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Document Type

Dissertation - University Access Only

Award Date

2014

Degree Name

Doctor of Philosophy (PhD)

Department / School

Biology and Microbiology

First Advisor

Yang Yen

Abstract

Fusarium graminearum is the primary causative pathogen of Fusarium Head Blight in wheat. To identify genetic components behind the host-pathogen interaction, we used FHB-resistant wheat cultivar Sumai 3, FHB-susceptible wheat landrace Y1193-06 and F. graminearum isolate 4 in this study. Through eQTL analysis, we functionally associated one gene, WFhb1_c1 (Wheat Qfhb1 candidate gene 1), with Qfhb1 and two genes, WFI_6BL1 and WFI_6BL2 (Wheat-F. graminearum interacting genes 1 and 2), with Qfhb6BL. WFI_6BL1 was annotated as a 13-lipoxygenase gene and WFI_6BL2 as a PR-4 like protein, and thus both are involved in JA-mediated resistance pathways. Knocking down of WFhb1_c1 with a virus-induced gene silencing technology in spikes of Sumai 3 during flowering stage turned the highly FHB-resistant cultivar into an FHB-susceptible one. Therefore, WFhb1_c1 has been confirmed as a genic component of Qfhb1, playing a key role in FHB resistance in wheat. Our expression assay with RTqPCR revealed that WFhb1_c1 was functionally suppressed up to the ~60 hours after F. graminearum infection in Y1193-06 but not in Sumai 3. To further study the regulation mechanism of WFhb1_c1, we made four small RNA libraries from wheat spikes of a near-isogenic pair differing Qfhb1 either with or without F. graminearum challenge, respectively. A small RNA library of cultured F. graminearum also was constructed and sequenced. From these libraries, we identified four novel microRNAs in wheat and seven microRNA-like RNAs and 44 silencing RNAs in F. graminearum. Interestingly, knocking down of the Dicer 2-like gene in F. graminearum reduced the pathogen‘s aggressiveness, leading to non-suppression of WFhb1_c1 early in FHB pathogenesis and thus to poor FHB development in Y1193-06. Therefore, our data suggested that: 1) WFhb1_c1 is a key genic component of Qfhb1; 2) regulation of WFhb1_c1‘s expression early in the FHB pathogenesis, possibly by F. graminearum small RNAs, is a decisive factor of FHB resistance/susceptibility; 3) Qfhb6BL makes its contribution to FHB resistance via the JA-mediated pathways; 4) biotrophic stage of FHB pathogenesis is critical for wheat to establish its defense mechanism and; 5) small RNAs also exist in F. graminearum and could possibly be utilized as virulence factors to enhance its pathogenicity.

Library of Congress Subject Headings

Fusarium diseases of plants
Wheat -- Disease and pest resistance -- Genetic aspects

Description

Includes bibliographic reference (pages 105-133)

Format

application/pdf

Number of Pages

227

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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