An Efficient and Highly Reproducible Approach for the Selection of Upland Transgenic Cotton Produced by Pollen Tube Pathway Method
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AJCS 7(11):1714-1722 (2013) ISSN:1835-2707 An efficient and highly reproducible approach for the selection of upland transgenic cotton produced by pollen tube pathway method Noreen Bibi1,2, Kai Fan1, Shuna Yuan1, Mi Ni1, Imrul Mosaddek Ahmed1, Waqas Malik1, 3, Xuede Wang1* 1Department of Crop Sciences, College of Agriculture and Biotechnology, Zijingang Campus, Zhejiang University, Yu Hang Tang Road 866, Hangzhou 310058, PR China 2Plant Breeding Genetics Division, Nuclear Institute for Agriculture and Biology (NIAB), Jhang Road Faisalabad, Pakistan 3Department of Plant Breeding and Genetics, Bahauddin Zakariya University, Multan, Pakistan Corresponding author: [email protected] Abstract Pollen tube pathway mediated transformation is most favorable genotype-independent approach and has been widely used for the production of transgenic crops all over the world. We used this technique to transform Zheda B, an upland cotton, by two different vectors i.e. pCAMBIA1301 with hpt gene for hygromycin resistance and pCAMBIA 2301 having nptII gene for kanamycin resistance. A preliminary experiment was conducted to find out suitable concentration of kanamycin (100-600 mg/L) and hygromycin (25-150 mg/L) for the screening of transgenic plants. Results revealed that both antibiotics caused a significant reduction in seed germination, seedling survival, plant height, root length, fresh and dry weight of root and shoot as compared to their respective controls. Furthermore, 500 mg/L kanamycin and 75 mg/L hygromycin were established as effective dozes to eliminate 80- 85% of non-transgenic seedlings during seedling stage. The outcomes of the preliminary experiment were applied to select transgenic plants from T1 population, which were later confirmed by PCR and GUS staining. The results were identification of positive transgenic plants with successful integration of GUS gene into recipient cotton genome. Comparing both antibiotics, upland cotton was found to be more sensitive to hygromycin application as compared to kanamycin. Therefore, designing gene constructs for pollen tube pathway mediated transformation; hptII gene seems to be more appropriate choice than nptII gene for selection of transgenic plants. The protocols are robust and can be utilized for other crop species as well. Keywords: Cotton transformation, leaf painting, growth inhibition, pollen tube pathway, seed germination, seedling survival. Abbreviations: DPA_days post anthesis, GUS_β-glucuronidase, hpt_hygromycin phosphotransferase, nptII_neomycin phosphotransferase II, pNOS_nopaline synthase promoter. Introduction Production of transgenic crops with desirable traits is of During the process of transformation, some cells from paramount importance to meet the global needs of food, feed nucellus tissue degenerate to make a channel for the entry of and fiber; and has much more advantages as compared to pollen tube towards embryo sac. This pathway is usually traditional breeding techniques. Transgenic plant larger than pollen tube, so heterologous DNA can easily enter development is mainly based upon Agrobacterium into embryo sac and gets incorporated into recipient plant tumifaciens mediated transformation that accounts for genome (Song et al., 2007). The approach though did not production of 80% transgenic crops around the world (Wang require highly exclusive conditions for transformation of and Fang, 1998). This method of genetic transformation is exogenous DNA but results in the production of thousands of exclusively genotype dependent and needs extremely seeds after transformation. Due to less availability of land, sterilized conditions during transformation and tissue sometimes it becomes unattainable to directly sow all the regeneration. Due to this reason, this technique has been seeds in the field and to follow commonly adopted methods restricted to well develop laboratories only. In contrast, of transgenic screening like leaf painting, PCR and southern pollen tube pathway is a genotype-independent approach and blotting. Therefore, it is necessary to develop some cost provided first-hand choice for crop varieties lacking effective and reproducible methods to eliminate most of non- regeneration potential. This technique has been widely transgenic plants at seedling stage. During gene practiced for developing transgenic cotton (Zhou et al., transformation, a common phenomenon associated with 1983), rice (Luo and Wu, 1988) and soybean (Lei et al., exogenous genes is that they do not bestow a phenotype that 1991; Liu et al., 1992) and can easily produce next generation can be used conveniently for the identification of transgenic seeds (Song et al., 2007). The technique is very simple and cells. For this reason, phenotypically identifiable marker follows injection of foreign DNA to stigma after one day of genes are co-transformed along with the gene of interest to post anthesis (DPA) (Zhou et al., 1983). selectively eliminate non-transformed tissues. 1714 A selectable marker gene usually encodes a product that to that of 200 mg/L (Fig. 1), but subsequent higher doses allows the transformed cell to survive and grow under resulted gradual reduction in seedling survival with conditions that can either kill or restrict the growth of non- maximum reduction of 78% attained at highest concentration transformed cells. Most commonly used marker genes are level (600 mg/L). On the other hand, the reduction in nptII (kanamycin resistant), hpt (hygromycin resistant) Bar seedling survival was highly significant up to 75 mg/L of (herbicide tolerant) and pat encoding phosphinothricin acetyl hygromycin relative to control, but none of the seedlings transferase; and have been extensively used for the selection could survive at concentration higher than 75 mg/L (Fig. 3b, of transgenic plants (Leelavathi, 2004; Zhang and 4). Moreover, at C3 level, the seedling survival for Shangguan, 2006; Visarada et al. 2008; Daud et al., 2009; kanamycin was 55% while for hygromycin it was only 15% Zhang et al., 2010; Afolabi Balogun et al., 2011). Kanamycin as compared to 90% of control. Therefore, comparing both is one kind of amino glycoside antibiotic, which inhibits the antibiotics, upland cotton was found to be more sensitive to protein synthesis in green parts of the plants (Nap et al., application of hygromycin. Concomitant with our results, 1992; Lu et al., 2001; Wang and Yi, 2003; Chen et al., 2005). shoot development in case of grapevine was also found to be The cells incorporated with nptII gene offer resistance to more sensitive to the application of hygromycin as compared kanamycin application; while non-transformed cells either to kanamycin (Torregrosa et al., 2000; Clevenger et al., 2004; get died or show restrained growth. In this regard, Walters et al., 2010). But previous researchers (Guellec et al., appropriate concentration of antibiotics is one of the most 1990; Mullins et al., 1990; Mauro et al., 1995) have critical factors for screening of transgenic plants. If the associated the failure of shoot development with the concentration of antibiotic is too low, it results in the inefficiency of nptII gene, when it is controlled by pNOS, selection of false positive plants while concentration rather than assuming grapevine to be sensitive to kanamycin. exceeding the resistance level can cause mortality of transgenic plants as well. Previous report demonstrated the Morphological parameters of upland cotton seedlings germination of cotton seeds on MS media supplemented with appropriate amount of antibiotics (Li et al., 2004). However, Plants were uprooted and various growth parameters were presence of sucrose/glucose in MS media escalates growth of studied. Results revealed significant variations (p < 0.05) in microorganisms including bacteria and fungus; and therefore seedling vigor. The plants raised from seeds initially needs extremely sterilized conditions. Present study utilized germinated on media containing antibiotics were remained water agar media as an alternative to MS media, which is dwarf while their respective controls grew normally attaining highly cost effective, and has produced similar outcomes. plant height of about 35 cm (Fig. 5 A). Plant height was Hence, the current study was planned to select terrific sharply declined up to 52 % of control at 200 mg/L of concentration of both kanamycin/hygromycin and growth kanamycin and was statistically similar up to 400 mg/L indices which can be utilized to abolish non transgenic plants followed by another sharp decrease at 500-600 mg/L. under field and lab conditions. Elimination of non-transgenic Whereas, in case of hygromycin plant height was highly dose seeds and seedling will not only reduce the work for dependent and continuously decreased with increase in molecular studies but will also facilitate the timely selection applied concentration level (Fig. 5 A). At C2 level of both of transgenic plants within a specific growing season. kanamycin (200 mg/L) and hygromycin (50 mg/L) plant height was about 18-20 cm as compared to 35 cm observed Results and discussion for control. Root is considered as the most important organ and determines the overall health of the plant. It not only Effects of antibiotics treatment on seed germination and anchors the plant in soil but also nourishes the plant through seedling survival active absorption of water and nutrients from soil (Hoad et al., 2001). The seedling could not recover the inhibitory Both antibiotics significantly decreased the germination of effects of antibiotics pretreatment even