Production and phenotypic analysis of rice transgenics with altered levels of pyruvate decarboxylase and alcohol dehydrogenase proteins

Temporal Gene Expression Profiles From Pollination to Seed Maturity in Sorghum Provide Core Candidates for Engineering Seed Traits

Sorghum (Sorghum bicolor (L.) Moench) is a highly nutritional multipurpose millet crop. However, the genetic and molecular regulatory mechanisms governing sorghum grain development and the associated agronomic traits remain unexplored. In this study, we performed a comprehensive transcriptomic analysis of pistils collected 1-2 days before pollination, and developing seeds collected -2, 10, 20 and 30 days after pollination of S. bicolor variety M35-1. Out of 31 337 genes expressed in these stages, 12 804 were differentially expressed in the consecutive stages of seed development. These exhibited 10 dominant expression patterns correlated with the distinct pathways and gene functions. Functional analysis, based on the pathway mapping, transcription factor enrichment and orthology, delineated the key patterns associated with pollination, fertilization, early seed development, grain filling and seed maturation. Furthermore, colocalization with previously reported quantitative trait loci (QTLs) for grain weight/size revealed 48 differentially expressed genes mapping to these QTL regions. Comprehensive literature mining integrated with QTL mapping and expression data shortlisted 25, 17 and 8 core candidates for engineering grain size, starch and protein content, respectively.

Proteomic and Carbonylation Profile Analysis at the Critical Node of Seed Ageing in Oryza sativa

The critical node (CN), which is the transition from the plateau phase to the rapid decreasing phase of seed ageing, is extremely important for seed conservation. Although numerous studies have investigated the oxidative stress during seed ageing, information on the changes in protein abundance at the CN is limited. In this study, we aimed to investigate the abundance and carbonylation patterns of proteins at the CN of seed ageing in rice. The results showed that the germination rate of seeds decreased by less than 20% at the CN; however, the abundance of 112 proteins and the carbonylation levels of 68 proteins markedly changed, indicating oxidative damage. The abundance and activity of mitochondrial, glycolytic, and pentose phosphate pathway proteins were reduced; consequently, this negatively affected energy production and germination. Proteins related to defense, including antioxidant system and heat shock proteins, also reduced in abundance. Overall, energy metabolism was reduced at the CN, leading to a decrease in the antioxidant capacity, whereas seed storage proteins were up-regulated and carbonylated, indicating that the seed had a lower ability to utilize seed storage proteins for germination. Thus, the significant decrease in metabolic activities at the CN might accelerate the loss of seed viability.

Efecto del Anegamiento en la Actividad de la Enzima Alcohol Deshidrogenasa en Raíces de Maracuyá Amarillo Passiflora Edulis var. Flavicarpa

<p><strong>Título en ingles: Effect of Waterlogging on the Alcohol Dehydrogenase Activity in yellow Passion Fruit Roots <em>Passiflora Edulis</em> var. <em>Flavicarpa</em></strong></p><p>Bajo entornos naturales, las plantas de maracuyá amarillo frecuentemente se enfrentan a condiciones de anegamiento, un factor limitante para la producción generalizada de su cultivo, especialmente en tierras bajas inundables. El presente estudio se encargó de identificar la activación de la enzima alcohol deshidrogenasa (ADH) durante la inundación, como un posible mecanismo de sobrevivencia de plántulas de maracuyá amarillo. Se evaluó la actividad de la enzima ADH durante 0, 1, 3, 7, 9 y 14 días de tratamiento con inundación y sin inundación, en raíces de plántulas de maracuyá amarillo de tres meses y medio de germinadas. En las raíces de plántulas de maracuyá amarillo en condiciones de inundación, la actividad de la enzima ADH presentó un aumento significativo respecto a las plántulas en condiciones normales de riego (sin inundación). Esto sugiere que la actividad de la enzima alcohol deshidrogenasa, implicada en el metabolismo anaeróbico, es un posible mecanismo de supervivencia al anegamiento de plántulas de maracuyá amarillo en periodos cortos de inundación.</p>

Rice alcohol dehydrogenase 1 promotes survival and has a major impact on carbohydrate metabolism in the embryo and endosperm when seeds are germinated in partially oxygenated water

BACKGROUND AND AIMS

Rice (Oryza sativa) has the rare ability to germinate and elongate a coleoptile under oxygen-deficient conditions, which include both hypoxia and anoxia. It has previously been shown that ALCOHOL DEHYDROGENASE 1 (ADH1) is required for cell division and cell elongation in the coleoptile of submerged rice seedlings by means of studies using a rice ADH1-deficient mutant, reduced adh activity (rad). The aim of this study was to understand how low ADH1 in rice affects carbohydrate metabolism in the embryo and endosperm, and lactate and alanine synthesis in the embryo during germination and subsequent coleoptile growth in submerged seedlings.

METHODS

Wild-type and rad mutant rice seeds were germinated and grown under complete submergence. At 1, 3, 5 and 7 d after imbibition, the embryo and endosperm were separated and several of their metabolites were measured and compared.

KEY RESULTS

In the rad embryo, the rate of ethanol fermentation was halved, while lactate and alanine concentrations were 2·4- and 5·7- fold higher in the mutant than in the wild type. Glucose and fructose concentrations in the embryos increased with time in the wild type, but not in the rad mutant. The rad mutant endosperm had lower amounts of the α-amylases RAMY1A and RAMY3D, resulting in less starch degradation and lower glucose concentrations.

CONCLUSIONS

These results suggest that ADH1 is essential for sugar metabolism via glycolysis to ethanol fermentation in both the embryo and endosperm. In the endosperm, energy is presumably needed for synthesis of the amylases and for sucrose synthesis in the endosperm, as well as for sugar transport to the embryo.

Role of transgenic plants in agriculture and biopharming

At present, environmental degradation and the consistently growing population are two main problems on the planet earth. Fulfilling the needs of this growing population is quite difficult from the limited arable land available on the globe. Although there are legal, social and political barriers to the utilization of biotechnology, advances in this field have substantially improved agriculture and human life to a great extent. One of the vital tools of biotechnology is genetic engineering (GE) which is used to modify plants, animals and microorganisms according to desired needs. In fact, genetic engineering facilitates the transfer of desired characteristics into other plants which is not possible through conventional plant breeding. A variety of crops have been engineered for enhanced resistance to a multitude of stresses such as herbicides, insecticides, viruses and a combination of biotic and abiotic stresses in different crops including rice, mustard, maize, potato, tomato, etc. Apart from the use of GE in agriculture, it is being extensively employed to modify the plants for enhanced production of vaccines, hormones, etc. Vaccines against certain diseases are certainly available in the market, but most of them are very costly. Developing countries cannot afford the disease control through such cost-intensive vaccines. Alternatively, efforts are being made to produce edible vaccines which are cheap and have many advantages over the commercialized vaccines. Transgenic plants generated for this purpose are capable of expressing recombinant proteins including viral and bacterial antigens and antibodies. Common food plants like banana, tomato, rice, carrot, etc. have been used to produce vaccines against certain diseases like hepatitis B, cholera, HIV, etc. Thus, the up- and down-regulation of desired genes which are used for the modification of plants have a marked role in the improvement of genetic crops. In this review, we have comprehensively discussed the role of genetic engineering in generating transgenic lines/cultivars of different crops with improved nutrient quality, biofuel production, enhanced production of vaccines and antibodies, increased resistance against insects, herbicides, diseases and abiotic stresses as well as the safety measures for their commercialization.

Soluble sugar availability of aerobically germinated barley, oat and rice coleoptiles in anoxia

Physiological and metabolic responses to anoxia were compared for aerobically germinated seedlings of barley (Hordeum vulgare), oat (Avena sativa) and rice (Oryza sativa). Coleoptile growth of barley, oat and rice seedlings was suppressed by a 24 h-anoxic stress, but the growth of the rice coleoptiles was much greater than that of the barley and oat coleoptiles. ATP concentration in the anoxic rice coleoptiles was greater than that in the anoxic barley and oat coleoptiles. Concentrations of ethanol and activity of alcohol dehydrogenase (ADH) in the anoxic rice coleoptiles were also greater than those of the anoxic barley and oat coleoptiles, suggesting that ethanolic fermentation may be more active in the rice coleoptiles than in the barley and oat coleoptiles, where glycolysis and ethanolic fermentation are the main source of ATP production. Soluble sugar concentration in the anoxic rice coleoptiles was greater than that of the anoxic barley and oat coleoptiles. However, α-amylase, which catabolizes reserve starch to soluble sugars, was active in anoxic barley, oat and rice endosperms, and soluble sugar concentration in the anoxic barley, oat and rice endosperms was not significantly different. Therefore, anoxia stress may inhibit soluble sugar transport from the endosperms to the coleoptiles in barley and oat more than in rice. Since the availability of soluble sugar is essential for operation of glycolysis and fermentation in plant cells, ability for sugar transport from the endosperms to the coleoptiles may be one means to distinguish the coleoptile growth of these plant species in anoxia and anoxia tolerance of these plants.

Functional characterization of three water deficit stress-induced genes in tobacco and Arabidopsis: an approach based on gene down regulation

Functional characterization of water deficit stress responsive genes is important to understand their role in stress tolerance. RNAi-based silencing of gene of interest and studying the stress response of knockdown plants under stress can be one of the potential options for assessing functional significance of these genes. Several genes showing higher transcript expression under water deficit stress were cloned earlier from a stress adapted crop species, groundnut. In this study, a few selected gene homologs have been characterized in Nicotiana tabacum and Arabidopsis. Using post transcriptional gene silencing (PTGS) based RNAi approach we developed N. tabacum knockdown lines for three of the genes namely alcohol dehydrogenase (ADH), trans caffeoyl coA-3-O-methyl transferase (CcoAOMT) and flavonol-3-O-glucosyl transferase (F3OGT). By quantitative RT-PCR we demonstrated that the RNAi lines showed significant reduction in target gene transcripts. We followed a stress imposition protocol that allows the plants to experience initial gradual acclimation stress and subsequently severe stress for a definite period. The RNAi knockdown lines generated against ADH and F3OGT, when subjected to water deficit stress showed susceptible symptoms signifying the relevance of these genes under stress. Knockdown of CcoAOMT showed higher chlorophyll degradation and less cell viability upon stress compared to control plants. Further, the Arabidopsis mutant lines clearly showed susceptibility to salinity and water deficit stresses validating relevance of these three genes under abiotic stresses.

Comparative analysis of anoxic coleoptile elongation in rice varieties: relationship between coleoptile length and carbohydrate levels, fermentative metabolism and anaerobic gene expression

Rice (Oryza sativa L.) seeds can germinate under anoxia and can show coleoptile elongation. The anoxic coleoptile is usually longer than aerobic coleoptiles. Although several hypotheses have been proposed to explain the ability of rice to elongate coleoptiles under anoxia, conclusive experimental evidence explaining this physiological trait is lacking. In order to investigate whether metabolic and molecular markers correlate with anoxic coleoptile length, we screened 141 Italian and 23 Sri Lankan rice cultivars for their ability to elongate coleoptiles under anoxia. Differences in anoxic coleoptile length were used to evaluate whether a correlation exists between coleoptile length and biochemical and molecular parameters. The expression of genes coding for glycolytic and fermentative enzymes showed a very low correlation with anoxic coleoptile length. Although differences were found in carbohydrate content between the varieties tested, this parameter also does not appear to be critical in terms of coleoptile elongation. Efficient ethanol fermentation does, however, correlate well with the elongation of coleoptiles under anoxic conditions.

Rice germination and seedling growth in the absence of oxygen

BACKGROUND

Higher plants are aerobic organisms which suffer from the oxygen deficiency imposed by partial or total submergence. However, some plant species have developed strategies to avoid or withstand severe oxygen shortage and, in some cases, the complete absence of oxygen (tissue anoxia) for considerable periods of time.

SCOPE

Rice (Oryza sativa) is one of the few plant species that can tolerate prolonged soil flooding or complete submergence thanks to an array of adaptive mechanisms. These include an ability to elongate submerged shoot organs at faster than normal rates and to develop aerenchyma, allowing the efficient internal transport of oxygen from the re-emerged elongated shoot to submerged parts. However, rice seeds are able to germinate anaerobically by means of coleoptile elongation. This cannot be explained in terms of oxygen transport through an emerged shoot. This review provides an overview of anoxic rice germination that is mediated through coleoptile rather than root emergence.

CONCLUSIONS

Although there is still much to learn about the biochemical and molecular basis of anaerobic rice germination, the ability of rice to maintain an active fermentative metabolism (i.e. by fuelling the glycolytic pathway with readily fermentable carbohydrates) is certainly crucial. The results obtained through microarray-based transcript profiling confirm most of the previous evidence based on single-gene studies and biochemical analysis, and highlight new aspects of the molecular response of the rice coleoptile to anoxia.