Abstract
Setaria viridis has many attributes, including small stature and simple growth requirements, that make it attractive as a model species for monocots. Genetic engineering (transformation) methodology is a key prerequisite for adoption of plant species as models. Various transformation approaches have been reported for S. viridis including tissue culture-based and in planta by Agrobacterium tumefaciens infection of floral organs referred to as the floral dip method. The tissue culture-based method utilizes A. tumefaciens infection of mature seed-derived callus with subsequent recovery of stable transgenic lines. Vectors found to be most effective contain the hygromycin phosphotransferase selectable marker gene driven by either Panicum virgatum or Zea mays ubiquitin promoters. As for the floral dip method, there are two reports based on Agrobacterium infection of young S. viridis inflorescences. Plants were allowed to mature, seeds were collected, and analysis of the progeny verified the presence of transgenes. Each transformation approach, tissue culture-based and floral dip, has advantages and disadvantages depending on the expertise of personnel and resources available. While the tissue culture-based method results in a higher transformation efficiency than floral dip, implementation requires a specific technical skillset that limits availability of experienced personnel to successfully perform transformations. Less technical experience is required for floral dip; however, a lack of high-quality growth chambers or greenhouses that provide the necessary optimum growing conditions would reduce an already low transformation efficiency or would not result in recovery of transgenic lines. An overview of transformation methods reported for S. viridis is presented in this review.
Highlights
Setaria viridis is the weedy, wild ancestor of the domesticated Setaria italica, which is an important food crop in some eastern Asian countries (Dekker, 2003)
Being that S. viridis is a C4 photosynthesis grass, further interest in S. viridis as a model monocot species was driven by the potential of its usefulness in advancing knowledge of the cellular and biochemical mechanisms of C4 photosynthesis (Brutnell et al, 2015)
The purpose of this review is to provide an overview of information presented at the Second International Setaria Genetics Conference on the status of genetic engineering approaches developed for S. viridis (Zhu et al, 2017)
Summary
Setaria viridis is the weedy, wild ancestor of the domesticated Setaria italica (foxtail millet), which is an important food crop in some eastern Asian countries (Dekker, 2003). The first report of transformation was based on Agrobacterium infection of mature-seed derived callus of S. viridis A10.1 (Brutnell et al, 2010) Modifications of this method and strategies to improve the efficiency including decreasing the time for recovery of transgenic lines have been made. Wang et al (1998) demonstrated that an intron-containing version of hpt resulted in higher transformation efficiencies for rice than a non-intron-containing version This result combined with those reported by Van Eck et al (2017) points to the importance of vector selection, namely, the composition of the selectable marker gene cassette, for S. viridis transformation. In the years since the first report by Brutnell et al (2010) on S. viridis’ potential as a model that included preliminary information on Agrobacterium-mediated transformation of mature seed-derived callus, some key factors related to callus generation and plant regeneration were identified that improved
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