Degree

Doctor of Philosophy (PhD)

Department

Plant Pathology and Crop Physiology

Document Type

Dissertation

Abstract

Bacterial panicle blight of rice (BPB) caused by Burkholderia glumaeis a major bacterial disease of rice in many rice-producing areas worldwide. Managing the disease is still very difficult due to the lack of effective methods. B. glumaestrains show phenotypic and genomic variations; however, little variation was detected in the known virulence-related genes. In the present study, the complete genome of B. glumae257sh-1, a natural avirulent strain, was sequenced and analyzed. Several spontaneous mutations in the regulatory genes of these avirulent strains were identified. Presumably, the accumulation of these mutations can have a negative effect on the normal function of this protein and be responsible for the avirulence phenotype. The bacterial quorum-sensing (QS) is an essential component for the regulation of major virulence-related functions in B. glumae, but questions remain regarding the function of QS as a global regulator for the pathogenicity, and its strain-specific function. RNA-sequencing was performed to identified potential virulence factors among the quorum sensing (QS) regulon. Among the differentially expressed genes, a serine metalloprotease (prtA) was down-regulated in the QS mutant. A prtA null mutant of 336gr-1, a virulent strain B. glumae, was generated to understand the function of this extracellular protein on rice pathogenesis. Inoculation of rice panicles with a prtAmutant resulted in a significant reduction in disease severity compared with the wild type parent strain, suggesting the requirement of this protease for the full virulence of B. glumae. Moreover, genetic studies comparing two virulent strains of B. glumae, 336gr-1 and 411gr-6, and their respective QS mutants showed that the phenotypic variation previously observed between these two strains is associated with the differential gene regulation dependent upon two primary regulatory systems, TofI/TofR-mediated quorum sensing and QsmR.

Date

6-26-2019

Committee Chair

Ham, Jong H.

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