Comparative Phenotypic and Agronomic Assessment of Transgenic Potato with 3R-Gene Stack with Complete Resistance to Late Blight Disease

Transgenic potato event Vic.172, expressing three naturally occurring resistance genes (R genes) conferring complete protection against late blight disease, was evaluated for resistance to late blight, phenotypic characterization, and agronomic performance in field conditions at three locations during three seasons in Uganda. These trials were conducted by comparison to the variety Victoria from which Vic.172 derives, using identical fungicide treatment, except when evaluating disease resistance. During all seasons, the transgenic event Vic.172 was confirmed to have complete resistance to late blight disease, whereas Victoria plants were completely dead by 60–80 days after planting. Tubers from Vic.172 were completely resistant to LB after artificial inoculation. The phenotypic characterization included observations of the characteristics and development of the stems, leaves, flowers, and tubers. Differences in phenotypic parameters between Vic.172 and Victoria were not statistically significant across locations and seasons. The agronomic performance observations covered sprouting, emergence, vigor, foliage growth, and yield. Differences in agronomic performance were not statistically significant except for marketable yield in one location under high productivity conditions. However, yield variation across locations and seasons was not statistically significant, but was influenced by the environment. Hence, the results of the comparative assessment of the phenotype and agronomic performance revealed that transgenic event Vic.172 did not present biologically significant differences in comparison to the variety Victoria it derives from.

Impacts of environmental conditions, and allelic variation of cytosolic glutamine synthetase on maize hybrid kernel production

Cytosolic glutamine synthetase (GS1) is the enzyme mainly responsible of ammonium assimilation and reassimilation in maize leaves. The agronomic potential of GS1 in maize kernel production was investigated by examining the impact of an overexpression of the enzyme in the leaf cells. Transgenic hybrids exhibiting a three-fold increase in leaf GS activity were produced and characterized using plants grown in the field. Several independent hybrids overexpressing Gln1-3, a gene encoding cytosolic (GS1), in the leaf and bundle sheath mesophyll cells were grown over five years in different locations. On average, a 3.8% increase in kernel yield was obtained in the transgenic hybrids compared to controls. However, we observed that such an increase was simultaneously dependent upon both the environmental conditions and the transgenic event for a given field trial. Although variable from one environment to another, significant associations were also found between two GS1 genes (Gln1-3 and Gln1-4) polymorphic regions and kernel yield in different locations. We propose that the GS1 enzyme is a potential lead for producing high yielding maize hybrids using either genetic engineering or marker-assisted selection. However, for these hybrids, yield increases will be largely dependent upon the environmental conditions used to grow the plants.

Determination of amino acids and nutritional aspects in transgenic soybean exposed to glyphosate/ Determinação de aminoácidos e aspectos nutricionais na soja transgênica exposta ao glifosato

With the increase of glyphosate tolerant transgenic soybean cultivation areas, this substance has become the main herbicide for this crop, its use may interfere in the metabolism and nutritional aspects of transgenic plants. In this scenario, the objective of this work was to verify the oil, protein, phytate and amino acid concentrations in glyphosate tolerant soybean cultivar. Comparing the averages between oil, protein and total amino acid levels in transgenic soybean exposed and not exposed to glyphosate, it was found that there was no significant difference by Tukey test at 5% probability. In conclusion, the data indicate that although the transgenic event affects some routes, amino acid synthesis was not affected nor in nutritional terms at the glyphosate doses studied.

Development of a Transformable Fast-Flowering Mini-Maize as a Tool for Maize Gene Editing

Maize (Zea mays ssp. mays) is a popular genetic model due to its ease of crossing, well-established toolkits, and its status as a major global food crop. Recent technology developments for precise manipulation of the genome are further impacting both basic biological research and biotechnological application in agriculture. Crop gene editing often requires a process of genetic transformation in which the editing reagents are introduced into plant cells. In maize, this procedure is well-established for a limited number of public lines that are amenable for genetic transformation. Fast-Flowering Mini-Maize (FFMM) lines A and B were recently developed as an open-source tool for maize research by reducing the space requirements and the generation time. Neither line of FFMM were competent for genetic transformation using traditional protocols, a necessity to its status as a complete toolkit for public maize genetic research. Here we report the development of new lines of FFMM that have been bred for amenability to genetic transformation. By hybridizing a transformable maize genotype high Type-II callus parent A (Hi-II A) with line A of FFMM, we introgressed the ability to form embryogenic callus from Hi-II A into the FFMM-A genetic background. Through multiple generations of iterative self-hybridization or doubled-haploid method, we established maize lines that have a strong ability to produce embryogenic callus from immature embryos and maintain resemblance to FFMM-A in flowering time and stature. Using an Agrobacterium-mediated standard transformation method, we successfully introduced the CRISPR-Cas9 reagents into immature embryos and generated transgenic and mutant lines displaying the expected mutant phenotypes and genotypes. The transformation frequencies of the tested genotypes, defined as the numbers of transgenic event producing T1 seeds per 100 infected embryos, ranged from 0 to 17.1%. Approximately 80% of transgenic plants analyzed in this study showed various mutation patterns at the target site. The transformable FFMM line, FFMM-AT, can serve as a useful genetic and genomic resource for the maize community.

Analysis of transcriptomic differences between NK603 maize and near-isogenic varieties using RNA sequencing and RT-qPCR

Background The insertion of a transgene into a plant organism can, in addition to the intended effects, lead to unintended effects in the plants. To uncover such effects, we compared maize grains of two genetically modified varieties containing NK603 (AG8025RR2, AG9045RR2) to their non-transgenic counterparts (AG8025conv, AG9045conv) using high-throughput RNA sequencing. Moreover, in-depth analysis of these data was performed to reveal the biological meaning of detected differences. Results Uniquely mapped reads corresponded to 29,146 and 33,420 counts in the AG8025 and AG9045 varieties, respectively. An analysis using the R-Bioconductor package EdgeR revealed 3534 and 694 DEGs (significant differentially expressed genes) between the varieties AG8025RR2 and AG9045RR2, respectively, and their non-transgenic counterparts. Furthermore, a Deseq2 package revealed 2477 and 440 DEGs between AG8025RR2 and AG9045RR2, respectively, and their counterparts. We were able to confirm the RNA-seq results by the analysis of two randomly selected genes using RT-qPCR (reverse transcription quantitative PCR). PCA and heatmap analysis confirmed a robust data set that differentiates the genotypes even by transgenic event. A detailed analysis of the DEGs was performed by the functional annotation of GO (Gene Ontology), annotation/enrichment analysis of KEGG (Kyoto Encyclopedia of Genes and Genomes) ontologies and functional classification of resulting key genes using the DAVID Bioinformatics Package. Several biological processes and metabolic pathways were found to be significantly different in both variety pairs. Conclusion Overall, our data clearly demonstrate substantial differences between the analyzed transgenic varieties and their non-transgenic counterparts. These differences indicate that several unintended effects have occurred as a result of NK603 integration. Heatmap data imply that most of the transgenic insert effects are variety-dependent. However, identified key genes involved in affected pathways of both variety pairs show that transgenic independent effects cannot be excluded. Further research of different NK603 varieties is necessary to clarify the role of internal and external influences on gene expression. Nevertheless, our study suggests that RNA-seq analysis can be utilized as a tool to characterize unintended genetic effects in transgenic plants and may also be useful in the safety assessment and authorization of genetically modified (GM) plants.

Standardization of PCR and sequencing-based methods for the detection of the presence of CP4 EPSPS gene in Zea mays

With the rise in planting of transgenic cultivars in Brazil as well as worldwide, the demand for legal regulations has increased. The transgenic event MON88017 is often found in maize cultivars marketed in Brazil. The event contains the CP4 EPSPS and cry3Bb1 genes, which encode tolerance to the herbicide glyphosate and resistance to caterpillars, respectively. Globally, methodologies to track transgenic events are mandatory. The objective of this study was to standardize a method based on qualitative PCR and sequencing for detection of the CP4 EPSPS gene in Zea mays. DNA was extracted from three commercial strains of transgenic maize, containing the MON88017 event, as well as conventional maize. Primers were designed for partial detection of the zein and CP4 EPSPS genes. PCR reactions were performed for detection of partial regions of CP4 EPSPS and Zein (as endogenous marker of Z. mays) genes. The three transgenic maize inbred lines tested positive for zein and CP4 EPSPS, and the two conventional strains tested negative for CP4 EPSPS and positive for the Zein gene. To confirm the presence of the genic regions, PCR products were sequenced and showed 100% identity with sequences of Zein and CP4 EPSPS genes deposited in GenBank. Thus, the results of this study suggest the applicability of an ‘in-house’ method for the qualitative detection of CP4 EPSPS in genetically modified maize cultivars.

Influence of Heat Processing on DNA Degradation and PCR-Based Detection of Wild-Type and Transgenic Maize

Reliable detection of genetically modified (GM) maize is significant for food authenticity, labelling, quality, and safety assessment. This study aims to evaluate the factors influencing degradation and polymerase chain reaction (PCR) amplification of DNA from the wild type and transgenic maize (events Bt-176 and MON810) during thermal treatment at 100°C and 121°C. A new PCR method was developed targeting the Cry1Ab gene to detect insect-resistant GM plants. The yield of genomic DNAs extracted by the DNeasy plant mini kit dramatically decreased while DNAs obtained by cetyltrimethyl ammonium bromide- (CTAB-) based method did not show any visible changes in the yield by the time of processing. Treatment at 100°C did not significantly affect either genomic DNAs or amplicons. Heating at 121°C induced time-dependent degradation of genomic DNAs and exogenous Cry1Ab gene; however, it did not have any considerable influence on the exogenous 141 bp amplicons or endogenous amplicons in the range of 102 bp to 226 bp with the exception of the event MON810 extracted by the DNeasy plant mini kit. More yield was observed at 226 bp than 140 bp fragment of the invertase gene. The 141 bp fragment of the transgenic CaMV 35S promoter exhibited the highest thermal stability of all the examined amplicons. Analysis of foodstuffs demonstrated 102 bp amplicons specific for the zein gene as the effective marker to detect maize in the processed foods. The obtained results demonstrate that PCR-based detection of the wild type and transgenic maize is dependent on the combination of different parameters of crucial factors such as temperature and duration of exposure, transgenic event, DNA extraction method, DNA marker, and size and location of amplicons.