Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Jeffrey J Stuart

Committee Member 1

Catherine A Hill

Committee Member 2

Daniel B Szymanski

Committee Member 3

Greg J Hunt

Committee Member 4

Steven R Scofield

Abstract

The Hessian fly - wheat system is a well-known model of gene-for-gene interac- tion between host plants and parasitic insects. The Hessian fly uses secreted effector proteins to control susceptible host plant physiology, transforming the plant cells in a nutritive tissue to support the developing insect larva. HF-resistant wheat cultivars employ resistance (R) proteins to perceive the insect avirulence effectors (Avr) and display defensive immune responses. This study is focused in the discovery and functional analyses of insect effector-encoding genes. Chapter one of this thesis offers an introduction about the molecular basis of HF-wheat interactions. In Chapter two, I present the genetic mapping of HF Avr genes vH6, vHdic and vH5 using a genome- wide strategy. Differences in SNP-allele frequencies obtained from whole-genome pool sequencing positioned vH6 and vHdic on two different genomic regions in the long arm of chromosome X2. vH5 was mapped on 1.3Mb of a proximal genomic region of chromosome A2 (Scaffold A2.7). Gene expression analyses permitted to identify two vHdic candiate genes. In chapter three, I propose that HF SSGP71 family members encode effectors that structurally resemble E3-ubiquitin-ligases. SSGP71 proteins contain putative F-box and leucine rich repeats (LRR) domains. Yeast 2-hybrid experiments showed that SSGP71 members interact with host plant Skp1-like proteins. In chapter four, I use bacterial T3SS-based delivery of proteins into plants to test candidate HF effector-encoding genes. Candidate vH13 failed to induce plant immune responses in H13-resistant wheat leaves when carried by Pseudomonas fluorescens. However, experiments with the plant pathogen Burkholderia glumae carrying candidates vH13 or vH16 suggest they might interfere with plant immunity in Nicotiana spp.

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