A maize hydrolase with activity against maize insect and fungal pests

Authors: Dowd, Patrick; Naumann, Todd; Johnson, Eric; Price, Neil

Submitted to: Plant Gene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2019
Publication Date: 11/14/2019
Citation: Dowd, P.F., Naumann, T.A., Johnson, E.T., Price, N.P.J. 2020. A maize hydrolase with activity against maize insect and fungal pests. Plant Gene. 21:100214. https://doi.org/10.1016/j.plgene.2019.100214.
DOI: https://doi.org/10.1016/j.plgene.2019.100214

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 postulated role for the protein coded by the gene was to degrade a sugar polymer found in the skin of fungi and insects. The protein, when produced by yeast, was active against maize insect and fungal pests, and degraded fatty substrates but not those associated with the sugar polymer. When introduced into corn cells, cell clumps that had the gene reduced growth of maize pest caterpillars and representative ear rot fungi compared to cell clumps that did not contain the gene. Levels of the protein in cell clumps were associated with the degree of reduced growth by insects and fungi. 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: A gene annotated as a chitinase-like protein that occurred in a QTL for fungal resistance was cloned from a maize inbred with Fusarium proliferatum/verticillioides resistance. The protein sequence was similar to type III chitinases and homologous proteins without chitinase activity generally referred to as narbonins or chitolectins. The gene was expressed in Pichia pastoris, and the resulting protein was purified and examined for different types of activity. The protein did not hydrolyze chitin substrates, or 4-nitrophenyl sugars, but did hydrolyze 4-nitrophenyl acetate and 4-nitrophenyl palmitate. It significantly retarded the growth of first instar fall armyworms (Spodptera fruigiperda) and significantly enhanced the activity of miconazole nitrate toward F. graminearum. The gene was biolistically introduced into maize BMS callus and the transgene was detectible by PCR. Some transformant lines significantly reduced corn earworm, fall armyworm, F. graminearum, F. proliferaturm and F. verticillioides growth compared to GUS transformed control callus. When transformed callus protein extracts were separated by native polyacrylamide gel electrophoresis, a band of 4-nitrophenyl acetate activity was found in bioactive callus that was not present in GUS control callus. Although the true target of the hydrolase is not known, it does appear to play a role in resistance to pests of maize and appears to be a previously unreported type of resistance mechanism.