Proteomic Analysis Of Maize Leaf Tissues From Inbred Lines Resistant And Susceptible To Fall Armyworm, Spodoptera frugiperda (J.E. Smith)

Open Access
Author:
Kooner, Ramneek
Graduate Program:
Plant Biology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
October 31, 2008
Committee Members:
  • Dawn S Luthe, Thesis Advisor
Keywords:
  • Proteomics
  • Maize
  • Fall Armyworm
  • 2-D DIGE
Abstract:
The main focus of this study was to gain deeper understanding of maize resistance to fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), which is a serious pest in the southern United States. This study is primarily aimed at investigating the protein complement in the maize mid-whorl, which is the main larval feeding site. In the resistant genotype Mp708, a unique, extracellular, 33-KDa cysteine protease (Mir1-CP) accumulates in whorl in response to insect feeding, which retards the larval growth by attacking the mid-gut region of the insect. On the other hand, the susceptible inbred Tx601 does not retard larval growth when compared to Mp708. In this study, our objectives were 1) to identify differentially expressed proteins in the whorls of resistant and susceptible genotypes before and after FAW feeding, and 2) to identify proteins that are up/down-regulated in response to FAW feeding in resistant and susceptible genotypes. Comparative proteomics analysis, employing the use of gel-based tool, two-dimensional Difference In-Gel Electrophoresis (2-D DIGE) coupled with MS/MS MALDI-TOF, was used. Our results show that the resistant genotype had elevated levels of antioxidant/detoxifying enzymes, which are induced during abiotic stress compared to the susceptible genotype after infestation. The stress-related proteins expressed in the resistant genotype such as glutathione S-transferase (GST) and S-adenosylmethionine synthetase have shown to be induced by jasmonic acid (JA) (Xiang et al., 1996); and it is already established that Mp708 resistant genotype constitutively has elevated levels jasmonic acid. So higher levels GSTs and S-adenosylmethionine synthetase in the resistant inbred implies higher induction of jasmonic acid after infestation. On the other hand the susceptible genotype primarily expressed heat shock proteins instead of other stress proteins. Proteomic analyses to elucidate interactions within each genotype in response to larvae were also performed. Interestingly, the proteins that were up-regulated in resistant genotype after infestation were stress related proteins and the most important proteins that were down-regulated included photosynthetic proteins such as Rubisco small subunit etc. In case of the susceptible genotype, the proteins that were up-regulated by larval infestation involved mostly the metabolic proteins and those down-regulated included stress-related proteins. Proteomic approaches detected and identified sets of proteins from mid-whorl region of maize that are possibly engaged in the defense mechanism to larval infestation. For this study we conclude that the mechanism of resistance/susceptibility is rather complex and involves a broad range of proteins, where the expression of stress-related proteins is very important to maintain resistance.