Volatile components in stored rice [Oryza sativa (L.)] of varieties with and without lipoxygenase-3 in seeds

Rice seed storability: From molecular mechanisms to agricultural practices

The storability of rice seeds is crucial for ensuring flexible planting options, agricultural seed security, and global food safety. With the intensification of global climate change and the constant fluctuations in agricultural production conditions, enhancing the storability of rice seeds has become particularly important. Seed storability is a complex quantitative trait regulated by both genetic and environmental factors. This article reviews the main regulatory mechanisms of rice seed storability, including the accumulation of seed storage proteins, late embryogenesis abundant (LEA) proteins, heat shock proteins, sugar signaling, hormonal regulation by gibberellins and abscisic acid, and the role of the ubiquitination pathway. Additionally, this article explores the improvement of storability using wild rice genes, molecular marker-assisted selection, and gene editing techniques such as CRISPR/Cas9 in rice breeding. By providing a comprehensive scientific foundation and practical guidance, this review aims to promote the development of rice varieties with enhanced storability to meet evolving agricultural demands.

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.

A signaling cascade mediating fruit trait development via phosphorylation-modulated nuclear accumulation of JAZ repressor

It is generally accepted that jasmonate-ZIM domain (JAZ) repressors act to mediate jasmonate (JA) signaling via CORONATINE-INSENSITIVE1 (COI1)-mediated degradation. Here, we report a cryptic signaling cascade where a JAZ repressor, FvJAZ12, mediates multiple signaling inputs via phosphorylation-modulated subcellular translocation rather than the COI1-mediated degradation mechanism in strawberry (Fragaria vesca). FvJAZ12 acts to regulate flavor metabolism and defense response, and was found to be the target of FvMPK6, a mitogen-activated protein kinase that is capable of responding to multiple signal stimuli. FvMPK6 phosphorylates FvJAZ12 at the amino acid residues S179 and T183 adjacent to the PY residues, thereby attenuating its nuclear accumulation and relieving its repression for FvMYC2, which acts to control the expression of lipoxygenase 3 (FvLOX3), an important gene involved in JA biosynthesis and a diverse array of cellular metabolisms. Our data reveal a previously unreported mechanism for JA signaling and decipher a signaling cascade that links multiple signaling inputs with fruit trait development.

Genome-wide identification and expression pattern analysis of lipoxygenase genes of chickpea (Cicer arietinum L.) in response to accelerated aging

Seed aging is a major problem which is caused by various factors such as unfavorable physiological, biochemical, and metabolic alterations in seed cells. Lipoxygenase (LOXs), an oxidoreductase enzyme that catalyzes the oxidation of polyunsaturated fatty acids, acts as a negative regulator in seed viability and vigour during storage. In this study, we identified ten putative LOX gene family members in the chickpea genome, designated as "CaLOX" which are mainly located in the cytoplasm and chloroplast. These genes share different physiochemical properties and similarities in their gene structures and conserved functional regions. The promoter region contained the cis-regulatory elements and transcription binding factors, which were mainly linked to biotic and abiotic stress, hormones, and light responsiveness. In this study, chickpea seeds were treated with accelerated aging treatment for 0, 2, and 4 days at 45°C and 85 % relative humidity. Increased level of reactive oxygen species, malondialdehyde, electrolyte leakage, proline, lipoxygenase (LOX) activity, and decreased catalase activity indicates cellular dysfunction and demonstrated seed deterioration. Quantitative real-time analysis reveals that 6 CaLOX genes were upregulated, and 4 CaLOX genes were downregulated during the seed aging process in chickpea. This comprehensive study will reveal the role of the CaLOX gene in response to aging treatment. The identified gene may be used to develop better-quality seeds in chickpea.

Dynamic Changes in Volatiles, Soluble Sugars, and Fatty Acids in Glutinous Rice during Cooking

Cooking is an important process before rice is consumed and constitutes the key process for rice flavor formation. In this paper, dynamic changes in aroma- and sweetness-related compounds were tracked during the entire cooking process (including washing with water, presoaking, and hydrothermal cooking). The volatiles, fatty acids, and soluble sugars in raw rice, washed rice, presoaked rice, and cooked rice were compared. After being washed with water, the total volatiles decreased while aldehydes and unsaturated fatty acids increased. Meanwhile, oligosaccharides decreased and monosaccharides increased. The changes in fatty acids and soluble sugars caused by the presoaking process were similar to those in the water-washing process. However, different changes were observed for volatiles, especially aldehydes and ketone. After hydrothermal cooking, furans, aldehydes, alcohols, and esters increased while hydrocarbons and aromatics decreased. Moreover, all fatty acids increased; among these, oleic acids and linoleic acid increased most. Unlike with washing and presoaking, all soluble sugars except fructose increased after hydrothermal cooking. Principal component analysis showed that cooked rice possessed a volatile profile that was quite different from that of uncooked rice, while washed rice and presoaked rice possessed similar volatile profiles. These results indicated that hydrothermal cooking is the pivotal process for rice flavor formation.

Dissecting the biochemical and molecular-genetic regulation of diverse metabolic pathways governing aroma formation in indigenous aromatic indica rice varieties

BACKGROUND

Aromatic rice is characterized by its distinct flavor and fragrance, imparted by more than 200 volatile organic compounds. The desirable trait of aroma relies on the type of the variety, with some varieties exhibiting considerably higher aroma content. This prompted us to undergo an exhaustive study of the aroma-associated biochemical pathways and expression of related genes, encoding the enzymes involved in those pathways in indigenous aromatic rice cultivars.

METHODS AND RESULTS

The higher aroma level in aromatic rice varieties was attributed to higher transcript levels of PDH, P5CS, OAT, ODC, DAO and TPI, but lower P5CDH and BADH2, as revealed by comparative expression profiling of genes in 11 aromatic and four non-aromatic varieties. Some of the high-aroma containing varieties exhibited lower expression of SPDS and SPMS genes, concomitant with higher PAO expression. Protein immunoblot analyses showed lesser BADH2 protein accumulation in the aromatic varieties. The involvement of shikimate pathway in aroma formation was justified by higher levels of shikimic and ferulic acids due to higher expression of SK1, SK2 and ARD genes. The aromatic varieties exhibited higher expression of LOX3 and HPL, with higher corresponding enzyme activity, accompanied with lower accumulation of lipid hydroperoxides and higher level of total terpenoids, signifying the role of oxylipin pathway and terpene-related volatiles in aroma formation. The pattern of transcript level and metabolite accumulation followed the same trend in both vegetative (seedling) and reproductive (seed) tissues. Sequence analyses revealed several mutations in the upstream region and different exons and introns of BADH2 in the examined aromatic varieties. The allele specific marker system acted as fingerprint to distinguish the selected aromatic rice varieties. The cleaved amplified polymorphic sequence marker established the absence of any mutation in the 14th exon of BADH2 in the aromatic varieties.

CONCLUSION

The present work clearly highlighted the biochemical and molecular-genetic mechanism of differential aroma levels which could be attributed to differential regulation of metabolites and genes, belonging to 2-acetyl-1-pyrroline, shikimate, oxylipin and terpenoid metabolic pathways in the indigenous aromatic rice varieties.

Detection of the freshness of rice by chemiluminescence

Reactive oxygen species (ROS) are usually produced in rice under aerobic environmental conditions, resulting in peroxidative changes in polyunsaturated fatty acids, and affecting the deterioration of rice during storage. In addition, as an important enzyme that participates in removing ROS, peroxidase is also present in rice, and takes part in protecting rice from attack by ROS. Moreover, loss of peroxidase activity may give rise to rice deterioration during storage. Therefore, measuring peroxidase activity makes it possible to ascertain the freshness of rice. In addition, peroxidase can also catalyze the luminol-hydrogen peroxide system. Based on this, in this work we established a new chemiluminescence (CL) method that was used to detect the freshness of stored rice. Under optimal experimental conditions, we showed that the freshness of rice can be measured using this CL method. This study is the first to detect the freshness of rice using a CL method, opening up a novel direction for the application of CL.

Molecular Hydrogen Improves Rice Storage Quality via Alleviating Lipid Deterioration and Maintaining Nutritional Values

Improvement of the storage quality of rice is a critical challenge for the scientific community. This study assesses the effects of the irrigation with hydrogen nanobubble water (HNW) on the storage quality of rice (Oryza sativa 'Huruan1212'). Compared with ditch water control, after one year of storage at 25 °C and 70% RH, the HNW-irrigated rice had higher contents of essential amino acids, especially lysine. Importantly, the generation of off-flavors in the stored rice was significantly decreased, which was confirmed by the lower levels of volatile substances, including pentanal, hexanal, heptanal, octanal, 1-octen-3-ol, and 2-heptanone. The subsequent results showed that the HNW-irrigated rice not only retained lower levels of free fatty acid values, but also had increased antioxidant capacity and decreased lipoxygenase activity and transcripts, thus resulting in decreased lipid peroxidation. This study opens a new window for the practical application of HNW irrigation in the production and subsequent storage of crops.

A comparative HS-SPME/GC-MS-based metabolomics approach for discriminating selected japonica rice varieties from different regions of China in raw and cooked form

Japonica rice is widely planted in different regions of China. Rice of different geographical origins may have substantially different economic values. In this study, An untargeted metabolomics based approach using headspace solid-phase microextraction coupled to gas chromatography-mass spectrometry (HS-SPME/GC-MS) was applied to distinguish 27 japonica rice varieties originated from South, Northern and Northeastern China in raw and cooked form, respectively. Orthogonal partial least-squares discriminant analysis (OPLS-DA) models exhibited good geographic discrimination. Sixteen and twenty-two volatiles were selected as the discriminant markers in raw and cooked rice, respectively. However, only hexanal, 3,5-octadien-2-one and 2-butyl-2-octenal were selected both in raw and cooked rice. Markers in raw rice mainly involved in terpenes, lipoxygenases, indole, and shikimate and benzoic acid pathways. Markers in cooked rice were mainly derived from lipid oxidation. The results provided a deeper understanding of volatiles variation of rice in China from different geographic origins.

A review of thermosensitive antinutritional factors in plant-based foods

Legumes and cereals account for the vast proportion of people's daily intake of plant-based foods. Meanwhile, a large number of antinutritional factors in legumes and cereals hinder the body absorption of nutrients and reduce the nutritional value of food. In this paper, the antinutritional effects, determination, and passivation methods of thermosensitive antinutritional factors such as trypsin inhibitors, urease, lipoxygenase, and lectin were reviewed to provide theoretical help to reduce antinutritional factors in food and improve the utilization rate of plant-based food nutrition. Since trypsin inhibitors and lectin have been more extensively studied and reviewed previously, the review mainly focused on urease and lipoxygenase. This review summarized the information of thermosensitive antinutritional factors, trypsin inhibitors, urease, lipoxygenase, and lectin, in cereals and legumes. The antinutritional effects, and physical and chemical properties of trypsin inhibitors, urease, lipoxygenase, and lectin were introduced. At the same time, the research methods for the detection and inactivation of these four antinutritional factors were also summarized in the order of research conducted time. The rapid determination and inactivation of antinutrients will be the focus of attention for the food industry in the future to improve the nutritional value of food. Exploring what structural changes could passivation technologies bring to antinutritional factors will provide a theoretical basis for further understanding the mechanisms of antinutritional factor inactivation. PRACTICAL APPLICATIONS: Antinutritional factors in plant-based foods hinder the absorption of nutrients and reduce the nutritional value of the food. Among them, thermosensitive antinutritional factors, such as trypsin inhibitors, urease, lipoxygenase, and lectins, have a high proportion among the antinutritional factors. In this paper, we investigate thermosensitive antinutritional factors from three perspectives: the antinutritional effect of thermosensitive antinutritional factors, determination, and passivation methods. The current passivation methods for thermosensitive antinutritional factors revolve around biological, physical, and chemical aspects, and their elimination mechanisms still need further research, especially at the protein structure level. Reducing the level of antinutritional factors in the future food industry while controlling the loss of other nutrients in food is a goal that needs to be balanced. This paper reviews the antinutritional effects of thermosensitive antinutritional factors and passivation methods, expecting to provide new research ideas to improve the nutrient utilization of food.

A novel LOX3-null allele (lox3-b) originated in the aromatic Basmati rice cultivars imparts storage stability to rice bran

Rapid deterioration of rice bran due to the LOX3 enzyme catalysed oxidation of PUFA is the major bottleneck for its utilization in various downstream applications. In the present study, we have identified a set of nine novel LOX3-null rice accessions carrying a deletion of C residue in the exon2 causing a frameshift mutation resulting in a truncated non-functional LOX3 protein. Our study, further manifested the predominance of C deletion based LOX3-null allele, named lox3-b, in the aromatic rice germplasm particularly in the Indian Basmati rice group. The LOX3-null genotypes exhibited significantly reduced rancidity, after six months of storage. They also showed significantly lower percentage reduction of linoleic acid (LA), higher γ-oryzanol content and lower hexanal content. A functional dCAPS marker designed based on the deletion polymorphism clearly differentiated LOX3 and lox3-b alleles, and has the potential application in marker assisted rice breeding programmes to develop cultivars with better bran storability.

Carotenoid stability and aroma retention during the post-harvest storage of biofortified maize

BACKGROUND

Maize varieties that are rich in carotenoids have been developed to combat vitamin A deficiency in Sub-Saharan Africa. Unfortunately, after harvest, carotenoids degrade and off-flavor volatiles develop, which affect nutrient intake and consumer acceptance. This study evaluated carotenoid retention and aroma compound stability in provitamin A biofortified maize, variety Pool 8A, as influenced by dry milling and storage in different packaging and temperature conditions.

RESULTS

The lowest amount of total carotenoids was found in flour stored in laminated paper bags at 37 °C (only 16% retention after 180 days), attributable to the high storage temperature and oxygen permeability of the packaging material. No significant effect on carotenoid degradation was found for dry milling, either by rotor mill or freezer mill, but the formation of volatile compounds was significantly (P < 0.05) affected. Volatile compounds such as hexanal, 2-pentylfuran, 1-propanol, 2-heptanone, butyrolactone, limonene, and hexanoic acid were found in different proportions after milling. The highest concentration of hexanal was in flour milled by rotor mill or freezer mill, and stored in laminated paper bags at 37 °C after 180 days, and the lowest concentrations were for flour in aluminium bags and double-layered polyethylene bags stored at 4 °C.

CONCLUSION

Maize flour stored in double-layered polyethylene bags had the highest carotenoid retention and aroma stability. Importantly, the use of these bags is economically feasible in low-income countries. Overall, our results show that effective control of storage conditions is crucial to prevent carotenoid loss and decrease off-odor formation. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Novel allelic variation in the Phospholipase D alpha1 gene (OsPLDα1) of wild Oryza species implies to its low expression in rice bran

Rice bran, a by-product after milling, is a rich source of phytonutrients like oryzanols, tocopherols, tocotrienols, phytosterols, and dietary fibers. Moreover, exceptional properties of the rice bran oil make it unparalleled to other vegetable oils. However, a lipolytic enzyme Phospholipase D alpha1 (OsPLDα1) causes rancidity and ‘stale flavor’ in the oil, and thus limits the rice bran usage for human consumption. To improve the rice bran quality, sequence based allele mining at OsPLDα1 locus (3.6 Kb) was performed across 48 accessions representing 11 wild Oryza species, 8 accessions of African cultivated rice, and 7 Oryza sativa cultivars. From comparative sequence analysis, 216 SNPs and 30 InDels were detected at the OsPLDα1 locus. Phylogenetic analysis revealed 20 OsPLDα1 cDNA variants which further translated into 12 protein variants. The O. officinalis protein variant, when compared to Nipponbare, showed maximum variability comprising 22 amino acid substitutions and absence of two peptides and two β-sheets. Further, expression profiling indicated significant differences in transcript abundance within as well as between the OsPLDα1 variants. Also, a new OsPLDα1 transcript variant having third exon missing in it, Os01t0172400-06, has been revealed. An O. officinalis accession (IRGC101152) had lowest gene expression which suggests the presence of novel allele, named as OsPLDα1-1a (GenBank accession no. MF966931). The identified novel allele could be further deployed in the breeding programs to overcome rice bran rancidity in elite cultivars.

Present status and future perspectives of breeding for buckwheat quality

Buckwheat is an important crop globally. It has been processed into cereal grain, noodles, confectionery, bread, and fermented foods for many years. Buckwheat production and processing has supported local economies and is deeply related to the culture of some regions. Buckwheat has many unique traits as a food, with a good flavor and color. In addition, buckwheat is also a healthy food because it contains bioactive compounds that have anti-oxidative, anti-hypertensive, and anti-obesity properties. Therefore, breeding of buckwheat for quality is an important issue to be addressed. Compared to other crops, there is still a lack of basic information on quality, including bioactive compounds generation and enhancement. However, some mechanisms for modifying and improving the quality of buckwheat varieties have recently been identified. Further, some varieties with improved quality have recently been developed. In this review, we summarize the issues around buckwheat quality and review the present status and future potential of buckwheat breeding for quality.

Development and characterization of marker-free and transgene insertion site-defined transgenic wheat with improved grain storability and fatty acid content

Development of marker-free and transgene insertion site-defined (MFTID) transgenic plants is essential for safe application of transgenic crops. However, MFTID plants have not been reported for wheat (Triticum aestivum). Here, we prepared a RNAi cassette for suppressing lipoxygenase (LOX) gene expression in wheat grains using a double right border T-DNA vector. The resultant construct was introduced into wheat genome via Agrobacterium-mediated transformation, with four homozygous marker-free transgenic lines (namely GLRW-1, -3, -5 and -8) developed. Aided by the newly published wheat genome sequence, the T-DNA insertion sites in GLRW-3 and GLRW-8 were elucidated at base-pair resolution. While the T-DNA in GLRW-3 inserted in an intergenic region, that of GLRW-8 inactivated an endogenous gene, which was thus excluded from further analysis. Compared to wild -type (WT) control, GLRW-1, -3 and -5 showed decreased LOX gene expression, lower LOX activity and less lipid peroxidation in the grains; they also exhibited significantly higher germination rates and better seedling growth after artificial ageing treatment. Interestingly, the three GLRW lines also had substantially increased contents of several fatty acids (e.g., linoleic acid and linolenic acid) in their grain and flour samples than WT control. Collectively, our data suggest that suppression of grain LOX activity can be employed to improve the storability and fatty acid content of wheat seeds and that the MFTID line GLRW-3 is likely of commercial value. Our approach may also be useful for developing the MFTID transgenic lines of other crops with enhanced grain storability and fatty acid content.

Novel cis-acting regulatory elements in wild Oryza species impart improved rice bran quality by lowering the expression of phospholipase D alpha1 enzyme (OsPLDα1)

Rice bran oil is good quality edible oil, rich in antioxidants and comprised typically of oleic-linoleic type fatty acids. However, presence of a highly lipolytic enzyme Phospholipase D alpha1 (OsPLDα1) increases free fatty acid content in the oil which further leads to stale flavor and rancidity of the oil, making it unfit for human consumption. In this study, we compared the upstream regions of OsPLDα1 orthologs across 34 accessions representing 5 wild Oryza species and 8 cultivars, to uncover sequence variations and identify cis-elements involved in differential transcription of orthologs. Alignment of the upstream sequences to the Nipponbare OsPLDα1 reference sequence revealed the presence of 39 SNPs. Phylogenetic analysis showed that all the selected cultivars and wild species accessions are closely related to the reference except for three accessions of O. rufipogon (IRGC89224, IRGC104425, and IRGC105902). Furthermore, using exon-specific qRT-PCR, OsPLDα1 expression patterns in immature grains indicated significant differences in transcript abundance between the wild species accessions. In comparison to the control, lowest gene expression was observed in IRGC89224 accession (0.20-fold) followed by IRGC105902 (0.26-fold) and IRGC104425 (0.41-fold) accessions. In-silico analysis of the OsPLDα1 promoter revealed that the copy number variations of CGCGBOXAT, GT1CONSENSUS, IBOXCORE, NODCON2GM, OSE2ROOTNODULE, SURECOREATSULTR11, and SORLIP1AT cis-elements play an important role in the transcriptional activities of orthologous genes. Owing to the presence of ARFAT and SEBF elements only in the IRGC89224 accession, which had the lowest gene expression as well, these putative upstream regulatory sequences have been identified as novel cis-elements which may act as repressors in regulating the OsPLDα1 gene expression. The accessions identified with low OsPLDα1 expressions could be further deployed as potential donors of ideal OsPLDα1 allele for transfer of the desired trait into elite rice cultivars.

Rapid Determination of the Freshness of Lotus Seeds Using Surface Desorption Atmospheric Pressure Chemical Ionization-Mass Spectrometry with Multivariate Analyses

In order to explore a new method to detect the freshness of lotus seeds, the lotus seeds stored for 0, 1, 2, and 3 years, respectively, were used as experimental materials and analyzed by DAPCI-MS (desorption atmospheric pressure chemical ionization-mass spectrometry). The obtained data were processed by principal component analysis (PCA) and backpropagation artificial neural networks (BP-ANNs). The result showed that DAPCI-MS could obtain abundant chemical material information from the slice surface of lotus seeds. The BP-ANNs model could be applied not only to distinguish fresh and aged lotus seeds with the testing set accuracies of 95.0% and 91.7%, respectively, but also to classify lotus seeds with different storage times with the testing set accuracies of 90.0%, 85.0%, 85.0%, and 90.0%, respectively. The paper developed a fast, convenient, and accurate method for the freshness detection of lotus seed and would provide reliable reference value for rapid authentication of food freshness by the rapid mass spectrometry technique.

Phytochemical Analysis and Potential Biological Activities of Essential Oil from Rice Leaf

Although many investigations on phytochemicals in rice plant parts and root exudates have been conducted, information on the chemical profile of essential oil (EO) and potent biological activities has been limited. In this study, chemical compositions of rice leaf EO and in vitro biological activities were investigated. From 1.5 kg of fresh rice leaves, an amount of 20 mg EO was obtained by distillation and analyzed by gas chromatography-mass spectrometry (GC-MS), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) to reveal the presence of twelve volatile constituents, of which methyl ricinoleate (27.86%) was the principal compound, followed by palmitic acid (17.34%), and linolenic acid (11.16%), while 2-pentadecanone was the least (2.13%). Two phytoalexin momilactones A and B were first time identified in EO using ultra-performance liquid chromatography coupled with electrospray mass spectrometry (UPLC/ESI-MS) (9.80 and 4.93 ng/g fresh weight, respectively), which accounted for 7.35% and 3.70% of the EO, respectively. The assays of DPPH (IC50 = 73.1 µg/mL), ABTS (IC50 = 198.3 µg/mL), FRAP (IC50 = 700.8 µg/mL) and β-carotene oxidation (LPI = 79%) revealed that EO possessed an excellent antioxidant activity. The xanthine oxidase assay indicated that the anti-hyperuricemia potential was in a moderate level (IC50 = 526 µg/mL) as compared with the standard allopurinol. The EO exerted potent inhibition on growth of Raphanus sativus, Lactuca sativa, and two noxious weeds Echinochloa crus-galli, and Bidens pilosa, but in contrast, the growth of rice seedlings was promoted. Among the examined plants, the growth of the E. crus-galli root was the most inhibited, proposing that constituents found in EO may have potential for the control of the problematic paddy weed E. crus-galli. It was found that the EO of rice leaves contained rich phytochemicals, which were potent in antioxidants and gout treatment, as well as weed management. Findings of this study highlighted the potential value of rice leaves, which may provide extra benefits for rice farmers.

Production of high oleic/low linoleic rice by genome editing

Rice bran oil (RBO) contains many valuable healthy constituents, including oleic acid. Improvement of the fatty acid composition in RBO, including an increase in the content of oleic acid, which helps suppress lifestyle disease, would increase health benefits. The enzyme fatty acid desaturase 2 (FAD2) catalyzes the conversion of oleic acid to linoleic acid in plants, and FAD2 mutants exhibit altered oleic and linoleic acid content in many crops. There are three functional FAD2 genes in the genome of rice (Oryza sativa L.), and, of these, expression of the OsFAD2-1 gene is highest in rice seeds. In order to produce high oleic/low linoleic RBO, we attempted to disrupt the OsFAD2-1 gene by CRISPR/Cas9-mediated targeted mutagenesis. We succeeded in the production of homozygous OsFAD2-1 knockout rice plants. The content of oleic acid increased to more than twice that of wild type, and, surprisingly, linoleic acid, a catabolite of oleic acid by FAD2, decreased dramatically to undetectable levels in fad2-1 mutant brown rice seeds. In this study, by genome editing based on genome information, we succeeded in the production of rice whose fatty acid composition is greatly improved. We suggest that CRISPR/Cas9-mediated mutagenesis of a major gene that shows dominant expression in the target tissue could be a powerful tool to improve target traits in a tissue-specific manner.

Suppression of LOX activity enhanced seed vigour and longevity of tobacco (Nicotiana tabacum L.) seeds during storage

The preservation of seed viability and quality in storage is an important trait both for commercial and germplasm usage. To better explore potential mechanisms of tobacco seed deterioration, seed packed in cloth bag (C) and vacuum bag (V) were stored under room temperature (RT) and low temperature (LT, 18°C), and sampled periodically for laboratory testing. Seed stored in low temperature with vacuum bag (LT/V) owned the highest seed vigour after 25 months of storage and in room temperature with cloth bag (RT/C) lost seed vigour and germination ability after 20-month storage. Meanwhile, seed in RT/C notably increased about 5-fold endogenous hydrogen peroxide (H₂O₂), 4-fold malondialdehyde (MDA) contents, 12-fold Lipoxygenases (LOX) activity and 2-fold the expression of NtLOX3 comparing with LT/V at the end of 15-month storage. In addition, regression analysis indicated that LOX activity was strongly negatively correlated with seed vigour as the R ² value reached 0.970 in RT/C. Furthermore, caffeic acid and catechin, the inhibitors of LOX activity, were applied to tobacco seeds pre-treatment and followed with artificial accelerated aging. Seeds pretreated with inhibitors, especially caffeic acid, reduced LOX activity by 50%, MDA and H₂O₂ contents by 40% and 20%, respectively, and increased more than 1.2-fold seed vigour and seedling quality comparing with seeds pretreated with H₂O after 6-day artificial aging, indicating a better seed storability after artificial accelerated aging. These results suggest that LOX accelerated seed aging, and suppression of LOX activity enhanced seed vigour and viability in accelerated aging tobacco seed, opening new opportunities for effective management of seed germplasm under long-term storage and conservation.

Identification of a novel SPLIT-HULL (SPH) gene associated with hull splitting in rice (Oryza sativa L.)

The split-hull phenotype caused by reduced lemma width and low lignin content is under control of SPH encoding a type-2 13-lipoxygenase and contributes to high dehulling efficiency. Rice hulls consist of two bract-like structures, the lemma and palea. The hull is an important organ that helps to protect seeds from environmental stress, determines seed shape, and ensures grain filling. Achieving optimal hull size and morphology is beneficial for seed development. We characterized the split-hull (sph) mutant in rice, which exhibits hull splitting in the interlocking part between lemma and palea and/or the folded part of the lemma during the grain filling stage. Morphological and chemical analysis revealed that reduction in the width of the lemma and lignin content of the hull in the sph mutant might be the cause of hull splitting. Genetic analysis indicated that the mutant phenotype was controlled by a single recessive gene, sph (Os04g0447100), which encodes a type-2 13-lipoxygenase. SPH knockout and knockdown transgenic plants displayed the same split-hull phenotype as in the mutant. The sph mutant showed significantly higher linoleic and linolenic acid (substrates of lipoxygenase) contents in spikelets compared to the wild type. It is probably due to the genetic defect of SPH and subsequent decrease in lipoxygenase activity. In dehulling experiment, the sph mutant showed high dehulling efficiency even by a weak tearing force in a dehulling machine. Collectively, the results provide a basis for understanding of the functional role of lipoxygenase in structure and maintenance of hulls, and would facilitate breeding of easy-dehulling rice.

Aroma volatile analyses and 2AP characterization at various developmental stages in Basmati and Non-Basmati scented rice (Oryza sativa L.) cultivars

BACKGROUND

Rice plant growth is comprised of distinct phases, such as vegetative, reproductive, grain filling and maturity phases. In these phases synthesis and availability of primary and secondary metabolites including volatile organic compounds (VOC's) is highly variable. In scented rice, aroma volatiles are synthesized in aerial plant parts and deposited in mature grains. There are more than 100 VOCs reported to be responsible for flavor in basmati rice. It will be interesting to keep track of aroma volatiles across the developmental stages in scented rice. Therefore, the aroma volatiles contributing in aroma with special reference to the major compound 2 acetyl-1-pyrroline (2AP) were screened at seven developmental stages in scented rice cultivars Basmati-370 and Ambemohar-157 along with non-scented rice cultivar IR-64 as a control following HS-SPME-GC-MS method. In addition, the expression levels of key genes and precursor levels involved in 2AP biosynthesis were studied.

RESULTS

The study indicated that volatilome of scented rice cultivars is more complex than non-scented rice cultivar. N-heterocyclic class was the major distinguishing class between scented from non-scented rice. A total of 14 compounds including, 2AP were detected specifically in scented rice cultivars. Maximum number of compounds were synthesized at seedling stage and decreased gradually at reproductive and maturity. The seedling stage is an active phase of development where maximum number green leaf volatiles were synthesized which are known to act as defense molecules for protection of young plant parts. Among the 14 odor active compounds (OACs), 10 OACs were accumulated at higher concentrations significantly in scented rice cultivars and contribute in the aroma. 2AP content was highest in mature grains followed by at booting stage. Gene expression analysis revealed that reduced expression of betaine aldehyde dehydrogenase 2 (badh2) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and elevated level of triose phosphate isomerase (TPI) and Δ1-Pyrolline-5-carboxylic acid synthetase (P5CS) transcript enhances 2AP accumulation.

CONCLUSIONS

Most diverse compounds were synthesized at seedling stage and OACs were accumulated more at flowering followed by seedling stage. Distinct accumulation pattern exists for 2AP and other aroma volatiles at various developmental stages. The study revealed the mechanism of 2AP accumulation such that 2AP in mature grains might be transported from leaves and stem sheath and accumulation takes place in grains.

Functional Characterization of 9-/13-LOXs in Rice and Silencing Their Expressions to Improve Grain Qualities

Lipoxygenases (LOXs) are involved in oxidative rancidity and render rice unsuitable for human consumption. Here, RNA interference- (RNAi-) induced gene expression inhibition was used to analyze the functions of the bran/seed-specific LOXs in rice. r9-LOX1 and L-2 (9-LOX category) were the candidate genes expressing a bran/seed-specific LOX, while RCI-1 was (13-LOX category) a plastid-specific LOX. Real-time PCR showed that three LOXs were cultivar/tissue specific expression on a certain level. r9-LOX1 and L-2 were generally much higher in active bran/seed than in stabilized bran, mature seed, and regenerated plant. RCI-1 was barely expressed in seed. In transgenic lines, r9-LOX1, as well as L-2, expression was dramatically downregulated, compared to the nontransgenic controls. SPME/GC-MS analysis of r9-LOX1 RNAi transgenic lines showed 74.33% decrease in nonanal content (formed during oxidation of linoleic acid by lipoxygenase), but 388.24% increase in acetic acid and 184.84% hexanal (direct products of 13-LOX). These results indicate that r9-LOX1 positively regulates the amount of nonanal but negatively regulates acetic acid and hexanal. The negative regulation may be due to a mechanism of negative feedback between LOX family members. The information will help comprehensively understand the function of the bran/seed-specific LOXs, r9-LOX1, and improve the storage quality in the future.

TALEN-Based Mutagenesis of Lipoxygenase LOX3 Enhances the Storage Tolerance of Rice (Oryza sativa) Seeds

The deterioration of rice grain reduces the quality of rice, resulting in serious economic losses for farmers. Lipoxygenases (LOXs) catalyze the dioxygenation of polyunsaturated fatty acids with at least one cis,cis-1,4-pentadiene to form hydroperoxide, which is a major factor influencing seed longevity and viability. Recently, genome editing, an essential tool employed in reverse genetics, has been used experimentally to investigate basic plant biology or to modify crop plants for the improvement of important agricultural traits. In this study, we performed targeted mutagenesis in rice using transcription activator-like effector nucleases (TALENs) to improve seed storability. A modified ligation-independent cloning method (LIC) was employed to allow for the quick and efficient directional insertion of TALEN monomer modules into destination vectors used in plants. We demonstrated the feasibility and flexibility of the technology by developing a set of modular vectors for genome editing. After construction and validation, the TALEN pairs were used to create stable transgenic rice lines via Agrobacterium-mediated transformation. One heterozygous mutant (4%) was recovered from 25 transgenic NPTII-resistant lines, and the mutation was transmitted to the next generation. Further molecular and protein level experiments verified LOX3 deficiency and demonstrated the improvement of seed storability. Our work provides a flexible genome editing tool for improving important agronomic traits, as well as direct evidence that Lox3 has only a limited impact on seed longevity.

Marker-assisted breeding of a LOX-3-null rice line with improved storability and resistance to preharvest sprouting

Breakage of the tight linkage between rice seed lipoxygenase - 3 and easy preharvest sprouting trait led to breeding of lines with few stale flavors after long storage and desirable preharvest sprouting resistance. Lipoxygenase-3 (LOX-3) is involved in the production of volatile constituents in stored rice, and the development of stale flavor is delayed in LOX-3 null rice. In the process of breeding new LOX-3-null lines with long storability, we found a close association between LOX-3 and preharvest sprouting resistance. To determine whether this relationship was due to the tight linkage of two genes or the pleiotropic effect of LOX-3, we performed marker-assisted selection using a BC3F3 population derived from crosses between LOX-3-present/preharvest sprouting-resistant lines and LOX-3-null/preharvest susceptible lines. In one individual, a recombination event occurred 13 kb downstream of LOX-3 (RM15750) and a significant quantitative trait locus, namely qPHS3, for easy preharvest sprouting trait (LOD = 10.4) was detected in an 842-kb region between RM15711 and RM15768. Using BC3F4 and BC3F5 populations, we succeeded in selecting LOX-3-absent and preharvest sprouting-resistant lines with only a 393-kb introgressed chromosome segment from the donor line for LOX-3-null at the LOX-3 locus on chromosome 3. This result indicated that the LOX-3 gene and the locus affecting preharvest sprouting are distinct. The selected line was named 'Hokuriku 244'. Sensory testing of rice grains with and without LOX-3 confirmed that stale flavor production in LOX-3-null rice during storage was lower than in normal LOX-3 rice. These results indicated that rice varieties with little stale flavor after long storage and preharvest sprouting resistance had been selected.

Down-regulation of lipoxygenase gene reduces degradation of carotenoids of golden rice during storage

Down-regulation of lipoxygenase enzyme activity reduces degradation of carotenoids of bio-fortified rice seeds which would be an effective tool to reduce huge post-harvest and economic losses of bio-fortified rice seeds during storage. Bio-fortified provitamin A-enriched rice line (golden rice) expressing higher amounts of β-carotene in the rice endosperm provides vitamin A for human health. However, it is already reported that degradation of carotenoids during storage is a major problem. The gene responsible for degradation of carotenoids during storage has remained largely unexplored till now. In our previous study, it has been shown that r9-LOX1 gene is responsible for rice seed quality deterioration. In the present study, we attempted to investigate if r9-LOX1 gene has any role in degradation of carotenoids in rice seeds during storage. To establish our hypothesis, the endogenous lipoxygenase (LOX) activity of high-carotenoid golden indica rice seed was silenced by RNAi technology using aleurone layer and embryo-specific Oleosin-18 promoter. To check the storage stability, LOX enzyme down-regulated high-carotenoid T3 transgenic rice seeds were subjected to artificial aging treatment. The results obtained from biochemical assays (MDA, ROS) also indicated that after artificial aging, the deterioration of LOX-RNAi lines was considerably lower compared to β-carotene-enriched transgenic rice which had higher LOX activity in comparison to LOX-RNAi lines. Furthermore, it was also observed by HPLC analysis that down-regulation of LOX gene activity decreases co-oxidation of β-carotene in LOX-RNAi golden rice seeds as compared to the β-carotene-enriched transgenic rice, after artificial aging treatment. Therefore, our study substantially establishes and verifies that LOX is a key enzyme for catalyzing co-oxidation of β-carotene and has a significant role in deterioration of β-carotene levels in the carotenoid-enriched golden rice.

Review of methods for the detection and quantification of adulteration of rice: Basmati as a case study

Rice is a staple and widely grown crop endowed with rich genetic diversity. As it is difficult to differentiate seeds of various rice varieties based on visual observation accurately, the harvested seeds and subsequent processed products are highly prone to adulteration with look-alike and low quality seeds by the dishonest traders. To protect the interests of importing countries and consumers, several methods have been employed over the last few decades for unambiguous discrimination of cultivars, accurate quantification of the adulterants, and for determination of cultivated geographical area. With recent advances in biotechnology, DNA based techniques evolved rapidly and proved successful over conventional non-DNA based methods to purge the problem of adulteration at commercial level. In the current review, we made an attempt to summarize the existing methods of adulteration detection and quantification in a comprehensive manner by providing Basmati as a case study to enable the traders to arrive at a quick resolution in choosing the apt method to eliminate the adulteration practice in the global rice industry.

Antisense suppression of LOX3 gene expression in rice endosperm enhances seed longevity

Lipid peroxidation plays a major role in seed longevity and viability. In rice grains, lipid peroxidation is catalyzed by the enzyme lipoxygenase 3 (LOX3). Previous reports showed that grain from the rice variety DawDam in which the LOX3 gene was deleted had less stale flavour after grain storage than normal rice. The molecular mechanism by which LOX3 expression is regulated during endosperm development remains unclear. In this study, we expressed a LOX3 antisense construct in transgenic rice (Oryza sativa L.) plants to down-regulate LOX3 expression in rice endosperm. The transgenic plants exhibited a marked decrease in LOX mRNA levels, normal phenotypes and a normal life cycle. We showed that LOX3 activity and its ability to produce 9-hydroperoxyoctadecadienoic acid (9-HPOD) from linoleic acid were significantly lower in transgenic seeds than in wild-type seeds by measuring the ultraviolet absorption of 9-HPOD at 234 nm and by high-performance liquid chromatography. The suppression of LOX3 expression in rice endosperm increased grain storability. The germination rate of TS-91 (antisense LOX3 transgenic line) was much higher than the WT (29% higher after artificial ageing for 21 days, and 40% higher after natural ageing for 12 months). To our knowledge, this is the first report to demonstrate that decreased LOX3 expression can preserve rice grain quality during storage with no impact on grain yield, suggesting potential applications in agricultural production.

Chemical compositions of the volatile extracts from seeds of Dendranthema nankingense and Borago officinalis

Volatile extracts from the seeds of Dendranthema nankingense Hand.-Mazz. and Borago officinalis L. were prepared using simultaneous distillation and extraction, and analyzed with gas chromatography–mass spectrometry on two capillary gas chromatography columns of different polarity. Ninety-five volatile compounds were identified in D. nankingense seeds, with hexanal, benzeneacetaldehyde, borneol, (−)-camphor, and 3-methyl-1-butanol being the predominant species. Sixty-five volatile compounds were identified in B. officinalis seeds, with 2-pentanone, 2,3-dihydro-benzofuran, 3-methyl butanal, and hexanal being the most abundant species. Thirty-three compounds, including short-chain aliphatic aldehydes, alcohols, and ketones, were common to both seeds. The volatile composition of both seeds varied significantly depending on their respective origins. The volatile terpenoids borneol and (−)-camphor could be key bioactive contributors to the characteristic flavor and cooling effects of D. nankingense. For the first time, coumaran was identified as an abundant species in plant seeds.

Effect of roasting on the volatile constituents of Trichosanthes kirilowii seeds

Roasted Trichosanthes kirilowii seeds have much more intense flavor than the raw seeds, and are commonly used as food and in the preparations of many medicinal formulations. Volatile constituents in the raw and roasted T. kirilowii seeds were separated by simultaneous distillation and extraction, and analyzed by gas chromatography–mass spectrometry on two capillary gas chromatography columns of different polarities (DB-WAX and HP-1). A total of 40 volatile compounds were identified in the raw seeds, with pentanal, 2-pentanol, styrene, (Z)-2-heptenal, (+)-calarene, and α-muurolene being the predominant compounds; 40 volatile compounds were also identified in the roasted seeds, with 3-methylbutanal, ethanol, 2-butanol, 2,3-butanediol, (E,E)-2,4-nonadienal, and 2-isopropyl-5-methyl-9-methylene-bicyclo[4.4.0]dec-1-ene being the most abundant compounds. A total of 15 compounds, mostly aldehydes, were common in both seeds. Roasting of T. kirilowii seeds resulted in a significant decrease in the levels of sesquiterpenes and short-chain aliphatic aldehydes. By contrast, high concentrations of 3-methylbutanal, ethanol, 2-butanol, and alkyl pyrazines were generated, which was responsible for the unique flavor of the roasted seeds. The study results may be useful for optimizing the roasting process and oil processing of T. kirilowii seeds.

Production of high oleic rice grains by suppressing the expression of the OsFAD2-1 gene

The composition of rice (Oryza sativa L.) grain fatty acids (18% palmitic acid, 36% oleic acid and 37% linoleic acid) is suboptimal for rice storage and utilisation of rice bran oil as food grade oil or a source of biodiesel. Genetic manipulation of fatty acid composition in rice bran oil to increase oleic acid levels at the expense of linoleic acid and palmitic acid would not only add extra value to the rice, but also enhance health benefits for consumers. Four putative rice microsomal Δ12-fatty acid desaturase (OsFAD2) genes were identified as potentially important target genes to achieve this improvement. Reverse transcription-PCR analysis indicated that OsFAD2-1 was the most highly expressed gene in rice grains. RNA interference (RNAi) suppression of the expression of OsFAD2-1 resulted in an increase of oleic acid and a reduction of linoleic and palmitic acids in T3 grains. The research here showed that in the rice grains, the OsFAD2-1 enzyme was an effective target for raising oleic acid levels at the expense of the oxidatively unstable linoleic acid and the cholesterol-raising palmitic acid.

De-submergence responses of antioxidative defense systems in two wetland plants having escape and quiescence strategies

Fast recovery after de-submergence requires efficient protection against oxidative injuries. We investigated whether de-submergence responses of antioxidant systems differ in two wetland plants, Alternanthera philoxeroides and Hemarthria altissima, characterized by 'escape' and 'quiescence' strategies of flood tolerance, respectively. The antioxidant capacity was assessed in the two species during 10d of recovery following 20d of complete submergence (low light+low O(2)) or severe shading (low light+ambient O(2)). The activities of superoxide dismutase and catalase were measured in leaf and root tissues, along with the concentrations of reduced ascorbate, malondialdehyde, and acetaldehyde. In addition, formation of superoxide (O(2)(-)) and hydrogen peroxide (H(2)O(2)) was detected in leaves by chemical staining. Following de-submergence, plants of A. philoxeroides showed a transient burst of acetaldehyde, while the concentration of acetaldehyde increased slowly and stayed high in leaves of H. altissima. In leaves of A. philoxeroides, the variations in O(2)(-) and H(2)O(2) correlated with the levels of light and O(2), respectively, whereas neither of the two reactive oxygen species was detected in H. altissima. For A. philoxeroides, the antioxidant capacities changed mainly in leaves during the recovery. For H. altissima, changes in reduced ascorbate were found in leaves and those of antioxidant enzyme activities in roots. De-submergence caused some lipid peroxidation in leaves of both species. We conclude that de-submergence responses of the detoxification systems differ between A. philoxeroides and H. altissima, especially in leaves. Dynamic changes were found in A. philoxeroides (having the escape strategy), as opposed to little or slow changes in H. altissima (having the quiescence strategy). Whereas the antioxidant capacities are often strongly influenced by light environments, the toxic compounds and lipid peroxidation indicate harmful effects of changing O(2) concentration which accompanies submergence and de-submergence.

LOX genes in blast fungus (Magnaporthe grisea) resistance in rice

Plant Lipoxygenases (LOX) are known to play major role in plant immunity by providing front-line defense against pathogen-induced injury. To verify this, we isolated a full-length OsLOX3 gene and also 12 OsLOX cDNA clones from Oryza sativa indica (cultivar Pusa Basmati 1). We have examined the role played by LOXs in plant development and during attack by blast pathogen Magnaporthe grisea. Gene expression, promoter region analysis, and biochemical and protein structure analysis of isolated OsLOX3 revealed significant homology with LOX super family. Protein sequence comparison of OsLOXs revealed high levels of homology when compared with japonica rice (up to100%) and Arabidopsis (up to 64%). Isolated LOX3 gene and 12 OsLOX cDNAs contained the catalytic LOX domains much required for oxygen binding and synthesis of oxylipins. Amino acid composition, protein secondary structure, and promoter region analysis (with abundance of motifs CGTCA and TGACG) support the role of OsLOX3 gene in providing resistance to diseases in rice plants. OsLOX3 gene expression analysis of root, shoot, flag leaf, and developing and mature seed revealed organ specific patterns during rice plant development and gave evidence to association between tissue location and physiological roles played by individual OsLOXs. Increased defense activity of oxylipins was observed as demonstrated by PCR amplification of OsLOX3 gene and upon inoculation with virulent strains of M. grisea and ectopic application of methyl jasmonate in the injured leaf tissue in adult rice plants.

Electrophysiological and behavioral activity of (E)-2-hexenal in the granary weevil and its application in food packaging

The purpose of this work was to develop a biodegradable carrier material to control insect pests in cereal products. To this aim, (E)-2-hexenal was used, being a natural compound with antimicrobial activity that is also commonly adopted as a flavoring agent. Three coating layers of polycaprolactone (PCL) were spread onto the internal side of a paperboard carton, the first being the active coating containing (E)-2-hexenal. The antennal sensitivity of Sitophilus granarius to a broad range of doses of (E)-2-hexenal was first demonstrated. Next, the ability of different concentrations of this compound to disrupt the orientation of adult S. granarius beetles to odors of intact wheat kernels was established in a two-choice pitfall bioassay. In addition, invasion tests were carried out over an 8-week period to highlight the effects of the biobased repellent packaging and their potential persistence. The results demonstrated that during the entire monitoring period, the percentage of S. granarius adults found in cartons coated with (E)-2-hexenal-loaded multilayer PCL was about 10 % of the total number of insects used in the bioassay, very low compared with the respective control samples, thus assessing both the effectiveness and persistence of the repellent system developed. Although the infestation level of treated packages was reduced relative to the infestation levels in the controls, any infestation of food packages is unacceptable to consumers, so further tests are required to determine whether infestation can be completely prevented using (E)-2-hexenal.

Effects of lipase, lipoxygenase, peroxidase and free fatty acids on volatile compound found in boiled buckwheat noodles

BACKGROUND

Relationships between buckwheat (Fagopyrum esculentum Moench) flour lipase, lipoxygenase and peroxidase activity, along with levels of individual free fatty acids (FFAs) and levels of headspace volatile compounds of boiled buckwheat noodles, were investigated for 12 different buckwheat varieties. Enzyme activities and FFA levels in flour were correlated with their respective varietal arrays of boiled noodle headspace volatile compounds, measured by gas chromatography-mass spectrometry.

RESULTS

The volatiles hexanal, tentative butanal, tentative 3-methylbutanal and tentative 2-methylbutanal showed significant positive correlation with one another, indicating that they may be generated through similar mechanisms. These important volatile components of buckwheat flavor were also positively correlated with lipase and/or peroxidase activity, indicating that enzymatic reactions are important in flavor generation in boiled buckwheat noodles. On the other hand, pentanal, which showed no significant correlation with any enzyme activity, showed a significant positive correlation to the levels of C18:2 and C18:3 FFAs, suggesting the existence of a 'non-enzymatic' and/or 'uncertain enzymatic pathway' for flavor generation in boiled buckwheat noodles.

CONCLUSION

Lipase and peroxidase in buckwheat flour are important for flavor generation of boiled buckwheat noodles. This information is important for increasing desirable flavor of buckwheat products as well as for selecting varieties with improved flavor.