Roles and Mechanisms of H3.1K27me1 Methyltransferases in Defense Against Virus in Arabidopsis

During the infection process, the host has evolved various mechanisms including DNA methylation and post-translational histone modifications to antagonize geminiviruses. Arabidopsis Trithorax-Related Protein 5 (ATXR5) and ATXR6 deposit H3K27me1 over heterochromatin, which will suppress the DNA re-replication and transposon reactivation to maintain genome stability. Here, we found that atxr5 atxr6 displayed significantly fewer infected plants, milder symptoms, and lower viral titers compared to those in Col-0. Mutations of FAS2 or genes encoding H3.1 resulted in reduced H3.1 and H3.1K27me1 but failed to mimic the suppression of viral DNA replication observed in atxr5 atxr6. Mutations of METHYL-CpG BINDING DOMAIN PROTEIN 9 (MBD9) or Yeast SAC3 HOMOLOG B (SAC3B) in atxr5 atxr6 suppress heterochromatin amplification and TE reactivation. By contrast, mutation of Breast cancer susceptibility gene 1 (BRCA1) slightly enhances above two molecular phenotypes in atxr5 atxr6. Intriguingly, mutations of BRCA1, SAC3B and MBD9 all showed significantly higher numbers of symptomatic plants compared to atxr5 atxr6, which enable us to uncouple the viral resistance of atxr5 atxr6 with transposon reactivation and DNA re-replication. Transcriptome-wide association studies (TWAS) reveled that the mutations of SAC3B, MBD9 and BRCA1 suppressed the enhanced expression of DNA repair-related genes and restored the viral resistance of atxr5 atxr6. In contrast, DNA repair factors such as ATM, ATR, RAD51, and RPA1A were required for efficient viral DNA amplification. RAD51 and RPA1A directly bound to the viral genome to promote virus amplification. Combined with the fact that increased amount of DNA double-strand breaks (DSBs) in atxr5 atxr6, we hypothesized a competition between host and viral genomes for DNA repair factors. We performed genome wide chromatin immunoprecipitation-sequencing (ChIP-seq) to test our hypothesis. Interestingly, we observed a substantial increase of RAD51 and RPA1A occupancy at the heterochromatin regions including ribosomal DNA (rDNA) and non-coding RNAs (ncRNAs) in atxr5 atxr6 vs Col-0 under both mock and virus-treated conditions. Virus infection compromised the RAD51 occupancy at defense-related genes and accumulation of transcripts in Col-0 whereas enhanced the RAD51 occupancy at defense-related genes and accumulation of transcripts in atxr5 atxr6 vs Col-0. Breast cancer 1 (BRCA1), HOP2, and B1 type cyclin-dependent protein kinase CYCB1; promote the loading of RAD51 onto the unstable host genome and defense-related genes in atxr5 atxr6 but suppressed the loading of RAD51 onto virus genome in atxr5 atxr6. As a consequence, mutations of BRCA1, HOP2 and CYCB1 enhanced the RAD51 occupancy at virus genome and restored the viral resistance of atxr5 atxr6. Our results uncover a novel mechanism in which unstable genome induced by decreased H3K27me1 could activate the DNA repair pathway and retain DNA repair-related proteins onto the host genome to fine-tune plant immunity and restrict virus replication.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Molecular and Environmental Plant Sciences

Grantor

Texas A&M University

Year dc:date.issued

2022

Author dc:creator

• Wang, Zhen

Advisor dc:contributor.advisor

• Zhang, Xiuren

Committee members dc:contributor.committeemember

• Sachs, Matthew S.
• Devarenne, Timothy
• Koiwa, Hisashi

• Biology, Plant Physiology
• Biology, Virology

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/1969.1/1595961

OAI record oai:identifier

https://oaktrust.library.tamu.edu/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Aoaktrust.library.tamu.edu%3A1969.1%2F1595961