Functional redundancy of structural proteins of the peritrophic membrane in Trichoplusia ni.

Abstract The peritrophic membrane (or peritrophic matrix) (PM) in insects is formed by binding of PM proteins with multiple chitin binding domains (CBDs) to chitin fibrils. Multi-CBD chitin binding proteins (CBPs) and the insect intestinal mucin (IIM) are major PM structural proteins. To understand the biochemical and physiological role of IIM in structural formation and physiological function of the PM, Trichoplusia ni mutant strains lacking IIM were generated by CRISPR/Cas9 mutagenesis. The mutant T. ni larvae were confirmed to lack IIM, but PM formation was observed as in wild type larvae and lacking IIM in the PM did not result in changes of protease activities in the larval midgut. Larval growth and development of the mutant strains were similar to the wild type strain on artificial diet and cabbage leaves, but had a decreased survival in the 5th instar. The larvae of the mutant strains with the PM formed without IIM did not have a change of susceptibility to the infection of the baculovirus AcMNPV and the Bacillus thuringiensis (Bt) formulation Dipel, to the toxicity of the Bt toxins Cry1Ac and Cry2Ab and the chemical insecticide sodium aluminofluoride. Treatment of the mutant T. ni larvae with Calcofluor reduced the larval susceptibility to the toxicity of Bt Cry1Ac, as similarly observed in the wild type larvae. Overall, in the mutant T. ni larvae, the PM was formed without IIM and the lacking of IIM in the PM did not drastically impact the performance of larvae on diet or cabbage leaves under the laboratory conditions.