| Summary: | <p>The peritrophic matrix (PM) lines the insect midgut and is composed of chitin and protein. It is required for organization of digestion and for protection of epithelial cells from mechanical damage, pathogens, and toxins. The PM of <i>Mamestra configurata</i> (Lepidoptera: Noctuidae), bertha armyworm, a serious pest of cruciferous oilseed rape, was studied. The multilayered PM is delaminated from the anterior midgut epithelium during molting Phase II by periodic pulses and degraded during the molting Phase I stage. These events are controlled by chitin synthase-B, and chitinolytic enzymes, such as chitinase and β-<i>N</i>-acetylglucosaminidase. Eighty-two PM proteins were identified and classified as: i) peritrophins, ii) enzymes and iii) other proteins. Peritrophins were further classified as simple, binary, complex and repetitive according to their structural organization and phylogenetic analysis of peritrophin A domains. The expression of most genes encoding PM proteins was specific to the midgut and independent of larval feeding status, developmental stage, or PM formation.</p>
<p>This study includes the first report of chitin deacetylase (CDA) activity in the insect midgut suggesting that the PM may contain chitosan. Digestive enzymes, such as insect intestinal lipases (IILs) and serine proteases were also associated with the PM. The IIL genes differed in their expression during larval development; however, serine protease genes were expressed continuously and serine protease activity was present in the midgut of feeding and nonfeeding stages. <i>M. configurata</i> IIM4, a complex peritrophin, was susceptible to degradation by Mamestra configurata nucleopolyhedrovirus-A challenge, as the first evidence of IIM degradation by an alphabaculovirus enhancin. <i>M. configurata</i> IIM2, a binary peritrophin, was unaffected by baculoviral challenge and such resistance of an IIM has not been reported previously. The current study is also the first demonstration of silencing by RNA interference (RNAi) of any gene encoding a PM protein, in this case <i>M. configurata</i> CDA1 (McCDA1) and McPM1. In addition, both <i>in vitro</i> and <i>per os</i> feeding experiments revealed <i>McCDA1</i> silencing starting at 24 or 36 hours posttreatment, as one of the most successful demonstrations of RNAi in a lepidopteran.</p>
|
|---|
