Expression and inheritance pattern of two foreign genes in petunia

Overexpression of the oil palm (Elaeis guineensis Jacq.) TAPETUM DEVELOPMENT1-like Eg707 in rice affects cell division and differentiation and reduces fertility

The functional analysis of the TAPETUM DEVELOPMENT1-like analog Eg707 of oil palm was carried out in rice by over-expressing Eg707 under the control of a double cauliflower mosaic virus 35S promoter. Ectopic expression of Eg707 in rice induced dark green and matured compact brownish calli compared to pale wild type and negative control calli. Regenerated transgenic rice plants exhibited a reduction in organ size and plant height, rolled, erect leaves, less tillers, increased chlorophyll content, and reduced fertility with smaller green seeds. At the molecular level Eg707 overexpression caused an increase in the transcription of SAPK9, a SnRK2 protein kinase family member that is activated by ABA and hyperosmotic stress. Together, the results show that ectopic Eg707 expression influences cell division and differentiation, presumably via altered hormone homeostasis.

Ovary-drip transformation: a simple method for directly generating vector- and marker-free transgenic maize (Zea mays L.) with a linear GFP cassette transformation

The presence of selectable marker genes and vector backbone sequences has affected the safe assessment of transgenic plants. In this study, the ovary-drip method for directly generating vector- and selectable marker-free transgenic plants was described, by which maize was transformed with a linear GFP cassette (Ubi-GFP-nos). The key features of this method center on the complete removal of the styles and the subsequent application of a DNA solution directly to the ovaries. The movement of the exogenous DNA was monitored using fluorescein isothiocyanate-labeled DNA, which showed that the time taken by the exogenous DNA to enter the ovaries was shortened compared to that of the pollen-tube pathway. This led to an improved transformation frequency of 3.38% compared to 0.86% for the pollen-tube pathway as determined by PCR analysis. The use of 0.05% surfactant Silwet L-77 + 5% sucrose as a transformation solution further increased the transformation frequency to 6.47%. Southern blot analysis showed that the transgenic plants had low transgene copy number and simple integration pattern. Green fluorescence was observed in roots and immature embryos of transgenic plants by fluorescence microscopy. Progeny analysis showed that GFP insertions were inherited in T(1) generation. The ovary-drip method would become a favorable choice for directly generating vector- and marker-free transgenic maize expressing functional genes of agronomic interest.

A transgenic dTph1 insertional mutagenesis system for forward genetics in mycorrhizal phosphate transport of Petunia

The active endogenous dTph1 system of the Petunia hybrida mutator line W138 has been used in several forward-genetic mutant screens that were based on visible phenotypes such as flower morphology and color. In contrast, defective symbiotic phosphate (P(i)) transport in mycorrhizal roots of Petunia is a hidden molecular phenotype as the symbiosis between plant roots and fungi takes place below ground, and, while fungal colonization can be visualized histochemically, P(i) transport and the activity of P(i) transporter proteins cannot be assessed visually. Here, we report on a molecular approach in which expression of a mycorrhiza-inducible bi-functional reporter transgene and insertional mutagenesis in Petunia are combined. Bi-directionalization of a mycorrhizal P(i) transporter promoter controlling the expression of two reporter genes encoding firefly luciferase and GUS allows visualization of mycorrhiza-specific P(i) transporter expression. A population of selectable transposon insertion mutants was established by crossing the transgenic reporter line with the mutator W138, from which the P(i)transporter downregulated (ptd1) mutant was identified, which exhibits strongly reduced expression of mycorrhiza-inducible P(i) transporters in mycorrhizal roots.

Development of a standard operating procedure (SOP) for the precise quantification of transgene expression levels in rice plants

Variation in transgene expression levels can result from uncontrolled differences in experimental protocols. It is important to quantify and eliminate this unwanted variation as much as possible in order to attain precision in transgenic studies. Large-scale transgenic studies could, by their design, generate additional variation. The influence of different plant growth, sampling and analysis strategies in generating spurious variation in transgene expression level quantification in rice plant populations was assessed. The use of multiple independent plant phenotypic analyses (enzymatic assays in this study) was identified as the major source of spurious variation (doubling or tripling the variation). The quantification of transgene expression levels was also found to be significantly influenced by plant age, the choice of leaf sampled and leaf size. All of these factors reduced the precision of molecular genetic studies and generated artefactual results in transgenic studies. Identification of the sources of extraneous variation allowed the development of a new standard operating procedure (SOP) for rice, designed to control spurious variation. SOP allowed the influence of differences in growth period and independent phenotypic analyses to be minimized. The coefficient of variation in transgene expression levels, between and within genetically identical rice plants, was reduced to approximately 10 to 15% using SOP. Adoption of quality assurance (QA) criteria such as SOP is key to improving the reproducibility of transgenic studies.

Biolistic transformation of haploid isolated microspores of barley (Hordeum vulgare L.)

Transgenic barley plants were produced by the direct delivery of plasmid DNA into isolated microspores of barley cv. Igri using high velocity microprojectiles. The plasmid pAHC25 contained the uidA and bar genes, each under the control of a maize Ubi1 promoter. Bombarded microspores were cultured and selected on solid medium containing varying concentrations (2–5 mg/L) of the Basta herbicide active agent bialaphos. The effectiveness of selection with bialaphos depended on its interaction with the medium component glutamine. Six transgenic plants (R0) were obtained, and the presence of the uidA and bar genes and their integration into nuclear DNA in transformed R0 plants were confirmed by PCR and Southern blot analysis. Phosphinothricin acetyltransferase activity was observed in all six R0 transgenic plants, whereas none showed β-glucuronidase (GUS) activity in histochemical GUS assays. Two of the six R0 plants were haploid and sterile; one of them was trisomic and partially sterile; the remainder were diploid, but one of them was also sterile. Inheritance of the transgenes in progeny of three seed-producing transgenic plants was investigated. Southern blot analysis of genomic DNA from R1 plants showed that the introduced bar and uidA genes were hemizygous and stably cotransmitted to the R1 progeny derived from self-pollination. Analysis of Basta resistance and the integration of the bar gene by PCR analysis in R1 plants indicated that the bar gene was being inherited and expressed as a single dominant trait. Fluorescent in situ hybridization was performed on chromosomes of the trisomic plant to confirm the presence of transgenes in the genome.Key words: barley, microspore, biolistic transformation, bialaphos, haploid, FISH.

Expression and inheritance of foreign genes in transgenic peanut plants generated byAgrobacterium-mediated transformation

To evaluate and characterize the stability of traits transferred viaAgrobacterium transformation, foreign gene expression must be examined in sexually derived progeny. The objective of this study was to analyze three transgenic peanut plants, 1-10, 12-1, and 17-1, for the inheritance and expression of their foreign genes. Segregation ratios for the introduced genes in T₂ plants gave either 100% or 3:1 expression of the β-glucuronidase (GUS) gene, demonstrating recovery of both homozygous and heterozygous T₁ plants. Fluorometric GUS assay in T₁ and T₂ generations of all three plants showed that the GUS gene was stably expressed in the progeny. DNA analyses showed 100% concordance between the presence of the foreign gene and enzyme activity. Our results demonstrate that transgenes in peanut introduced byAgrobacterium can be inherited in a Mendelian manner.