Fluorescent reporters for functional analysis in rice leaves

A single promoter-TALE system for tissue-specific and tuneable expression of multiple genes in rice

In biological discovery and engineering research, there is a need to spatially and/or temporally regulate transgene expression. However, the limited availability of promoter sequences that are uniquely active in specific tissue-types and/or at specific times often precludes co-expression of multiple transgenes in precisely controlled developmental contexts. Here, we developed a system for use in rice that comprises synthetic designer transcription activator-like effectors (dTALEs) and cognate synthetic TALE-activated promoters (STAPs). The system allows multiple transgenes to be expressed from different STAPs, with the spatial and temporal context determined by a single promoter that drives expression of the dTALE. We show that two different systems-dTALE1-STAP1 and dTALE2-STAP2-can activate STAP-driven reporter gene expression in stable transgenic rice lines, with transgene transcript levels dependent on both dTALE and STAP sequence identities. The relative strength of individual STAP sequences is consistent between dTALE1 and dTALE2 systems but differs between cell-types, requiring empirical evaluation in each case. dTALE expression leads to off-target activation of endogenous genes but the number of genes affected is substantially less than the number impacted by the somaclonal variation that occurs during the regeneration of transformed plants. With the potential to design fully orthogonal dTALEs for any genome of interest, the dTALE-STAP system thus provides a powerful approach to fine-tune the expression of multiple transgenes, and to simultaneously introduce different synthetic circuits into distinct developmental contexts.

Genetic transformation of common beans (Phaseolus vulgaris L.) through Agrobacterium tumefaciens carrying Cry1Ab gene

BACKGROUND

Seed beetles are one of the most important causes of yield loss in bean production. It is essential to develop resistant varieties in the fight against these pests. Agrobacterium-based gene transformation is the most widely used breeding method worldwide to develop insect-resistant varieties.

METHODS AND RESULTS

Embryonic axes and plumule explants were obtained from Agrobacterium tumefciens treated mature zygotic embryos of low and high raw protein-based common bean cultivars Akman 98 and Karacaşehir 90. Agrobacterium tumefaciens contained a synthetic Bacillus thuringiensis insecticidal crystal protein gene (Bt Cry1Ab) controlled by the 35S promoter and NOS terminator sequences. The transformation event was genotype and explant dependent. The plumule explants could not withstand kanamycin-based selection pressure and died. It was possible to get two transgenic plants using embryonic axis explants of low protein cultivar Akman 98. These results were validated using GUS analysis, PCR, RT-PCR, bioassay analysis, and ELISA test from the samples taken from T₀ and T₁ generations. Bioassay tests showed that these plants were protected from the damage of legume seed insects (Bruchus spp.).

CONCLUSIONS

The results are very encouraging and may help in producing better transgenic common bean germplasm leading to safe agriculture and reducing environmental pollutions.

Flip-Flap: A Simple Dual-View Imaging Method for 3D Reconstruction of Thick Plant Samples

Plant development is a complex process that relies on molecular and cellular events being co-ordinated in space and time. Microscopy is one of the most powerful tools available to investigate this spatiotemporal complexity. One step towards a better understanding of complexity in plants would be the acquisition of 3D images of entire organs. However, 3D imaging of intact plant samples is not always simple and often requires expensive and/or non-trivial approaches. In particular, the inner tissues of thick samples are challenging to image. Here, we present the Flip-Flap method, a simple imaging protocol to produce 3D images of cleared plant samples at the organ scale. This method allows full 3D reconstruction of plant organs suitable for 3D segmentation and further related analysis and can be easily handled by relatively inexperienced microscopists.

Optimizing the Protein Fluorescence Reporting System for Somatic Embryogenesis Regeneration Screening and Visual Labeling of Functional Genes in Cotton

Protein fluorescence reporting systems are of crucial importance to in-depth life science research, providing systematic labeling tools for visualization of microscopic biological activities in vivo and revolutionizing basic research. Cotton somatic cell regeneration efficiency is low, causing difficulty in cotton transformation. It is conducive to screening transgenic somatic embryo using the fluorescence reporting system. However, available fluorescence labeling systems in cotton are currently limited. To optimize the fluorescence reporting system of cotton with an expanded range of available fluorescent proteins, we selected 11 fluorescent proteins covering red, green, yellow, and cyan fluorescence colors and expressed them in cotton. Besides mRuby2 and G3GFP, the other nine fluorescent proteins (mCherry, tdTomato, sfGFP, Clover, EYFP, YPet, mVenus, mCerulean, and ECFP) were stably and intensely expressed in transgenic callus and embryo, and inherited in different cotton organs derive from the screened embryo. In addition, transgenic cotton expressing tdTomato appears pink under white light, not only for callus and embryo tissues but also various organs of mature plants, providing a visual marker in the cotton genetic transformation process, accelerating the evaluation of transgenic events. Further, we constructed transgenic cotton expressing mCherry-labeled organelle markers in vivo that cover seven specific subcellular compartments: plasma membrane, endoplasmic reticulum, tonoplast, mitochondrion, plastid, Golgi apparatus, and peroxisome. We also provide a simple and highly efficient strategy to quickly determine the subcellular localization of uncharacterized proteins in cotton cells using organelle markers. Lastly, we built the first cotton stomatal fluorescence reporting system using stomata-specific expression promoters (ProKST1, ProGbSLSP, and ProGC1) to drive Clover expression. The optimized fluorescence labeling system for transgenic somatic embryo screening and functional gene labeling in this study offers the potential to accelerating somatic cell regeneration efficiency and the in vivo monitoring of diverse cellular processes in cotton.

A Rapid and Highly Efficient Method for Transient Gene Expression in Rice Plants

Rice is the model plant system for monocots and the sequencing of its genome has led to the identification of a vast array of genes for characterization. The tedious and time-consuming effort of raising rice transgenics has significantly delayed the pace of rice research. The lack of highly efficient transient assay protocol for rice has only added to the woes which could have otherwise helped in rapid deciphering of the functions of genes. Here, we describe a technique for efficient transient gene expression in rice seedlings. It makes use of co-cultivation of 6-day-old rice seedlings with Agrobacterium in the presence of a medium containing Silwet^® L-77, acetosyringone and glucose. Seedlings can be visualized 9 days after co-cultivation for transient expression. The use of young seedlings helps in significantly reducing the duration of the experiment and facilitates the visualization of rice cells under the microscope as young leaves are thinner than mature rice leaves. Further, growth of seedlings at low temperature, and the use of surfactant along with wounding and vacuum infiltration steps significantly increases the efficiency of this protocol and helps in bypassing the natural barriers in rice leaves, which hinders Agrobacterium-based transformation in this plant. This technique, therefore, provides a shorter, efficient and cost-effective way to study transient gene function in intact rice seedling without the need for a specialized device like particle gun.

A series of dual-reporter vectors for ratiometric analysis of protein abundance in plants

Ratiometric reporter systems enable comparisons of the abundance of a protein of interest, or "target," relative to a reference protein. Both proteins are encoded on a single transcript but are separated during translation. This arrangement bypasses the potential for discordant expression that can arise when the target and reference proteins are encoded by separate genes. We generated a set of 18 Gateway-compatible vectors termed pRATIO that combine a variety of promoters, fluorescent, and bioluminescent reporters, and 2A "self-cleaving" peptides. These constructs are easily modified to produce additional combinations or introduce new reporter proteins. We found that mScarlet-I provides the best signal-to-noise ratio among several fluorescent reporter proteins during transient expression experiments in Nicotiana benthamiana. Firefly and Gaussia luciferase also produce high signal-to-noise in N. benthamiana. As proof of concept, we used this system to investigate whether degradation of the receptor KAI2 after karrikin treatment is influenced by its subcellular localization. KAI2 is normally found in the cytoplasm and the nucleus of plant cells. In N. benthamiana, karrikin-induced degradation of KAI2 was only observed when it was retained in the nucleus. These vectors are tools to easily monitor in vivo the abundance of a protein that is transiently expressed in plants, and will be particularly useful for investigating protein turnover in response to different stimuli.