Theses and Dissertations

Di Ren

Issuing Body

Mississippi State University

Advisor

Dawe, Angus L.

Committee Member

Perkins, Andy D.

Committee Member

Gordon, Donna M.

Committee Member

Brown, Matthew W.

Date of Degree

8-10-2018

Document Type

Dissertation - Open Access

Major

Biological Sciences

Degree Name

Doctor of Philosophy

College

College of Arts and Sciences

Department

Department of Biological Sciences

Abstract

Cryphonectria parasitica is the causal agent of chestnut blight, which devastated the American Chestnut tree population in the early 20th century. The discovery of hypoviruses that reduce the severity of the chestnut blight infection offers the potential for biological control. However, the spread of the hypoviruses is hampered by a diverse genetically controlled nonself-recognition system, vegetative incompatibility (vic). CPVIB-1 was identified as a transcription regulator playing an important role in the programmed cell death response to this stimulus. In this study, we have found that CPVIB-1 is ubiquitin-decorated which might lead to its degradation in the proteasome pathway. RNA-Seq and ChIP-Seq were used to further explore the downstream targets of CPVIB-1 that mediate the various metabolic changes that lead to the altered phenotype of the Δcpvib-1 mutant. Due to inaccuracies in the prior annotation, we performed a genome re-annotation to improve the accuracy using a MAKER2-two-pass pipeline. To validate the improvement a second pipeline, PEPA, was developed to compare quality metrics between the old and new annotations. Approximately 1/3 of the original annotations from 2009 were found to be inaccurate. Experimental confirmation by testing 27 predicted genes using a diagnostic PCR protocol to differentiate between prior and new transcript structures showed that over 80 % of tested genome locations supported for the new annotation. Using rapamycin treatment to mimic stimulation of the vic response and applying the RNA-seq and ChIP-seq data to this new information, we found that CPVIB-1 is related to TOR signaling pathways, promoting autophagy and the proteasome pathway, but repressing carbon metabolism, protein and lipid biosynthesis. In depth analysis of CPVIB-1-bound DNA targets showed that this protein is a member of the GAGA regulator family, a group of multifaceted transcription factors with diverse roles in gene activation and repression, maintenance of mitosis, and cell development. Following treatment with rapamycin the recognition sequence bound by CPBVIB-1 was altered leading to the regulation of different suite of genes with diverse metabolic functions. Ultimately, we have developed a revised model of TOR signaling pathway where TORC1 and TORC2 signaling pathways are connected by the action of CPVIB1.

URI

https://hdl.handle.net/11668/21013

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