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Submitted to: Journal of Plant Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/26/2015 Publication Date: 12/10/2015 Publication URL: https://handle.nal.usda.gov/10113/62362 Citation: Dowd, P.F., Johnson, E.T. 2015. Maize peroxidase Px5 has a highly conserved sequence in inbreds resistant to mycotoxin producing fungi which enhances fungal and insect resistance. Journal of Plant Research. 129(1):13-20. doi: 10.1007/s10265-015-0770-3. Interpretive Summary: Corn ear damaging insects and molds cause millions of dollars in damage each year. Some ear molds also produce toxins that are harmful to people and animals. Many mold resistant corn lines have been identified, but the reason for resistance has not been determined. The sequence of a candidate resistance gene was sequenced in several resistant and susceptible corn inbreds. The common sequence from the resistant inbreds that was introduced in to corn cells caused more of the protein to be made and caused cell clumps to be more resistant to the ear feeding insects and an ear mold fungus compared to control material. Breeding of corn to make more of the resistance protein should lead to improved yields and safer corn for humans and animals. Technical Abstract: Mycotoxin presence in maize causes health and economic issues for humans and animals. Although many studies have investigated expression differences of genes putatively governing resistance to producing fungi, few have confirmed a resistance role, or examined putative resistance gene structure in more than a couple of inbreds. The pericarp expression of maize Px5 has previously been associated with resistance to Aspergillus flavus growth and insects in a set of inbreds. Genes from 14 different inbreds that included ones with resistance and susceptibility to A. flavus, Fusarium proliferatum, F. verticillioides, and F. graminearum and/or mycotoxin production were cloned using high fidelity enzymes, and sequenced. The sequence of Px5 from all resistant inbreds was identical, except for a single base change in two inbreds, only one of which affected the amino acid sequence. Conversely, the Px5 sequence from several susceptible inbreds had several base variations, some of which affected amino acid sequence that would potentially alter secondary structure, and thus enzyme function. The sequence of the maize peroxidase Px5 common to inbreds resistant to mycotoxigenic fungi was overexpressed in maize callus. Callus transformants overexpressing the gene caused significant reductions in growth for fall armyworms, corn earworms, and Fusarium graminearum compared to transformant callus expressing ß-glucuronidase. This information suggests that differences in sequence of resistance genes can influence protein product structure and potentially explain some of the susceptibility or resistance of maize inbreds. |
