ABA pathway on seed germination and early seedling growth, which contributes to high-vigor seed production in rice breeding.

A reliable and effective sample preparation protocol of MALDI-TOF-MSI for lipids imaging analysis in hard and dry cereals

A superior sectioning sample preparation protocol is the basic guarantee for maintaining data reliability in MALDI-TOF-MSI analysis. Despite significant advances in sample preparation, visualization of lipids in hard and dry cereals remains difficult due to their inherent physicochemical properties. Thus, a cryosections preparation method was designed via poly-l-lysine soaking, conductive tape adhesion and embedding medium fixation, which preserved the spatial integrity of lipids in cereals without causing analyte delocalization and obvious background interference. Higher signal intensity and clearer imaging of lipids in rice, wheat and barley (Qingke) were obtained using the established sample preparation method. Moreover, the spatial distribution of lipids was visualized in rice with different storage years, which found that the phosphatidylinositols (PIs) and phosphatidylglycerols (PGs) could be used for evaluation of rice aging degree. Our study provided molecular level guidance for further discussion of rice aging mechanism, rice quality evaluation and safety monitoring.

QFC6, a major gene for crude fat content and quality in rice

qFC6, a major quantitative trait locus for rice crude fat content, was fine mapped to be identical with Wx. FC6 negatively regulates crude fat content and rice quality. Starch, protein and lipids are the three major components in rice endosperm. The lipids content in rice influences both storage and quality. In this study, we identified a quantitative trait locus (QTL), qFC6, for crude fat (free lipids) content through association analysis and linkage analysis. Gene-based association analysis revealed that LOC_Os06g04200, also known as Wx, was the candidate gene for qFC6. Complementation and knockout transgenic lines revealed that Wx negatively regulates crude fat content. Lipid composition and content analysis by gas chromatography and taste evaluation analysis showed that FC6 positively influenced bound lipids content and negatively affected both free lipids content and taste. Besides, higher free lipids content rice varieties exhibit more lustrous appearance after cooking and by adding extra oil during cooking could improve rice luster and taste score, indicating that higher free lipids content may make rice more lustrous and delicious. Together, we cloned a QTL coordinating rice crude fat content and eating quality and assisted in uncovering the genetic basis of rice lipid content and in the improvement of rice eating quality.

The Impact of Rice Lipid on In Vitro Rice Starch Digestibility.

The negative role of lipids in rice starch digestion is well-known; however, the effect of individual native lipids on starch digestibility has not been studied. In this study, native rice lipids, such as triacylglycerols (TAGs), diacylglycerols (DAGs), phosphatidylcholines (PCs) and lysophospholipids (LPLs), were analyzed using liquid chromatography–mass spectrometry (LC-MS) and correlated with in vitro rice starch digestibility. Most of the tested lipids exhibited a negative correlation with the in vitro starch digestibility with the correlations being more pronounced for LPLs. Removal of lipids from rice flour increased the in vitro starch digestibility. Conversely, a lipid extract addition to rice flour reduced the starch digestibility. Addition of 1% pure lysophosphatidylcholine (LPC)16:0, TAG54:6, DAG36:4 or PC36:2 individually to rice flour reduced starch digestibility by different extents in the order of LPC16:0 > TAG54:6 > PC36:2 > DAG36:4. LPC16:0 was the most abundant lipid among all the assessed lipids in the white rice (milled rice), and addition of 1% LPC 16:0 to rice flour reduced glucose release following three hours of in vitro starch digestion by 7.4%. There may be a scope to breed rice with a lipid composition to reach a desired starch digestibility or simply through addition of certain lipids before cooking the rice.

Polyploidization Increases the Lipid Content and Improves the Nutritional Quality of Rice.

Plant polyploidization is frequently associated with changes in nutrient contents. However, the possible contribution of metabolites to this change has not been investigated by characterizing the metabolite contents of diploid and tetraploid forms of rice (Oryza sativa L.). We compared the metabolites of a group of diploid–tetraploid japonica brown rice and a group of diploid–tetraploid indica brown rice based on liquid chromatography–tandem mass spectrometry. In total, 401 metabolites were identified; of these, between the two diploid–tetraploid groups, 180 showed opposite expression trends, but 221 showed the same trends (147 higher abundance vs. 74 lower abundance). Hierarchical cluster analysis of differential metabolites between diploid and tetraploid species showed a clear grouping pattern, in which the expression abundance of lipids, amino acids and derivatives, and phenolic acids increased in tetraploids. Further analysis revealed that the lipids in tetraploid rice increased significantly, especially unsaturated fatty acids and phospholipids. This study provides further basis for understanding the changes in rice nutritional quality following polyploidization and may serve as a new theoretical reference for breeding eutrophic or functional rice varieties via polyploidization.

Lipidomics reveals the changes in non-starch and starch lipids of rice (Oryza sativa L.) during storage

In the current study, the changes of non-starch and starch lipids in two rice varieties during storage were investigated based on untargeted lipidomic approach. A total of 395 non-starch lipids and 13 starch lipids were identified in two rice varieties. 171 lipids in Nanjing and 6 lipids in Jianzhen were significantly different in stored rice compared to those in the fresh ones. Bioinformatics analysis on these significantly different lipids revealed that the two rice varieties possessed different lipids metabolic pathways during storage. Our study provides insights into the mechanism of the changes in non-starch and starch lipids in rice during storage.

Protective Mechanism of Rice-Derived Lipids and Glucosylceramide in an In Vitro Intestinal Tract Model

We previously reported that the ethanol extract from polished rice suppresses inflammation and the formation of aberrant crypt foci in the mouse colon and particularly focused on the plant sphingolipid glucosylceramide (GlcCer). Here, we investigated the effects of rice lipid fractions and GlcCer on differentiated Caco-2 cells treated with lipopolysaccharide (LPS), in particular, we evaluated the mechanism of action of GlcCer using related substances and metabolic enzyme inhibitors. Rice-derived polar lipids suppressed the LPS-induced reduction in the number of cells. The polar lipids with higher GlcCer content exerted a better effect than the other fractions. GlcCer-related substances reversed the LPS-induced reduction in the number of cells, and GlcCer-metabolic inhibitors, including a sphingosine kinase inhibitor, suppressed the beneficial effects of GlcCer-related substances. These results suggest that GlcCer is a rice component with intestinal protection. Secondly, GlcCer is metabolized during inflammation and protects intestinal cells by maintaining the sphingolipid levels in cells and producing sphingoid base-1-phosphate.

Effect of protein denaturation and lipid removal on rice physicochemical properties

The physicochemical properties of rice are influenced by their chemical components and their interactions. It has been demonstrated that the interactions among rice chemical components are enhanced by protein denaturation (PD) via heat treatment and by lipid removal (LR) via solvent extraction. The objective of this study was to investigate the impacts of PD, LR, and their combined treatments on the gelatinization and pasting properties, swelling power, and water solubility of four brown rice flours. Rice protein was denatured under a vacuum at 100 °C, and rice lipid was removed via hexane for varying times. The combined treatments were done in two ways, PD followed by LR (PD-LR), and LR followed by PD (LR-PD). The results showed that PD increased gelatinization temperatures, while LR decreased gelatinization temperatures. Both PD and LR reduced pasting and swelling properties; however, PD resulted in a greater decrease than LR. Polar lipids are proposed to serve as bridges to link denatured proteins and starch granules in the combined treatments, resulting in greater decreases in the pasting and swelling properties than the individual treatments. The results obtained in this study demonstrate the importance of starch-lipid-protein interactions on the physicochemical properties of brown rice flour.

The lipid transfer protein OsLTPL159 is involved in cold tolerance at the early seedling stage in rice.

SummaryNonspecific lipid transfer proteins (nsLTPs) play critical roles in plant development and response to abiotic stresses. Here, we found that a rice lipid transfer protein, OsLTPL159, was associated with cold tolerance at the early seedling stage. Overexpression of an OsLTPL159 IL 112 allele from the cold‐tolerant introgression line IL112 in either the japonica variety Zhonghua17 (ZH17) or the indica variety Teqing background dramatically enhanced cold tolerance. In addition, down‐regulation of the expression of OsLTPL159 in the japonica variety ZH17 by RNA interference (RNAi) significantly decreased cold tolerance. Further transcriptomic, physiological and histological analysis showed that the OsLTPL159 IL 112 allele likely enhanced the cold tolerance of rice at the early seedling stage by decreasing the toxic effect of reactive oxygen species, enhancing cellulose deposition in the cell wall and promoting osmolyte accumulation, thereby maintaining the integrity of the chloroplasts. Notably, overexpression of another allele, OsLTPL159 GC 2, from the recipient parent Guichao 2 (GC2), an indica variety, did not improve cold tolerance, indicating that the variations in the OsLTPL159 coding region of GC2 might disrupt its function for cold tolerance. Further sequence comparison found that all 22 japonica varieties surveyed had an OsLTPL159 haplotype identical to IL112 and were more cold‐tolerant than the surveyed indica varieties, implying that the variations in OsLTPL159 might be associated with differential cold tolerance of japonica and indica rice. Therefore, our findings suggest that the OsLTPL159 allele of japonica rice could be used to improve cold tolerance of indica rice through a molecular breeding strategy.

Influence of gene regulation on rice quality: Impact of storage temperature and humidity on flavor profile

Effects of high temperature-high humidity (HT-HH) storage on the flavor profile of rice were investigated. Volatile compounds such as aldehydes, ketones, and furans increased when rice was stored under HT-HH conditions, leading to a pronounced deterioration in rice quality. Correspondingly, the fatty acid content of the rice significantly increased during storage. Lipid oxidation was also accelerated under HT-HH conditions leading to the formation of peroxides. However, catalase activity was reduced under these conditions promoting the accumulation of peroxides. For the first time, insights into the genetic mechanisms responsible for these changes were obtained using RNA-sequencing to establish the flavor metabolic pathways in rice. Under HT-HH conditions, gene expression of lipase increased while that of catalase decreased, leading to faster hydrolysis and oxidation of the rice lipids. As a result, a series of lipid degradation products was formed (such as fatty acids, aldehydes, and ketones) that decreased the rice flavor quality.

Optimization of rice lipid production from ultrasound-assisted extraction by response surface methodology

In this work, a new method of ultrasound-assisted extraction (UAE) of rice lipid was proposed. From the single-factor experimental design, extraction with hexane resulted in the highest yield compared to petroleum ether and isopropanol. The amount of extracted rice lipids yields enhanced with increasing sonication power, temperature and time, respectively. However, excessive sonication power, temperature and prolonged time would lead to the decrease of rice lipid. A response surface methodology (RSM) was used to optimize the parameters on UAE based on single factor experiment. Optimum combinations for lipid extraction yield (77.31%) were hexane, 123W, 42 °C and 37 min. The compositions of lipid were obtained by gas chromatography and mass spectrometry (GC-MS) and no significant differences were observed between UAE and conventional method.

Over-expression of Arabidopsis thaliana SFD1/GLY1, the gene encoding plastid localized glycerol-3-phosphate dehydrogenase, increases plastidic lipid content in transgenic rice plants

Lipids are the major constituents of all membranous structures in plants. Plants possess two pathways for lipid biosynthesis: the prokaryotic pathway (i.e., plastidic pathway) and the eukaryotic pathway (i.e., endoplasmic-reticulum (ER) pathway). Whereas some plants synthesize galactolipids from diacylglycerol assembled in the plastid, others, including rice, derive their galactolipids from diacylglycerols assembled by the eukaryotic pathway. Arabidopsis thaliana glycerol-3-phosphate dehydrogenase (G3pDH), coded by SUPPRESSOR OF FATTY ACID DESATURASE 1 (SFD1; alias GLY1) gene, catalyzes the formation of glycerol 3-phosphate (G3p), the backbone of many membrane lipids. Here SFD1 was introduced to rice as a transgene. Arabidopsis SFD1 localizes in rice plastids and its over-expression increases plastidic membrane lipid content in transgenic rice plants without any major impact on ER lipids. The results suggest that over-expression of plastidic G3pDH enhances biosynthesis of plastid-localized lipids in rice. Lipid composition in the transgenic plants is consistent with increased phosphatidylglycerol synthesis in the plastid and increased galactolipid synthesis from diacylglycerol produced via the ER pathway. The transgenic plants show a higher photosynthetic assimilation rate, suggesting a possible application of this finding in crop improvement.

Genes involved in the accumulation of starch and lipids in wheat and rice: characterization using molecular and cytogenetic techniques

This review covers the molecular characterization of starch biosynthetic genes by the Starch group based in CSIRO, Canberra which benefitted enormously from the interactions with Prof Mukai and his group in Osaka. A number of genes involved in starch biosynthesis in wheat were isolated from the D- genome donor of wheat, Aegilops tauschii. These were usually isolated as lambda clones and therefore their location on chromosomes could only be determined with further work. This gap was filled by the cytogenetic work carried out by Prof Mukai’s group. In addition, when larger BAC clones were isolated, it was often possible by cytogenetics to visualize the organization of multiple genes and to confirm and sometimes correct conclusions from sequencing. New planned work in starch and lipid accumulation at Monash Malaysia is briefly mentioned.

단백질과 지방첨가가 약주의 품질특성에 미치는 영향

In this study, the fermentation characteristics of Yakju were investigated by addition of protein and lipid. These are classified according to raw material (rice, glucose) and inducing substance (rice protein, rice lipid). Alcoholic fermentation occurred at 25°C, after 14 days. The results of this study were as follows: Alcohol content of Yakju with rice protein was higher than those of other samples. The pH and glucose of rice Yakju were detemied to be 4.86~5.13 and 4.17~4.86, respectively. Titratable acid and the total amino acid content of the Yakju with rice protein were the highest among other samples. The optical density contents of the rice Yakju and glucose Yakju were 0.52~0.653 and 0.27~0.61, respectively. The concentration of organic acids in rice Yakju (433.98~519.31 mg%) was higher than that of glucose Yakju (303.76~387.50 mg%). The major organic acid components of the Yakju were succinic, citric, acetic and lactic acids. The nitrogen compound concentrations of rice Yakju (4377.38~10208.06 ppm) was higher than that of glucose Yakju (671.20~9368.93 ppm). The protein odor correlation coefficient was 0.98 (p<0.001) showing a very high correlation coefficient, while lipid odor coefficient showed a negative correlation with -0.038 (p<0.458).

Differentiation of rice varieties using small bioactive lipids as markers

Steryl ferulates (γ‐oryzanol) are a group of important lipid antioxidants found in rice. This study uses OMIC‐technologies to differentiate between rice varieties based on these minor bioactive lipids. The γ‐oryzanol rich‐lipid fractions were first extracted from six types of common cargo rice and two types of wild rice, which were subsequently analyzed using ultra performance liquid chromatography with high‐resolution quadrupole time‐of‐flight mass spectrometric detection (UPLC‐HR‐Q‐TOF‐MS). Unique spectral profiles were produced for each rice variety, and the MS data was further converted into markers. Multivariate statistical analysis including principal component analysis (PCA) and the observed partial least squares‐discriminant analysis (OPLS‐DA) was utilized to find the characteristic markers, enabling us to differentiate between various rice varieties based on their steryl ferulate profiles and other small lipids.Practical applications: This study provides a targeted method to distinguish between various common rice varieties as well as wild rice from different geographic regions, which could be a new approach for rice authentication. Additionally, this sensitive analytical technique may reveal several new compounds of bioactive lipids in rice. Furthermore, the OMIC approach to rice differentiation also has the potential to lead to the selection of rice varieties with optimal profiles of bioactive lipids for food use.Our study provides a novel and targeted method to distinguish between rice varieties using UPLC‐HR‐Q‐TOF‐MS with the OMIC technique. We were able to find characteristic markers that can classify different rice types based on their steryl ferulate profiles and other potential small lipids.