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Document Type

Dissertation - University Access Only

Award Date

2014

Degree Name

Doctor of Philosophy (PhD)

Department

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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