MAIZE DEFENSE RESPONSES AND STRATEGIES AGAINST ABOVEGROUND AND BELOWGROUND INSECTS

open_access
Open Access
Author:
Castano-Duque, Lina M
Graduate Program:
Plant Biology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 02, 2017
Committee Members:
Dawn S. Luthe, Dissertation Advisor/Co-Advisor
Dawn S. Luthe, Committee Chair/Co-Chair
Kathleen M. Brown, Committee Member
Réka Albert, Committee Member
Mary Barbercheck, Outside Member
Keywords:
maize
Diabrotica virgifera virgifera
Spodotera frugiperda
plant-insect interactions
plant defenses
proteomics
network biology
Abstract:
This dissertation had three main projects. In the first project we studied insect resistance traits against the root herbivore, western corn rootworm (WCR, Diabrotica virgifera) in the insect resistant maize genotype, Mp708 and its susceptible parent, Tx601 using biomechanical, root anatomy, molecular and biochemical analyses. These two maize genotypes differ in susceptibility to fall armyworm (FAW, Spodoptera frugiperda), WCR, and corn leaf aphid (CLA, Rhopalosiphum maidis). The data suggested that Mp708 is more resistant to WCR than Tx601 due to strong nodal roots, constant root growth under infestation, constitutive and induced expression of ribosomal protein 2 (rip2), terpene synthase 23 (tps23) and maize insect resistant cysteine protease-1 (mir1), as well high constitutive and inducible levels of MIR1-CP protein, jasmonic acid (JA) and caryophyllene. We concluded that Mp708 showed resistance and antibiosis against WCR and could be used as a model to explore the wide variety of mechanisms and traits involved in plant defense responses. In the second project we explored the use of innovative proteomic and network analyses to understand the global defenses deployed by maize plants infested with the root-feeder, WCR. Using the relatively new technique that employs 10-plex tandem mass spectrometry tags (TMT), we measured protein abundance changes in roots and leaves in response to these pest because metabolic changes in response to herbivory include a wide variety of mechanisms that enable the plant to survive. TMT data were analyzed by using a protein co-abundance and protein-protein interaction (PPI) networks. We detected 4878 proteins of which 863 had significant changes under WCR infestation. Proteins with higher abundance during WCR infestation were involved in the JA pathway and included lipoxygenase 5 (lox5), allene oxidase synthase 1 (aos1), and 12-oxophytodienoate reductase 2 (opr2). Other high abundance proteins during infestations were part of biosynthesis and signaling pathways for proteases of serine/cysteine type, abscisic acid, reactive oxygen species, and ethylene (ET). We validated changes in these pathways by analyzing the expression of key genes in each, total protease activity, cysteine and serine-type protease inhibition, JA and ET production. Our data showed promising differences between tissue-specific defense responses in leaves and roots of plants infested by WCR. Also, we suggested a dual insect and microbial plant stress response and postulated that roots infested with WCR are under constant microbial pressure due to the interactions in rhizosphere. In the third project we studied Mp708 tissue-specific responses to FAW by using the same proteomics and analysis techniques used for the second project. In addition we merged our proteomics network data with QTL known regions of resistance in Mp708 against FAW. We detected 4675 proteins of which 794 had significant changes under FAW infestation. Our analyses suggested an increase in the JA biosynthesis, REDOX changes in the glutathione and ascorbate pathways, and increase in ABA and ET biosynthesis and signaling. Infested leaf tissues showed high abundance and enrichment of proteinase inhibitors, cysteine proteases and peroxidases, these are well known plant defense proteins. Validations of total peroxidase activity showed an early activity spike in leaves of Mp708 and no change in the roots during FAW infestation , suggesting an early ROS signaling event that might not involve peroxide or an increase in quinone production mediated by peroxidases. Gene expression and phytohormone analyses showed that JA biosynthesis was activated in leaves and ET production increased only in roots, furthermore, JA and ET appears to control local MIR1-CP and RIP2 accumulation, and ET could be a key regulator of MIR1-CP systemic accumulation. These findings open up new routes in the hormonal control of local and systemic defense signaling that could be similar for other defense proteins and secondary compounds. Using the protein-correlation network with the known QTL regions, we found some proteins that might be part of the defense responses and tolerance against FAW that are involved in plant defenses, development and growth. Growth analyses determined that the insect susceptible maize genotype, Tx601, grew less in height and total root length during FAW infestation. We concluded that Mp708 defense mechanisms could involve lower trade-offs between plant growth and defense responses. We have established an analysis pipeline for proteomics data that includes network biology approaches that can be used with different types of “omics” data from a wide variety of organisms to detect tissue-specific defense responses.

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