In planta strategies for the development of transgenic plants
Authors: Rohini Sreevathsa ^*, Basavaprabhu L. Patil, and Monika Dalal
National Research Centre on Plant Biotechnology, Pusa, New Delhi-110012
^*Corresponding Author E-mail: rohinisreevathsa@rediffmail.com

Plant biotechnology has gained considerable importance and is vital for various crop improvement programmes. It has great prospective to enhance crop productivity through increasing resistance to diseases, pests and environmental stresses. Crop improvement through transgenic technology is one of the most impending and viable option in the recent times. Further, the powerful combination of genetic engineering and conventional breeding programmes permits introduction of useful traits into economically important crop species. Two important pre-requisites to develop transgenic plants is the susceptibility to Agrobacterium and the ability to regenerate. Not all plants are amenable to regeneration. Such plants are called as 'difficult to regenerate' or 'recalcitrant species'. Many economically important crop species like cotton, pigeon pea, cassava, groundnut etc fall under this group. To overcome the lag that these species face for crop improvement, alternate approaches have been developed for genetic transformation. These are called as the In Planta transformation protocols. The strategy was initially conceptualized in Arabidopsis when scientists demonstrated that transgenics with stably integrated transgenes could be developed by following Agrobacterium-mediated transformation by vacuum infiltration of flowers and floral dip (Feldmann and Marks, 1987; Betchold et al., 1993). Since then various In Planta transformation strategies have been developed and validated for stable integration. These strategies can be potential alternatives for the cumbersome regeneration-based strategies that are generally followed. Different explants have also been used for transformation like, seeds, apical meristem, fruits etc (Manoj Kumar et al., 2014).

One of the promising targets for In Planta transformation has been the shoot apical meristem. There have been several reports demonstrating the successful transfer and inheritance of transgenes using this strategy (Rohini and Rao, 2000; 2001; Manjulatha et al., 2014). The apical meristem-targeted strategy involves In Planta inoculation of embryo axes of germinating seeds with Agrobacterium and allowing them to grow into seedlings ex vitro. Since differentiating cells are targeted, the plants developed in the T0 generation are chimeric, and stable transformants are obtained in the T1 generation. Crop-specific protocols for transformation with suitable selectable markers for efficient screening of T1 plants to identify stable transformants have been developed following this strategy. In several crop species (cotton, pigeon pea, groundnut) besides reporter genes, transgenics with improved agronomic traits were also developed. However, the major crux for the success of the strategy lies in the stringent screening of the T1 generation plants for the identification of the putative transformants. Various selectable marker genes coding for herbicide resistance, antibiotic resistance can be used for this purpose. These stringent screening methods not only select the transformants but can also help in the identification of high expressing transformants based on the selection pressure.

Therefore, uniqueness of the In Planta transformation technology is, (a) it is genotype independent, (b) able to generate transgenics in recalcitrant local crops, (c) has the ability to generate large number of transgenic events.

These methods can be effectively used in any of the crop species, provided it is susceptible to Agrobacterium infection. Incorporation of such methods of gene transfer will accelerate crop improvement.

References

1. Feldmann K. A and Marks M. D (1987) Agrobacterium-mediated transformation of germinating seeds of Arabidopsis thaliana: a non-tissue culture approach. Mol. Gen. Genet. 208: 1-9

2. Betchold N., Ellis J and Pelletier G (1993) In Planta Agrobacterium-mediated gene transfer by infiltration of adult Arabidopsis thaliana plants. CR Acad Sci Paris Life Sci. 316: 1194-1199.

3. Manoj-Kumar Arthikala, Kalpana Nanjareddy, Miguel Lara, Rohini Sreevathsa (2014). Utility of a tissue culture-independent Agrobacterium-mediated In Planta transformation strategy in bell pepper to develop fungal disease resistant plants. Sci horticulturae 170: 61-69.

4. Rohini V. K. and Rao K. S (2000). Transformation of peanut (Arachis hypogaea L.): A non-tissue culture based approach for generating transgenic plants. Plant Sci., 150(1): 41-49.

5. Rohini V. K. and Rao K. S (2001). Transformation of peanut (Arachis hypogaea L.) with tobacco chitinase gene: variable response of transformants to leaf spot disease. Plant Sci., 160 (5): 883-892.

6. M. Manjulatha, Rohini Sreevathsa, A. Manoj Kumar, Chinta Sudhakar, T. G. Prasad, Narendra Tuteja and M. Udayakumar. (2014) Overexpression of a Pea DNA Helicase (PDH45) in Peanut (Arachis hypogaea L.) Confers Improvement of Cellular Level Tolerance and Productivity Under Drought Stress. Molecular Biotechnology. 56:111-125.

About Author / Additional Info:
I am a Senior Scientist at National Research Centre on Plant biotechnology, IARI campus, Pusa. My major research interest is in the field of development of transgenics for biotic stress tolerance