Author

Ming Zhao

Date of Award

Summer 2021

Document Type

Open Access Thesis

Department

Biological Sciences

First Advisor

Zhengqing Fu

Abstract

In Arabidopsis thaliana, Enhanced Disease Susceptibility1 (EDS1) acts as an indispensable hub in plant immunity and is mainly responsible for plant basal defense, systemic acquired resistance (SAR), increase of endogenous content of salicylic acid (SA) and effector-triggered immunity (ETI). Epigenetic regulators play crucial roles in multiple important cellular processes. As one catalytic core of Polycomb Repressive Complex (PRC2), CURLY LEAF (CLF/SDG1) protein promotes H3K27me3 deposition at specific loci for genes repression. In this work, I found that EDS1 interacted with epigenetic regulators SDG1, SDG9, SDG15, SDG22 and SDG35 in yeast two-hybrid assays. The growth of the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pst.DC3000) was obviously higher in one clf mutant (clf-28-), proposing that CLF has the property of a positive regulator in plant immunity. Confirmation of association of CLF with EDS1 in vivo by BiFC assays indicates the EDS1-CLF protein complex is only located in the nucleus. I also demonstrated that protein levels of EDS1 were severely decreased in clf-28 mutant compared with Col-0 although the relative mRNA level of EDS1 in clf-28 resembled that in Col-0. Apart from epigenetic regulators, mediator member CDK8 was also shown to interact with EDS1 in vitro and in planta. Previous studies demonstrated that CDK8 positively regulates plant defense by upregulating the transcription of SA-associated plant defense genes. Here, I also clarified that CDK8 positively regulates EDS1 protein accumulation.

In plants, Domains Rearranged Methyltransferases 2 (DRM2) is essential for construction of de novo methylation and maintenance of non-CG DNA methylation. Previous research showed that the drm1-2 drm2-2 cmt3-11 (ddc) mutant, which abolished the RNA-directed DNA methylation (RdDM) pathway, had the resistant phenotype after inoculation of the bacteria Pst DC3000 compared with Col-0. On other side of the shield, many gram-negative bacterial pathogens inject effectors into their host’s cells, inducing effector-triggered susceptibility (ETS) or effector-triggered immunity (ETI) in the host immune system. Here, I tested genome-wide pairwise associations of type III effectors with DRM2 and found that HopO1-2, HopAS1, HopAJ2, and HopAG1 interacts with DRM2 in Y2H assays. I have also found that that transgenic Arabidopsis plants overexpressing HopO1-2 and HopAS1 altered abundance on DNA methylation at DRM2 target loci AtSN1 and MEA-ISR.This work will lay the foundation for further exploration of the relationship between DNA methylation and plant immunity.

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