Transgenic expression of a maize geranyl geranyl transferase gene sequence in maize callus increases resistance to ear rot pathogens

Authors: Dowd, Patrick; Zilkowski, Bruce; Johnson, Eric; Berhow, Mark; Muturi, Ephantus

Submitted to: AGRI GENE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2018
Publication Date: 1/3/2018
Citation: Dowd, P.F., Zilkowski, B.W., Johnson, E.T., Berhow, M.A., Muturi, E.J. 2018. Transgenic expression of a maize geranyl geranyl transferase gene sequence in maize callus increases resistance to ear rot pathogens. AGRI GENE. 7:52-58. https://doi.org/10.1016/j.aggene.2018.01.001.
DOI: https://doi.org/10.1016/j.aggene.2018.01.001

Interpretive Summary: Insects and disease greatly reduce corn yields. Corn ear molds can produce toxins harmful to people and animals, causing hundreds of millions of dollars in losses in the U.S. alone. Plant resistance is an economical means to reduce corn ear damage caused by insects and ear rots, but there continues to be a need to determine what genes are involved in producing resistance. A gene isolated from a chromosome region that was previously associated with ear rot resistance was evaluated for its resistance role. The gene produces a protein that can lead to enhanced membrane binding of other proteins. When introduced into corn cells, cell clumps that had the gene were not colonized as heavily by some representative ear rot fungi compared to cell clumps that did not contain the gene, and also reduced growth rates of representative insects that damage corn ears. Enhanced production of an antifungal compound also occurred, with higher levels associated with higher antifungal activity. This knowledge can be used to guide breeding for insect and ear rot resistance in crop plants, thereby enhancing yield, quality and safety.

Technical Abstract: Determining the genes responsible for pest resistance in maize can allow breeders to develop varieties with lower losses and less contamination with undesirable toxins. A gene sequence coding for a geranyl geranyl transferase-like protein located in a fungal ear rot resistance quantitative trait locus was cloned from an inbred with reported resistance to Fusarium proliferatum and Fusarium verticillioides ear rot. Transgenic expression of the gene in maize callus reduced colonization by these two Fusarium species and also Fusarium graminearum relative to a ß-glucuronidase (GUS) transformant control. Some transformants were also more insect resistant. The more fungal resistant transformant lines produced higher levels of headspace ethanol which were significantly associated with antifungal activity, especially for F. verticillioides. Maize pyruvate decarboxylase appears to have a moiety capable of interacting with the geranyl geranyl transferase, suggesting ethanol production is enhanced due to more efficient transfer of pyruvate through the mitochondrial membrane. Other undetermined mechanisms may also be enhancing resistance of the transformants to the Fusarium fungus, however. This is the first report of the involvement of a geranyl geranyl transferase-like sequence in fungal resistance in plants, and represents a novel mechanism for producing higher yielding and better quality maize.