Histone Variants in Development and Diseases

Eukaryotic genomic DNA is highly packaged into chromatin by histones to fit inside the nucleus. Other than the bulk packaging role of canonical histones with an expression peak at S phase and replication-coupled deposition, different histone variants have evolved distinct regulatory mechanisms for their expression, deposition and functional implications. The diversity of histone variants results in structural plasticity of chromatin and highlights functionally distinct chromosomal domain, which plays critical roles in development from a fertilized egg into a complex organism, as well as in aging and diseases. However, the mechanisms of this fundamental process are poorly understood so far. It is of particular interest to investigate how the variants are incorporated into chromatin and mark specific chromatin states to regulate gene expression, and how they are involved in development and diseases. In this review, we focus on recent progress in studies of epigenetic regulation of three extensively investigated variants including H2A.Z, macroH2A and H3.3, and their functional implications in development and diseases.

H2A Variants in Arabidopsis: Versatile Regulators of Genome Activity

The eukaryotic nucleosome prevents access to the genome.Convergently evolving histone isoforms,also called histone variants,form diverse families that are enriched over distinct features of plant genomes.Among the diverse families of plant histone variants,H2A.Z exclusively marks genes.Here we review recent research progress on the genome-wide distribution patterns and deposition of H2A.Z in plants as well as its association with histone modifications and roles in plant chromatin regulation.We also discuss some hypotheses that explain the different findings about the roles of H2A.Z in plants.

Epigenetic regulation of thermomorphogenesis in Arabidopsis thaliana

Temperature is a key factor in determining plant growth and development,geographical distribution,and seasonal behavior.Plants accurately sense subtle changes in ambient temperature and alter their growth and development accordingly to improve their chances of survival and successful propagation.Thermomorphogenesis encompasses a variety of morphological changes that help plants acclimate to warm environmental temperatures.Revealing the molecular mechanism of thermomorphogenesis is important for breeding thermo-tolerant crops and ensuri ng food security under global climate change.Plant adaptation to elevated ambient temperature is regulated by multiple signaling pathways and epigenetic mechanisms such as histone modifications,histone variants,and non-coding RNAs.In this review,we summarize recent advances in the mechanism of epigenetic regulation during thermo-morphogenesis with a focus on the model plant Arabidopsis thaliana and briefly discuss future pro-spects for this field.

Transcriptional Regulation of the Ambient Temperature Response by H2A.Z Nucleosomes and HSF1 Transcription Factors in Arabidopsis

Temperature influences the distribution, range, and phenology of plants. The key transcriptional activators of heat shock response in eukaryotes, the heat shock factors （HSFs）, have undergone large-scale gene amplification in plants. While HSFs are central in heat stress responses, their role in the response to ambient temperature changes is less well understood. We show here that the warm ambient temperature transcriptome is dependent upon the HSFA1 clade ofArabidopsis HSFs, which cause a rapid and dynamic eviction of H2A.Z nucleosomes at target genes. A transcriptional cascade results in the activation of multiple downstream stress-responsive transcription factors, triggering large-scale changes to the transcriptome in response to elevated temperature. H2A.Z nucleosomes are enriched at temperature-responsive genes at non-inducible temperature, and thus likely confer inducibility of gene expression and higher responsive dynamics. We propose that the antagonistic effects of H2A.Z and HSF1 provide a mechanism to activate gene expression rapidly and precisely in response to temperature, while preventing leaky transcription in the absence of an activation signal.