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United States Department of Agriculture

Agricultural Research Service

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Research Project: Disease Defense Responses Signaling in Maize

Location: Chemistry Research Unit

Project Number: 6615-21000-011-00
Project Type: Appropriated

Start Date: Jul 02, 2013
End Date: Jul 01, 2018

Objective:
1. Characterize early signaling events and components that mediate recognition of biotic attack in maize. 1.A. Elucidation of the roles of individual maize Plant Elicitor Peptides in responding to biotic attack. 1.B. Characterization of ZmPEPR receptor candidate signal ansduction interactions and specificity. 2. Identify and manipulate signal transduction mechanisms that regulate maize defense metabolism. 2.A. Evaluation of transgenic manipulation of Plant Elicitor Peptide gene expression as a strategy for improving maize resistance to biotic attack. 2.B. Determination of chemotype for resistant vs susceptible maize varieties and investigation of whether chemical constituents contribute to phenotype.

Approach:
To determine if maize defense responses are mediated by members of the Pep family we will examine expression of individual ZmPROPEP genes in different tissues after biotic challenge. Leaves and stems will also be treated with the herbivore-derived elicitors. Expression of each ZmPROPEP gene will be ascertained via qRT-PCR accompanied by characterization of defenses elicited by individual ZmPep peptides. Time course studies will be conducted to determine levels of hormones, transcripts, benzoxazinoid and terpenoid phytoalexins using qRT-PCR, GC-MS and HPLC analyses. To understand interactions between ZmPeps and the ZmPEPR receptors, we will clone and heterologously express ZmPEPR1 and ZmPEPR2 in Arabidopsis thaliana plants and Nicotiana tabacum cells. Interactions will be examined in transgenic N. tabacum suspension culture cells by monitoring changes in extracellular pH. Arabidopsis expressing ZmPEPR candidates will be used to ascertain how receptor activation translates into downstream responses. We will measure responses of transgenic plants treated with maize peptides by measuring emission of ethylene and metabolic changes at 1, 4 and 24 hr post-treatment. We will examine ZmPEPR receptor expression and localization in maize by qRT-PCR monitoring of relative transcript abundance at different stages of development and in response to fungal infection, herbivory or elicitors. Expression of the two receptors will be compared in maize inbreds that respond poorly to Pep elicitation versus strong responders. We will generate transgenic plants carrying ZmPEPR promoter:ß-glucoronidase fusions to examine expression at a more discrete organ level. To evaluate transgenic manipulation of PROPEP gene expression to improve maize resistance to biotic attack we will generate transgenic maize lines expressing ZmPROPEP1 genes. We will assess ZmPROPEP transgene effects on resistance to insects and pathogens in the greenhouse. Leaf blight and stalk rot symptoms will be measured using image analysis and cellular ion leakage. Ear rot assays will be scored upon harvest. Herbivore resistance will be evaluated by visual rating of damage and measurements of larval growth rates. We will assess basal and induced immune responses in transgenic lines through measurement of defense-related hormones, metabolites and transcripts

Last Modified: 9/23/2014
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