Abstract
Modern maize exhibits a significantly different phenotype than its wild progenitor teosinte despite many genetic similarities. Of the many subspecies of Zea mays identified as teosinte, Zea mays ssp. parviglumis is the most closely related to domesticated maize. Understanding teosinte genes and their regulations can provide great insights into the maize domestication process and facilitate breeding for future crop improvement. However, a protocol of genetic transformation, which is essential for gene functional analyses, is not available in teosinte. In this study, we report the establishment of a robust callus induction and regeneration protocol using whorl segments of seedlings germinated from mature seeds of Zea parviglumis. We also report, for the first time, the production of fertile, transgenic teosinte plants using the particle bombardment. Using herbicide resistance genes such as mutant acetolactate synthase (Als) or bialaphos resistance (bar) as selectable markers, we achieved an average transformation frequency of 4.17% (percentage of independent transgenic events in total bombarded explants that produced callus). Expression of visual marker genes of red fluorescent protein tdTomato and β-glucuronidase (gus) could be detected in bombarded callus culture and in T1 and T2 progeny plants. The protocol established in this work provides a major enabling technology for research toward the understanding of this important plant in crop domestication.
Highlights
Maize is the most important grain crop for both humans and animals
To overcome the limited production of immature embryos in teosinte plants, we used seedlings germinated from mature seeds as an alternative starting material
It is expected that the seed germination and callus initiation rates may differ between plants
Summary
Maize is the most important grain crop for both humans and animals. It is widely believed that the ancestor of modern maize (Zea mays ssp. mays) is the Mesoamerican plant teosinte. Swedlund and Locy (1988) reported the establishment of embryogenic callus using both immature embryos and immature leaf tissue of Zea diploperennis on MS/sucrose-based growth media containing 2,4-D. These callus cultures were maintained for up to 2 years after callus induction was initiated. They were able to regenerate plants from the 2-year-old callus culture on rooting media containing kinetin and examined the cellular and morphological changes They stated that “regenerated plants did not differ in chromosome numbers or general morphology from the original plants placed in culture” (Swedlund and Locy, 1988). They found that laterally cut shoots collected from the field could be propagated into clonal plants rapidly when placed onto growth medium containing 5 μM 6-benzylamino purine (BAP) to induce multishoot formation from meristematic regions (Zale et al, 2008)
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