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ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Crop Bioprotection Research » Research » Publications at this Location » Publication #308913

Research Project: Identification and Validation of Insect and Disease Resistance Mechanisms to Reduce Mycotoxin Production in Midwest Corn

Location: Crop Bioprotection Research

Title: Three sorghum serpin recombinant proteins inhibit midgut trypsin activity and growth of corn earworm

Author
item Johnson, Eric
item Skory, Christopher - Chris
item Naumann, Todd
item Jairajpuri, Mohamad - Jamia Millia Islamia University
item Dowd, Patrick

Submitted to: AGRI GENE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2016
Publication Date: 9/23/2016
Citation: Johnson, E.T., Skory, C.D., Naumann, T.A., Jairajpuri, M.A., Dowd, P.F. 2016. Three sorghum serpin recombinant proteins inhibit midgut trypsin activity and growth of corn earworm. Agri Gene. 2(2016):11-16. doi:10.1016/j.aggene.2016.09.005.

Interpretive Summary: Insect pests of corn continue to cause billions of dollars of losses, and they have developed resistance to insecticidal compounds, including some microbial proteins. Insect damage to corn ears also can increase levels of toxins produced by ear molds, which are harmful to humans and livestock. This situation necessitates searching for new insect resistance molecules. Four proteins coded by sorghum genes were found to inhibit protein digesting enzymes when they were removed from two major insect pests of corn ears. When the proteins were added to test diet, the insects acted as if they were under nutrient stress compared to those fed control diets, and some reductions in growth rate were noted. These results indicate that the genes coding for the sorghum proteins that inhibit insect digestion are candidates that could be combined with other known food plant insect resistance genes through breeding or genetic engineering. More insect resistant plants will reduce economic losses and health hazards caused by these corn ear pests when they feed on corn or other crops.

Technical Abstract: The sorghum (Sorghum bicolor) genome contains at least 17 putative serpin (serine protease inhibitor) open reading frames, some of which are induced by pathogens. Recent transcriptome studies found that most of the putative serpins are expressed but their roles are unknown. Four sorghum serpins were expressed in Escherichia coli and purified using immobilized metal-affinity chromatography to determine if they are involved in insect resistance. Each of the sorghum serpins inhibited in vitro trypsin activity from larval midgut extract of corn earworm (Helicoverpa zea) and fall armyworm (Spodoptera frugiperda). They were also individually added to sorghum leaf insect diet that was fed to fall armyworm larvae. After 4 days, larvae consumed much more of the serpin containing diet than control diet. One serpin-containing diet caused a statistically significant ~20% reduction in the mean weight of larvae compared to those feeding on control diet. Zymography gel electrophoresis of extracts from fall armyworm larvae indicated no unique proteases were induced after feeding on serpin-containing diet. These studies indicate that fall armyworms consume more diet to compensate for reductions in trypsin activity caused by the addition of recombinant serpin, suggesting the insect has counter defenses to the tested serpins.