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Abstract The production of embryogenic callus and somatic embryos is integral to the genetic improvement of crops via genetic transformation and gene editing. Regenerable embryogenic cultures also form the backbone of many micro‐propagation processes for crop species. In many species, including maize, the ability to produce embryogenic cultures is highly genotype dependent. While some modern transformation and genome editing methods reduce genotype dependence, these efforts ultimately fall short of producing truly genotype‐independent tissue culture methods. Recalcitrant genotypes are still identified in these genotype‐flexible processes, and their presence is magnified by the stark contrast with more amenable lines, which may respond more efficiently by orders of magnitude. This review aims to describe the history of research into somatic embryogenesis, embryogenic tissue cultures, and plant transformation, with particular attention paid to maize. Contemporary research into genotype‐flexible morphogenic gene‐based transformation and genome engineering is also covered in this review. The rapid evolution of plant biotechnology from nascent technologies in the latter half of the 20th century to well‐established, work‐horse production processes has, and will continue to, fundamentally changed agriculture and plant genetics research.
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A key to totipotency: Wuschel‐like homeobox 2a unlocks embryogenic culture response in maize ( Zea mays L.)
Summary The ability of plant somatic cells to dedifferentiate, form somatic embryos and regenerate whole plantsin vitrohas been harnessed for both clonal propagation and as a key component of plant genetic engineering systems. Embryogenic culture response is significantly limited, however, by plant genotype in most species. This impedes advancements in both plant transformation‐based functional genomics research and crop improvement efforts. We utilized natural variation among maize inbred lines to genetically map somatic embryo generation potential in tissue culture and identify candidate genes underlying totipotency. Using a series of maize lines derived from crosses involving the culturable parent A188 and the non‐responsive parent B73, we identified a region on chromosome 3 associated with embryogenic culture response and focused on three candidate genes within the region based on genetic position and expression pattern. Two candidate genes showed no effect when ectopically expressed in B73, but the geneWox2awas found to induce somatic embryogenesis and embryogenic callus proliferation. Transgenic B73 cells with strong constitutive expression of the B73 and A188 coding sequences ofWox2awere found to produce somatic embryos at similar frequencies, demonstrating that sufficient expression of either allele could rescue the embryogenic culture phenotype. Transgenic B73 plants were regenerated from the somatic embryos without chemical selection and no pleiotropic effects were observed in theWox2aoverexpression lines in the regenerated T0 plants or in the two independent events which produced T1 progeny. In addition to linking natural variation in tissue culture response toWox2a, our data support the utility ofWox2ain enabling transformation of recalcitrant genotypes.
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- Award ID(s):
- 1917138
- PAR ID:
- 10425867
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Plant Biotechnology Journal
- Volume:
- 21
- Issue:
- 9
- ISSN:
- 1467-7644
- Page Range / eLocation ID:
- p. 1860-1872
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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