Abstract
Maize is an important food and feed crop in many countries. It is also one of the most important target crops for the application of biotechnology. Currently, there are more biotech traits available on the market in maize than in any other crop. Generation of transgenic events is a crucial step in the development of biotech traits. For commercial applications, a high throughput transformation system producing a large number of high quality events in an elite genetic background is highly desirable. There has been tremendous progress in Agrobacterium-mediated maize transformation since the publication of the Ishida et al. (1996) paper and the technology has been widely adopted for transgenic event production by many labs around the world. We will review general efforts in establishing efficient maize transformation technologies useful for transgenic event production in trait research and development. The review will also discuss transformation systems used for generating commercial maize trait events currently on the market. As the number of traits is increasing steadily and two or more modes of action are used to control key pests, new tools are needed to efficiently transform vectors containing multiple trait genes. We will review general guidelines for assembling binary vectors for commercial transformation. Approaches to increase transformation efficiency and gene expression of large gene stack vectors will be discussed. Finally, recent studies of targeted genome modification and transgene insertion using different site-directed nuclease technologies will be reviewed.
Highlights
Maize is an important food and feed crop around the world
Since assembly of TALEN and CRISPR-Cas9 nucleases can be carried out using standard molecular biology techniques, it is conceivable that their application in basic research for understanding the maize genome and in commercial trait development will progress rapidly in the coming years
This review will cover some of the aspects of maize transformation that are important from a commercial trait development point of view
Summary
Maize is an important food and feed crop around the world. Since the market launch of the first transgenic Bt maize products in the mid-1990s, maize has become one of the most important target crops for biotechnological innovation. To address the fertility issue of earlier studies Shillito et al (1989) reported the use of Type II embryogenic calli derived from cultured immature embryos of an elite inbred line to generate embryogenic suspension cell cultures that can stay highly regenerable for several months These cultures can be harvested to isolate protoplasts for transformation. Not long after the first reports of successful maize transformation using protoplasts were published, microparticle bombardment ( known as biolistic transformation) was successfully demonstrated to generate highly fertile maize transformants using embryogenic suspension cell cultures or calli as target tissue and the BAR (bialaphos resistance), ALS (acetolactate synthase), or HPT (hygromycin phosphotransferase) genes as selectable markers (Fromm et al, 1990; Gordon-Kamm et al, 1990; Walters et al, 1992; Vain et al, 1993).
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