Metabolomic changes in grains of well-watered and drought-stressed transgenic rice.

BACKGROUND: Drought induces a number of physiological and biochemical responses in cereals. This study was designed to examine the metabolite changes in grains of drought-tolerant transgenic rice (Oryza sativa L.) that overexpresses AtCYP78A7 encoding cytochrome P450 protein using proton nuclear magnetic resonance ((1)H-NMR) and gas chromatography/mass spectrometry. RESULTS: Principal component analysis showed that the (1)H-NMR-based profile was clearly separated by soil water status of well-watered and water-deficit. A discrimination of metabolites between transgenic and non-transgenic grains appeared under both watering regimes. Variations in the levels of amino acids and sugars led to the discrimination of metabolites among genotypes. In particular, drought significantly enhanced the levels of γ-aminobutyric acid (GABA, 244.6%), fructose (155.7%), glucose (211.0%), glycerol (57.2%), glycine (65.8%) and aminoethanol (192.4%) in the transgenic grains compared with the non-transgenic control grains. CONCLUSION: These changes in amounts of metabolites may assist in improving drought tolerance in transgenic rice by playing crucial roles in stress-responsive pathways including GABA biosynthesis, sucrose metabolism and antioxidant defenses.

Ecological network analysis reveals distinctive microbial modules associated with heavy metal contamination of abandoned mine soils in Korea.

Heavy metal pollution in soil around abandoned mine sites is one of the most critical environmental issues worldwide. Soil microbes form complex communities and perform ecological functions individually or in cooperation with other organisms to adapt to harsh environments. In this study, we investigated the distribution patterns of bacterial and fungal communities in non-contaminated and heavy metal-contaminated soil of the abandoned Samkwang mine in Korea to explore microbial interaction mechanisms and their modular structures. As expected, the bacterial and fungal community structures showed large differences depending on the degree of heavy metal contamination. The microbial network was divided into three modules based on the levels of heavy metal pollution: heavy metal-tolerant (HM-Tol), heavy metal-mid-tolerant (HM-mTol), and heavy metal-sensitive (HM-Sens) modules. Taxonomically, microbes assigned to Vicinamibacterales, Pedosphaeraceae, Nitrosomonadaceae, and Gemmatimonadales were the major groups constituting the HM-Tol module. Among the detected heavy metals (As, Pb, Cd, Cu, and Zn), copper concentrations played a key role in the formation of the HM-Tol module. In addition, filamentous fungi (Fusarium and Mortierella) showed potential interactions with bacteria (Nitrosomonadaceae) that could contribute to module stability in heavy metal-contaminated areas. Overall, heavy metal contamination was accompanied by distinct microbial communities, which could participate in the bioremediation of heavy metals. Analysis of the microbial interactions among bacteria and fungi in the presence of heavy metals could provide fundamental information for developing bioremediation mechanisms for the recovery of heavy metal-contaminated soil.

Compositional differences in hybrids between protoporphyrinogen IX oxidase (PPO)-inhibiting herbicide-resistant transgenic rice and weedy rice accessions.

We characterized the metabolites in grains of transgenic protoporphyrinogen IX oxidase-inhibiting herbicide-resistant rice and weedy accessions using GC-MS and examined whether the chemical composition of their hybrids differed from that of the parents. We found that the metabolite profiles of transgenic rice and weedy rice were clearly separated. Although the metabolite profiles of F2 progeny were partially separated from their parents, zygosity did not affect the profiles. The F2 progeny had similar or intermediate levels of most major nutritional components compared with their parents. However, levels of galactopyranose, trehalose, xylofuranose, mannitol, and benzoic acid were higher in the F2 progeny. Some fatty acids and organic acids also showed prominent quantitative differences between the F2 progeny and the parents. Changes in the metabolite levels of transgenic crop-weed hybrids compared to their parents might influence not only the ecological consequences of the hybrids, but also the nutritional quality and food safety.

Performance of hybrids between abiotic stress-tolerant transgenic rice and its weedy relatives under water-stressed conditions.

Gene transfer from transgenic crops to their weedy relatives may introduce undesired ecological consequences that can increase the fitness and invasiveness of weedy populations. Here, we examined the rate of gene flow from abiotic stress-tolerant transgenic rice that over-express AtCYP78A7, a gene encoding cytochrome P450 protein, to six weedy rice accessions and compared the phenotypic performance and drought tolerance of their hybrids over generations. The rate of transgene flow from AtCYP78A7-overexpressing transgenic to weedy rice varied between 0% and 0.0396%. F1 hybrids containing AtCYP78A7 were significantly taller and heavier, but the percentage of ripened grains, grain numbers and weight per plant were significantly lower than their transgenic and weedy parents. The homozygous and hemizygous F2 progeny showed higher tolerance to drought stress than the nullizygous F2 progeny, as indicated by leaf rolling scores. Shoot growth of nullizygous F3 progeny was significantly greater than weedy rice under water-deficient conditions in a rainout shelter, however, that of homozygous F3 progeny was similar to weedy rice, indicating the cost of continuous expression of transgene. Our findings imply that gene flow from AtCYP78A7-overexpressing transgenic to weedy rice might increase drought tolerance as shown in the pot experiment, however, increased fitness under stressed conditions in the field were not observed for hybrid progeny containing transgenes.

Temperature regulates tuber-inducing lipoxygenase-derived metabolites in potato (Solanum tuberosum).

Temperature is one of the major environmental factors affecting potato tuberization. It has been suggested that lipoxygenase (LOX) mediates between temperature and tuber induction. In this study, the contents of the LOX-derived metabolites hydroperoxylinolenic acid (HPOT), jasmonic acid (JA), tuberonic acid (TA) and tuberonic acid glucoside (TAG) were analyzed in leaves of potatoes growing at different temperatures. At low, tuber-inducing temperature, endogenous levels of JA, TA and TAG rise, indicating their crucial role in tuber induction. The concentration of 13(S)-HPOT seems not to be directly affected by temperature. Instead, the molecule has only a short half-life in leaves and is readily metabolized.

Salinity affects metabolomic profiles of different trophic levels in a food chain.

Salinization is one of the most important abiotic stressors in an ecosystem. To examine how exposing a host plant to excess salt affects the consequent performance and metabolism of insects in a food chain, we determined the life history traits and the metabolite profiles in rice (Oryza sativa), the herbivore Sitobion avenae, and its predator Harmonia axyridis. When compared with performance under normal (non-stressed) conditions, exposing plants to 50mM NaCl significantly delayed the timing of development for S. avenae fed on rice and H. axyridis and also reduced the body mass of the latter. Our GC-MS-based analysis revealed clear differences in metabolite profiles between trophic levels or treatment conditions. Salinity apparently increased the levels of main components in rice, but decreased levels of major components in S. avenae and H. axyridis. In addition, 16 metabolites showed salinity-related contrasts in this trophic interaction for our rice-S. avenae-H. axyridis system. Salinity impeded the accumulation of metabolites, especially several sugars, amino acids, organic acids, and fatty acids in both insects, a response that was possibly associated with the negative impacts on their growth and reproduction under stress conditions.

Inhibition of stem elongation in spinach by theobroxide.

In the current study, we investigated the influences of theobroxide on stem elongation in spinach (Spinacia oleracea). Our results showed that stem elongation and flower formation were inhibited by spraying spinach plants with theobroxide under inductive, long day conditions (16 h light/8 h dark), while application of exogenous applied GA3 prevented the effect of theobroxide. Quantitative analysis showed that theobroxide suppressed GA1 biosynthesis, whereas the endogenous content of jasmonic acid was unchanged. However, under short day conditions (10 h light/14 h dark), there were no differences in stem length between treated and untreated plants. These results suggest that the inhibition of stem elongation by theobroxide is probably due to the suppression of gibberellin biosynthesis.

Comparative analysis of chemical compositions between non-transgenic soybean seeds and those from plants over-expressing AtJMT, the gene for jasmonic acid carboxyl methyltransferase.

Transgenic overexpression of the Arabidopsis gene for jasmonic acid carboxyl methyltransferase (AtJMT) is involved in regulating jasmonate-related plant responses. To examine its role in the compositional profile of soybean (Glycine max), we compared the seeds from field-grown plants that over-express AtJMT with those of the non-transgenic, wild-type (WT) counterpart. Our analysis of chemical compositions included proximates, amino acids, fatty acids, isoflavones, and antinutrients. Overexpression of AtJMT in the seeds resulted in decreased amounts of tryptophan, palmitic acid, linolenic acid, and stachyose, but increased levels of gadoleic acid and genistein. In particular, seeds from the transgenic soybeans contained 120.0-130.5% more genistein and 60.5-82.1% less stachyose than the WT. A separate evaluation of ingredient values showed that all were within the reference ranges reported for commercially available soybeans, thereby demonstrating the substantial equivalence of these transgenic and non-transgenic seeds.

Drought stress-induced compositional changes in tolerant transgenic rice and its wild type.

Comparing well-watered versus deficit conditions, we evaluated the chemical composition of grains harvested from wild-type (WT) and drought-tolerant, transgenic rice (Oryza sativa L.). The latter had been developed by inserting AtCYP78A7, which encodes a cytochrome P450 protein. Two transgenic Lines, '10B-5' and '18A-4', and the 'Hwayoung' WT were grown under a rainout shelter. After the harvested grains were polished, their levels of key components, including proximates, amino acids, fatty acids, minerals and vitamins were analysed to determine the effect of watering system and genotype. Drought treatment significantly influenced the levels of some nutritional components in both transgenic and WT grains. In particular, the amounts of lignoceric acid and copper in the WT decreased by 12.6% and 39.5%, respectively, by drought stress, whereas those of copper and potassium in the transgenics rose by 88.1-113.3% and 10.4-11.9%, respectively, under water-deficit conditions.

Interactions among LOX metabolites regulate temperature-mediated flower bud formation in morning glory (Pharbitis nil).

We examined the relationship between temperature (15-35°C) and flower induction as it is influenced by linolenic acid (LA) cascade products, lipoxygenase (LOX; EC 1.13.11.12), allene oxide synthase (AOS; EC 4.2.1.92), and allene oxide cyclase (AOC; EC 5.3.99.6) generated in morning glory (Pharbitis nil Choisy). The maximum amount of LOX protein was detected when plants were grown at 30°C, whereas endogenous AOS and AOC proteins were markedly accumulated at 15°C. Although both test levels of 9(S)- and 13(S)-hydroperoxy linolenic acid (HPOT) showed similar temperature dependencies, reflecting the profile of LOX, the relative amount of 13(S)-HPOT was much higher than that of 9(S)-HPOT, regardless of temperature regime. This implied a faster reaction pathway to 9,10-α-ketol octadecadienoic acid (KODA) in the LA cascade. In the 13(S)-HPOT pathway, the highest level of endogenous jasmonic acid (JA) was observed at 15°C. Our results suggest that at a high temperature (30°C), 9(S)-HPOT may be readily metabolized into KODA to promote flower bud formation. By contrast, at a low temperature, high levels of AOS and AOC result in an accumulation of JA that inhibits this developmental process. Accordingly, depending on the growing temperature, flower bud formation in P. nil is possibly regulated by the interactions among LOX metabolites, with KODA serving as a promoter and JA as an inhibitor.