By Alyssa Kearly
Looking around, you might not realize it, but corn is everywhere. In one form or another, it's in the cereals in your cupboard, the cosmetics and medicines in your bathroom, the kibble in your pet's food bowl, and the gas tank of your car.
Corn, or maize, is a major crop in the United States, and its derivatives are utilized in practically every facet of our lives. Demand for it grows, even as unpredictable environmental conditions make it difficult for farmers to maintain their current yield.
For millennia, humans have intentionally bred crops to fit the ever-evolving needs of society. Nowadays, with advancements in science and technology, we can bioengineer crops by tweaking their genomes—the plants' biological blueprints—to create drought-resistant, higher-yield, and extra-nutritious versions to fulfill our modern needs.
However, for some crop species, including maize, bioengineering is technically challenging and requires resources unavailable at many research institutions. In work recently published in the journal In Vitro Cellular & Developmental Biology—Plant, labs from the Boyce Thompson Institute (BTI) and Iowa State University (ISU) partnered with scientists from Corteva Agriscience to establish a more accessible method for maize bioengineering that will pave the way for improving this critical crop.
Traditional bioengineering methods for maize use very small, immature embryos harvested from the corn kernels of mature plants. These embryos undergo a procedure called transformation, in which a specially designed piece of DNA is transferred to the maize genome to imbue the plants with a desired trait. For instance, a maize plant can be given a gene that boosts its resistance to a disease that could otherwise decimate a farmer's field.
The success rate for this method of transformation depends heavily on the quality of the embryos, and high-quality embryos require advanced growing facilities. But as Dr. Joyce Van Eck, professor at BTI and one of the lead researchers on the project, divulged, "Few academic research groups have the infrastructure necessary for growing the high-quality maize required for transformation, so the method has largely been restricted to commercial industry."
Success also depends on the type of maize, or genotype, being transformed, as each genotype has a distinct genetic makeup and variations in traits. "Many labs use the B73 genotype as a standard for experiments," explained Dr. Ritesh Kumar, a postdoctoral researcher in the Van Eck lab and first author on the study, "but it's very difficult to transform B73 embryos." Thus, it has been onerous to use this maize genotype to study gene function.
These factors have all contributed to what Dr. Van Eck described as a "bottleneck" in maize research: scientists are limited in what they can accomplish by resource-intensive, non-ideal transformation techniques.
To make maize transformation more accessible, the researchers adapted a technique recently developed by Corteva Agriscience scientists, in which the compact bundle of developing leaves, or leaf whorls, of young seedlings are used for transformation in lieu of embryos from mature plants. Using this method, plants only need to grow for about two weeks and do not need to reach maturity for embryo harvesting, reducing both the time involved and the need for advanced growing facilities.
This leaf whorl transformation method originally utilized a proprietary helper plasmid developed at Corteva Agriscience, which provided the molecular tools necessary for transferring the specially designed piece of DNA to the maize genome. In the current study, the researchers tested the performance of an alternative, publicly available helper plasmid developed by a group led by Dr. Kan Wang, professor in the Department of Agronomy at ISU.
Overall, the study tested the efficacy of the leaf whorl transformation method with the two different helper plasmids in two maize genotypes—PHR03 and the notoriously recalcitrant genotype B73. With the publicly available helper plasmid, the researchers reported similarly high success rates in both genotypes, demonstrating that this more accessible transformation method is effective even in resistant maize.
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