Dissecting the role of H2A.Z and chromatin modification patterns in transcriptional regulation in Arabidopsis thaliana: insights from cross-species comparisons and stress response analyses Open Access
Silver, Brianna (Summer 2026)
Abstract
While eukaryotic transcriptional regulation utilizes many conserved chromatin mechanisms, species- and context- specific regulatory features allow for widely varied outputs. By leveraging both cross-species comparisons and inducible stress responses, this dissertation seeks to deepen understanding of the role of the universal histone variant H2A.Z in both transcriptional initiation dynamics and in modulating gene transcription rate. First, cross-species analyses of transcriptional initiation directionality across Arabidopsis thaliana, Drosophila melanogaster, and humans revealed that while animals frequently initiate transcription of protein-coding genes bidirectionally, Arabidopsis shows predominantly unidirectional transcription initiation. This patterning correlates with the distribution of H2A.Z, as animals often have H2A.Z at both the -1 and +1 nucleosomes flanking the transcription start site of actively transcribed genes, whereas in Arabidopsis and other plants, it is generally found only at the +1 nucleosome. This suggests a possible role for H2A.Z in driving and/or reinforcing transcriptional directionality. Next, cross-species functional analysis of H2A.Z between humans and Arabidopsis reveals that h2a.z null plants can be phenotypically and molecularly rescued by either human H2A.Z.1 or H2A.Z.2. Because human and Arabidopsis H2A.Z differ most substantially in the N-terminal tail region, and sequential truncation mutants in Arabidopsis are also phenotypically normal under optimal growth conditions, these findings suggest that the N-terminus of Arabidopsis H2A.Z is largely dispensable for development of the plant. Finally, we investigated whether the N-terminal tail of Arabidopsis H2A.Z is important for processes requiring rapid transcriptional changes, such as stress responses. H2A.Z N-terminal mutants (complete tail deletion or lysine-to-arginine substitutions) displayed impaired development when germinating under abscisic acid (ABA) exposure. Transcriptome analyses uncovered that although these mutants can initiate an ABA response, they display reduced transcriptional buffering, with responsive genes exhibiting exaggerated magnitudes of up- and down-regulation. Taken together, H2A.Z appears to play important roles in transcriptional regulation across species, from influencing transcriptional initiation directionality to modulating stress response. These studies demonstrate the importance of comparative biology and illustrate that while conserved chromatin machinery provides a common functional framework, species- and context-specific features provide fine-tuning mechanisms that ultimately shape transcriptional output.
Table of Contents
Table of Contents
Chapter 1:……………………………………………………………………………………….1
Introduction
Chapter 2:……………………………………………………………………………………….15
Differences in transcription initiation directionality underlie distinctions between plants and animals in chromatin modification patterns at genes and cis-regulatory elements
Chapter 3:…………………………………………………………………………………….....50
Replacement of Arabidopsis H2A.Z with human H2A.Z orthologs reveals extensive functional conservation and limited importance of the N-terminal tail sequence for Arabidopsis development
Chapter 4:………………………………………………………………………………………93
The N-terminal tail of H2A.Z modulates the magnitude of transcriptional responses to abscisic acid in Arabidopsis thaliana
Chapter 5:……………………………………………………………………………………...150
Discussion
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Dissecting the role of H2A.Z and chromatin modification patterns in transcriptional regulation in Arabidopsis thaliana: insights from cross-species comparisons and stress response analyses () | 2026-07-02 15:31:27 -0400 |
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