Viability and bar expression are negatively correlated in Oregon Wolfe Barley Dominant hybrids

Application of a novel phosphinothricin N-acetyltransferase (RePAT) gene in developing glufosinate-resistant rice

Currently, only few glufosinate-resistant genes are available for commercial application. Thus, developing novel glufosinate-resistant genes with commercial feasibility is extremely important and urgent for agricultural production. In this study, we transferred a newly isolated RePAT gene into a japonica rice variety Zhonghua11, resulting in a large number of independent T0 transgenic plants, most of which grew normally under high-concentration glufosinate treatment. Four transgenic plants with one intact RePAT expression cassette integrated into the intergenic region were selected. Agronomic performances of their T2 progenies were investigated, and the results suggested that the expression of RePAT had no adverse effect on the agronomic performance. Definite glufosinate resistance of the selected transgenic plants was further confirmed to be related to the expression of RePAT by assay on the medium and qRT-PCR. The inheritance and expression of RePAT in two transgenic plants were confirmed to be stable. Finally, the two-year field assay of glufosinate resistance suggested that the agronomic performance of the transgenic plant (PAT11) was not affected by high dosage of glufosinate (5000 g/ha). Collectively, our study proves the high resistance of a novel gene RePAT to glufosinate and provides a glufosiante-resistant rice variety with agricultural application potential.

Field performance of transgenic citrus trees: assessment of the long-term expression of uidA and nptII transgenes and its impact on relevant agronomic and phenotypic characteristics

BACKGROUND

The future of genetic transformation as a tool for the improvement of fruit trees depends on the development of proper systems for the assessment of unintended effects in field-grown GM lines. In this study, we used eight transgenic lines of two different citrus types (sweet orange and citrange) transformed with the marker genes β-glucuronidase (uidA) and neomycin phosphotransferase II (nptII) as model systems to study for the first time in citrus the long-term stability of transgene expression and whether transgene-derived pleiotropic effects occur with regard to the morphology, development and fruit quality of orchard-grown GM citrus trees.

RESULTS

The stability of the integration and expression of the transgenes was confirmed in 7-year-old, orchard-grown transgenic lines by Southern blot analysis and enzymatic assays (GUS and ELISA NPTII), respectively. Little seasonal variation was detected in the expression levels between plants of the same transgenic line in different organs and over the 3 years of analysis, confirming the absence of rearrangements and/or silencing of the transgenes after transferring the plants to field conditions. Comparisons between the GM citrus lines with their non-GM counterparts across the study years showed that the expression of these transgenes did not cause alterations of the main phenotypic and agronomic plant and fruit characteristics. However, when comparisons were performed between diploid and tetraploid transgenic citrange trees and/or between juvenile and mature transgenic sweet orange trees, significant and consistent differences were detected, indicating that factors other than their transgenic nature induced a much higher phenotypic variability.

CONCLUSIONS

Our results indicate that transgene expression in GM citrus remains stable during long-term agricultural cultivation, without causing unexpected effects on crop characteristics. This study also shows that the transgenic citrus trees expressing the selectable marker genes that are most commonly used in citrus transformation were substantially equivalent to the non-transformed controls with regard to their overall agronomic performance, as based on the use of robust and powerful assessment techniques. Therefore, future studies of the possible pleiotropic effects induced by the integration and expression of transgenes in field-grown GM citrus may focus on the newly inserted trait(s) of biotechnological interest.

Selectable marker genes and unintended changes to the plant transcriptome

The intended effect of a selectable marker gene is to confer a novel trait that allows for the selection and recovery of transgenic plants. Unintended effects may also occur as a result of interactions between the selectable marker gene or its regulatory elements and genetic elements at the site of insertion. These are called position effects. Other unintended effects may occur if the selectable marker gene has a range of pleiotropic effects related to the functional and regulatory domains within the coding region or the regulatory elements used to drive expression. Both pleiotropic and position effects may generate unpredictable events depending on the process used for transgenesis and the state of knowledge associated with the selectable marker gene. Although some selectable marker genes, such as the neomycin phosphotransferase type II gene (nptII), have no pleiotropic effects on the transcriptomes of transgenic plants, others, such as the bialaphos resistance gene (bar), have pleiotropic effects. These must be clearly understood and accounted for when evaluating the expression patterns conferred by other co-transforming transgenes under study. The number and kinds of selectable marker genes are large. A detailed understanding of their unintended effects is needed to develop transgenic strategies that will minimize or eliminate unintended and unpredictable changes to plants with newly inserted genes.

The pleiotropic effects of the bar gene and glufosinate on the Arabidopsis transcriptome

The Arabidopsis transcriptome was studied using the Affymetrix Arabidopsis ATH1 GeneChip in wild-type plants and glufosinate-tolerant transgenic plants expressing the bialaphos resistance (bar) gene. Pleiotropic effects were specifically generated in the transcriptomes of transgenic plants by both the bar gene and glufosinate treatments. In the absence of glufosinate, four genes were differentially expressed in the transgenic lines and another 80 genes were differentially expressed in the presence of glufosinate, 29 of which were specific to transgenic plants. In contrast, the number of differentially expressed genes specific to wild-type plants was 194 during the early response at 6 h of glufosinate treatment, and increased to 3711 during the late response at 48 h. Although the wild-type plants undergo extensive transcriptional reprofiling in response to herbicide-induced stress and, finally, plant death, the transgenic plants appear to activate other detoxification processes to offset the toxic effects of the residual herbicide or its derivatives. This study provides the first description of the pleiotropic effects of the bar gene and glufosinate on the plant transcriptome.

The pleiotropic effects of the bar gene and glufosinate on the Arabidopsis transcriptome

The Arabidopsis transcriptome was studied using the Affymetrix Arabidopsis ATH1 GeneChip in wild-type plants and glufosinate-tolerant transgenic plants expressing the bialaphos resistance (bar) gene. Pleiotropic effects were specifically generated in the transcriptomes of transgenic plants by both the bar gene and glufosinate treatments. In the absence of glufosinate, four genes were differentially expressed in the transgenic lines and another 80 genes were differentially expressed in the presence of glufosinate, 29 of which were specific to transgenic plants. In contrast, the number of differentially expressed genes specific to wild-type plants was 194 during the early response at 6 h of glufosinate treatment, and increased to 3711 during the late response at 48 h. Although the wild-type plants undergo extensive transcriptional reprofiling in response to herbicide-induced stress and, finally, plant death, the transgenic plants appear to activate other detoxification processes to offset the toxic effects of the residual herbicide or its derivatives. This study provides the first description of the pleiotropic effects of the bar gene and glufosinate on the plant transcriptome.