Deciphering the transcriptional regulation and response of barley to obligate fungal biotroph invasion

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Moscou, Matthew
Major Professor
Roger P. Wise
Julie A. Dickerson
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Plant Pathology and Microbiology
The Department of Plant Pathology and Microbiology and the Department of Entomology officially merged as of September 1, 2022. The new department is known as the Department of Plant Pathology, Entomology, and Microbiology (PPEM). The overall mission of the Department is to benefit society through research, teaching, and extension activities that improve pest management and prevent disease. Collectively, the Department consists of about 100 faculty, staff, and students who are engaged in research, teaching, and extension activities that are central to the mission of the College of Agriculture and Life Sciences. The Department possesses state-of-the-art research and teaching facilities in the Advanced Research and Teaching Building and in Science II. In addition, research and extension activities are performed off-campus at the Field Extension Education Laboratory, the Horticulture Station, the Agriculture Engineering/Agronomy Farm, and several Research and Demonstration Farms located around the state. Furthermore, the Department houses the Plant and Insect Diagnostic Clinic, the Iowa Soybean Research Center, the Insect Zoo, and BugGuide. Several USDA-ARS scientists are also affiliated with the Department.
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Obligate fungal biotrophs have co-evolved with their plant hosts, a direct result of an intimate interaction that protects the integrity of the plant during pathogenesis, allowing it to obtain essential nutrients. To restrict the establishment of pathogen colonization, plants have evolved complex regulatory mechanisms to control the defense response, the most extreme of which involves Resistance (R) gene-mediated programmed cell death. While it is known that de novo gene expression and subsequent protein synthesis are required for several cell death programs, the primary transcriptional targets of R gene-mediated responses are unknown. Two alternative approaches were used to identify these transcriptional targets. The first approach uses a time-course microarray experiment that contrasts wild-type and loss-of-function mutant alleles of the Mla (powdery mildew) R gene to identify transcripts that distinguish incompatibility from compatibility. Earlier expression and stronger transcriptional responses were observed in compatible plants at 20 hours after inoculation, though this reaction diminished at later time points. In contrast, incompatible interactions exhibited a time-dependent strengthening of the transcriptional response, with increases in both fold change and total number of genes differentially expressed. These results implicate MLA as a repressor of early gene expression response and provides further evidence for a link between basal and R gene-mediated resistance. The second approach uses natural variation present in a doubled-haploid population to identify the regulatory hierarchy of gene expression during the interaction of barley and stem rust. A trans-eQTL hotspot is not associated with the R gene Rpg-TTKSK, but instead an inoculation-dependent expression polymorphism in Adf3 implicates it as a candidate susceptibility gene. In contrast, co-localization of a trans-eQTL hotspot with an enhancer of R gene-mediated resistance to stem rust associates the suppression of gene expression with enhanced resistance. Lastly, Blufensin1 (Bln1) is used as a case study for functional analysis using gene expression, structural features, and phenotype. Although greater expression of Bln1 was previously associated with incompatibility, virus-induced gene silencing and transient overexpression implicates that Bln1 negatively impacts defense. Collectively, these studies suggest that our understanding of gene expression and its phenotypic consequences is more complex than previously thought.

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Fri Jan 01 00:00:00 UTC 2010