发布: 2020年09月05日第10卷第17期 DOI: 10.21769/BioProtoc.3739 浏览次数: 11105
评审: Guotian LiDaniel F. CaddellAnonymous reviewer(s)
Abstract
Genetic transformation is crucial for both investigating gene functions and for engineering of crops to introduce new traits. Rice (Oryza sativa L.) is an important model in plant research, since it is the staple food for more than half of the world’s population. As a result, numerous transformation methods have been developed for both indica and japonica rice. Since breeders continuously develop new rice varieties, transformation protocols have to be adapted for each new variety. Here we provide an optimized transformation protocol with detailed tips and tricks for a new African variety Komboka using immature embryos. In Komboka, we obtained an apparent transformation rate of up to 48% for GUS/GFP reporter gene constructs using this optimized protocol. This protocol is also applicable for use with other elite indica rice varieties.
Keywords: Agrobacterium-mediated transformation (农杆菌介导转化)Background
Various methods for genetic transformation of plants have been developed, e.g. PEG-mediated transfection of protoplasts (Shimamoto et al., 1989; Datta et al., 1992), biolistic transformation (Christou et al., 1991) and Agrobacterium-mediated transformation (Slamet-Loedin et al., 2014). Agrobacterium-mediated transformation is one of the most widely used methods to introduce DNA into plants (van Wordragen and Dons, 1992). This method has been used intensively for research and has become a key prerequisite for biotechnology. It has gained in importance since the development of new breeding technologies such as genome editing (Char et al., 2019). For crops, such as rice, genetic transformation could also be used to develop new genetic variations for plant breeding, for example, creating new disease- or insect-resistant lines (Cheng et al., 1998; Helliwell and Yang, 2013; Oliva et al., 2019). Also for rice, Agrobacterium-mediated transformation is the most popular method to transfer T-DNA into plant genomes (Hiei and Komari, 2008). Currently, there are multiple protocols for japonica and indica rice transformation using calli induced from mature seeds or immature embryos (Hiei and Komari, 2006 and 2008; Toki et al., 2006; Nishimura et al., 2006; Sahoo et al., 2011; Sahoo and Tuteja, 2012; Slamet-Loedin et al., 2014; Sundararajan et al., 2017). It is convenient to use mature seeds for transformation because they are available throughout the year and can be stored, although this method is predominantly used for japonica varieties. Methods that involve transformation of rice immature embryos generally yield higher transformation rates compared to mature seeds (Hiei and Komari, 2008; Slamet-Loedin et al., 2014). Overall, japonica varieties such as Kitaake and Nipponbare are apparently easier to transform, compared to indica rice such as IR64 or Ciherang-Sub1 (Oliva et al., 2019). For japonica varieties, highly efficient transformation can be obtained using calli induced from mature seeds with rates of 50-60% (Li et al., 2015). For indica varieties, despite some efforts to increase transformation rate using mature seeds, immature embryos-derived calli are still the tissue of choice for transformation. Notably, transformation efficiency is highly variety-dependent and it is necessary to optimize transformation protocols for each variety.
Komboka (IR 05N 221) is a new elite variety generated by IRRI and released in Tanzania by the National Rice Research Program-KATRIN Research Centre and IRRI-Tanzania (‘Komboka’ = ‘liberated’) (Kitilu et al., 2019). Komboka is high yielding (8.6 t ha-1), semi-aromatic with good grain quality, tolerant to blast and well adapted to upland and lowland areas. In the protocol reported here, we describe detailed steps for the stable transformation of Komboka immature embryos which produce transgenic plants within four months and with a high apparent transformation rate of up to 48%. This protocol was developed by combining and modifying published protocols from Slamet-Loedin et al., 2014 and Hiei and Komari, 2008 which were used to transform different indica rice varieties such as IR64, Ciherang-sub1 (Oliva et al., 2019), therefore, in principle this protocol can likely be adapted for transformation of other indica rice varieties. In this protocol, we highlighted all details, tips and tricks that are essential for setting up transformation protocols for other elite varieties.
Figure 1. Flow chart and timeline for Agrobacterium-mediated transformation of immature embryos of rice var. Komboka (indica) which takes about four months to generate transgenic lines. Briefly, the process starts with growing rice plants to the flowering stage under controlled greenhouse conditions at 30 °C ± 2 °C during the day and 25 °C ± 2 °C during the night, 50-70% relative humidity. Light conditions in the glass greenhouse are determined by natural daylight and additional lamplight (8/16 day/night photoperiod). Daylength varies in the course of the seasons due to the location of our greenhouse along latitude (latitudes and longitudes of Düsseldorf, Germany 51°11'31.2"N 6°47'40.1"E). Under these conditions, Komboka required 13-14 weeks till booting stage and additional 2-3 weeks to flower. 8-12 days post-pollination, rice panicles can be harvested for immature embryos isolation. Selecting the proper stage of seeds for immature embryos isolation is crucial. Immature embryos should be in the late milky stage (Video 1), with a size of 1.3-1.8 mm. After dehusking the seeds and isolating immature embryos (Videos 2 and 3; Figure 2), the isolated immature embryos were moved, as a whole, onto co-cultivation medium. Right after the isolation step immature embryos were co-cultivated with Agrobacteria harboring constructs-of-interest for seven days. Afterwards, germinated immature embryos were cleaned from Agrobacteria with sterile filter papers and shoots were excised. The immature embryos were then transferred onto resting/recovery medium without hygromycin B for five days. After resting, immature embryos were moved to two rounds of selection with 30 mg/L hygromycin B, each for 10 days. After the second selection step, microcalli appeared on brownish maternal immature embryos. Microcalli were carefully separated from the maternal tissues and transferred onto selection medium (30 mg/L hygromycin B) for the third selection round. In cases that the immature embryos did not produce microcalli after the first two rounds of selection, immature embryos were moved to an additional selection round (Supplementary Selection 2) of 10 days each. Resistant and multiplied microcalli after the third selection were transferred onto pre-regeneration medium (30 mg/L hygromycin B) for 1 or 2 rounds of growth for 10 days. Only greening calli were transferred onto regeneration medium (30 mg/L hygromycin B) for 14 days. When small rice plants (plantlets) were regenerated from the calli and reached about 5 cm in height, they were transferred onto rooting medium without hygromycin B for 14 days. Only well-developed plantlets with strong root systems were planted in pots. Pots were submerged in larger buckets (5 L).
Figure 1. Flow chart describing Agrobacterium-mediated transformation using immature embryos of rice variety Komboka
Figure 2. Steps in Agrobacterium-mediated transformation of immature embryos from rice variety Komboka. A. Immature embryo isolation. B. Agrobacterium infection. C. Co-cultivation. D. Resting phase. E. Selection phase. F. Pre-regeneration phase. G. Regeneration phase. H. Rooting phase.
Below, we provide detailed lists of chemicals, equipment, the transformation steps with important notes, as well as all templates for media preparation.
Materials and Reagents
Consumables
Chemicals
Note: Chemical batches and brands are important factors that may affect transformation success. We found that the indistinctive use of alternative chemical brands often leads to failure when trying to transform Komboka for the first time. Therefore, we highly recommend to use the exact chemicals specified here (brands and catalog numbers), in particular when setting up a new transformation protocol. Make sure to store the chemicals in the required conditions and do not use products after the expiry dates. We declare no competing interest regarding chemicals or instrument choice.
Equipment
Note: Equipment can be adapted to different lab conditions, however, PETRI DISHES, MAGENTA BOXES are VERY IMPORTANT TOOLS which affect transformation efficiency. We highly recommend to use the same brands as we used in this protocol. SCALPELS and TWEEZERS have to be high quality due to the frequent sterilization. Exact type and brand may be adapted to personal choice.
Procedure
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文章信息
版权信息
© 2020 The Authors; exclusive licensee Bio-protocol LLC.
如何引用
Luu, V. T., Stiebner, M., Maldonado, P. E., Valdés, S., Marín, D., Delgado, G., Laluz, V., Wu, L., Chavarriaga, P., Tohme, J., Slamet-Loedin, I. H. and Frommer, W. B. (2020). Efficient Agrobacterium-mediated Transformation of the Elite–Indica Rice Variety Komboka. Bio-protocol 10(17): e3739. DOI: 10.21769/BioProtoc.3739.
分类
植物科学 > 植物转化 > 农杆菌介导的转化方法
微生物学 > 微生物遗传学 > 转化
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