Isolation and characterization of elicitors from the oral secretion of lepidoptera larvae
Insect herbivory on plants is a complex interaction between several organisms, various chem-ical factors and fine tuned plant signaling cascades. The oral secretion (OS) from insect lar-vae contains a “pool” of chemicals which could trigger diverse plant defense reactions. Espe-cially, the oral secretion from lepidopteran larvae showed channel-forming activity in the black lipid membrane (BLM) assay, which was common for several lepidopteran species. Therefore this PhD work mainly concentrated on the discovery of new elicitor(s) which have the channel-forming activity, and further investigate the corresponding functions in plant de-fense. Here, a porin like protein (PLP) has been partially purified through diverse column chromatography and identified as a channel-forming compound present in the OS of S. littoralis larvae. Following the BLM-guided fractionation of 10 mL OS (collected from 500 larvae in the 4th instar stage) and proteomic analysis of several BLM active fractions, the identified peptides (ATIAGTYAFGPAK and TDAYFNLAYAK) were matched to the porin type protein derived from Gram-negative Ralstonia pickettii 12J by stringent database search-ing of MS/MS spectra (MASCOT) and homology-based approach (de novo MS BLAST). Due to the limited amount of OS, it was impossible to get the pure PLP from the final active fraction. Fortunately, the commercially available porin α-hemolysin (α-HL, 41) showed comparable BLM activity compare to the crude oral secretion and active fractions. This fur-ther confirmed the interpretation of proteomic data and indicated that the porin-like protein (PLP) from OS is one of the factors responsible for the channel-forming activity.