Maize Defense Responses to Caterpillars at the Molecular, Phenotypic and Ecological Scales

Open Access
Author:
Jin, Shan
Graduate Program:
Plant Biology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 01, 2017
Committee Members:
  • Dawn S. Luthe, Dissertation Advisor
  • Dawn S. Luthe, Committee Chair
  • Surinder Chopra, Committee Member
  • Claude dePamphilis, Committee Member
  • Gary W. Felton, Outside Member
Keywords:
  • maize-insect interaction
  • maize NAM founder lines
  • fall armyworm
  • cover crop
  • black cutworm
  • maize insect resistance 1
Abstract:
Maize (Zea mays ssp. mays), one of the most important crops worldwide, has to face attack from numerous insects during its life cycle in the field. The major pests of maize include caterpillars, beetles, aphids, and thrips. The aim of the dissertation was to study maize defense responses to caterpillars at the molecular, phenotypic and ecological scales. More specifically, maize defense responses to fall armyworm (FAW, Spodoptera frugiperda) and black cutworm (BCW, Agrotis ipsilon) in the Order of Lepidoptera were investigated in various experimental settings. Chapter 2 assessed maize defense responses to FAW in the nested association mapping (NAM) founder lines, and illustrated possible resistance mechanisms. Insect bioassays indicated that the constitutive defense of the 25 founder lines fall into a continuum. High levels of rip2 and mpi transcript expression and RIP2 protein accumulation in resistant genotypes correlated with their high constitutive defenses to FAW. There was a correlation between rip2 expression levels and RIP2 accumulation upon FAW herbivory in the diverse maize inbred lines. Chapter 3 focused on the soil-mediated cover crop effect on corn defense response to BCW, and linked the molecular aspects of corn defense responses to agroecosystem and farming management practices. BCW grew better when corn plants obtained adequate amount of N from soil provided by cover crops, so cover crops benefited both corn plants and BCW at the phenotypic level. Secondly, cover crops increased the expression of several corn defense genes to deter BCW herbivory at the molecular level. Therefore, the relationship of cover crops and corn defense responses to BCW is not a simple linear relationship. The Appendix Chapter investigated an important herbivore defense gene maize insect resistance 1 (mir1) expression in 23 NAM founder lines, and it was found that maize natural sequence polymorphism affects the expression of mir1. 23 maize NAM founder lines including B73 did not express mir1 in their whorls before or after FAW infestation and the presence of the 4789 bp region including a CACTA transposable element in mir1 promoter of these lines is likely one of the regulatory sequences controlling mir1 expression in diverse maize lines whorls. The second regulatory sequence controlling mir1 expression is an inverted-repeat transposable element (MITE) in Mp708 mir1 intron three. This dissertation primarily tackled the question of how maize plant protects and defends itself against caterpillars within systems of various scales. It has added to the basic scientific knowledge of maize and insect interactions, and provided a fresh view of key components not only as separate research objects, but also from a holistic perspective to understand the hidden mechanisms.