Adrian R. Elliott

Green-fluorescent protein facilitates rapid in vivo detection of genetically transformed plant cells

Abstract Early detection of plant transformation events is necessary for the rapid establishment and optimization of plant transformation protocols. We have assessed modified versions of the green fluorescent protein (GFP) from Aequorea victoria as early reporters of plant transformation using a dissecting fluorescence microscope with appropriate filters. Gfp-expressing cells from four different plant species (sugarcane, maize, lettuce, and tobacco) were readily distinguished, following either Agrobacterium-mediated or particle bombardment-mediated transformation. The identification of gfp-expressing sugarcane cells allowed for the elimination of a high proportion of non-expressing explants and also enabled visual selection of dividing transgenic cells, an early step in the generation of transgenic organisms. The recovery of transgenic cell clusters was streamlined by the ability to visualize gfp-expressing tissues in vitro.

Promoters for pregenomic RNA of banana streak badnavirus are active for transgene expression in monocot and dicot plants

Two putative promoters from Australian banana streak badnavirus (BSV) isolates were analysed for activity in different plant species. In transient expression systems the My (2105 bp) and Cv (1322 bp) fragments were both shown to have promoter activity in a wide range of plant species including monocots (maize, barley, banana, millet, wheat, sorghum), dicots (tobacco, canola, sunflower, Nicotiana benthamiana, tipu tree), gymnosperm (Pinus radiata) and fern (Nephrolepis cordifolia). Evaluation of the My and Cv promoters in transgenic sugarcane, banana and tobacco plants demonstrated that these promoters could drive high-level expression of either the green fluorescent protein (GFP) or the β-glucuronidase (GUS) reporter gene (uidA) in vegetative plant cells. In transgenic sugarcane plants harbouring the Cv promoter, GFP expression levels were comparable or higher (up to 1.06% of total soluble leaf protein as GFP) than those of plants containing the maize ubiquitin promoter (up to 0.34% of total soluble leaf protein). GUS activities in transgenic in vitro-grown banana plants containing the My promoter were up to seven-fold stronger in leaf tissue and up to four-fold stronger in root and corm tissue than in plants harbouring the maize ubiquitin promoter. The Cv promoter showed activities that were similar to the maize ubiquitin promoter in in vitro-grown banana plants, but was significantly reduced in larger glasshouse-grown plants. In transgenic in vitro-grown tobacco plants, the My promoter reached activities close to those of the 35S promoter of cauliflower mosaic virus (CaMV), while the Cv promoter was about half as active as the CaMV 35S promoter. The BSV promoters for pregenomic RNA represent useful tools for the high-level expression of foreign genes in transgenic monocots.

Agrobacterium tumefaciens-mediated transformation of wheat using suspension cells as a model system and green fluorescent protein as a visual marker

Conditions for Agrobacterium-mediated transformation of wheat (Triticum aestivum L.) were defined using wheat suspension cells as a model system and green fluorescent protein (GFP) as a visual marker. Different strains of Agrobacterium tumefaciens were compared using established wheat cell suspension cultures, where the frequency of cell clusters showing transient activity of GFP ranged from 2 to 52%. High levels of transient GFP activity and stable transformed callus lines were obtained with plasmid pTO134 containing a gfp gene with an enhanced CaMV 35S promoter and a bar gene with a 35S promoter in combination with Agrobacterium strain AGL0. These results suggest that the important variables in Agrobacterium-mediated transformation of wheat cells include media composition, Agrobacterium strain, plasmid vector and the addition of virulence-inducing agents such as acetosyringone. The conditions deemed optimal for transformation of wheat suspension cell lines were applied to scutella isolated from immature embryos and scutella-derived calli. Transient GFP expression in these tissues ranged from 10 to 75% and, while quite variable among and within cultivars, stably transformed scutellum-derived callus was obtained. Further studies with scutellum-derived calli suggested that variables such as duration of pre-inoculation culture and co-cultivation, as well as co-cultivation temperature, were also important. Optimisation of these variables resulted in the recovery of transformed wheat plants at a transformation frequency of 1.8%, which is comparable with other reports.

Assessment of transient gene expression in plant tissues using the green fluorescent protein as a reference

Four different promoters (35S and enhanced 35S of the cauliflower mosaic virus, polyubiquitin of maize and actin1 of rice) were compared in a transient assay using maize leaves and particle bombardment. A gene encoding the jellyfish green fluorescent protein (GFP) driven by the 35S promoter was used as an internal standard to monitor the effectiveness of each bombardment. Normalisation of the transient expression assay using the GFP reference significantly reduced the variability between separate bombardments and allowed for a rapid and accurate evaluation of different promoters in microprojectile-bombarded leaves.