Transcription factor interaction with COMPASS-like complex regulates histone H3K4 trimethylation for specific gene expression in plants.

Accumulation of unfolded or misfolded proteins causes endoplasmic reticulum (ER) stress, which activates a set of ER membrane-associated transcription factors for protein homeostasis regulation. Previous genome-wide chromatin immunoprecipitation analysis shows a strong correlation between histone H3K4 trimethylation (H3K4me3) and active gene expression. However, how the histone modification complex is specifically and timely recruited to the active promoters remains unknown. Using ER stress responsive gene expression as a model system, we demonstrate that sequence-specific transcription factors interact with COMPASS-like components and affect H3K4me3 formation at specific target sites in Arabidopsis. Gene profiling analysis reveals that membrane-associated basic leucine zipper (bZIP) transcription factors bZIP28 and bZIP60 regulate most of the ER stress responsive genes. Loss-of-functions of bZIP28 and bZIP60 impair the occupancy of H3K4me3 on promoter regions of ER stress responsive genes. Further, in vitro pull-down assays and in vivo bimolecular fluorescence complementation (BiFC) experiments show that bZIP28 and bZIP60 interact with Ash2 and WDR5a, both of which are core COMPASS-like components. Knockdown expression of either Ash2 or WDR5a decreased the expression of several ER stress responsive genes. The COMPASS-like complex is known to interact with histone methyltransferase to facilitate preinitiation complex (PIC) assembly and generate H3K4me3 during transcription elongation. Thus, our data shows that the ER stress stimulus causes the formation of PIC and deposition of H3K4me3 mark at specific promoters through the interaction between transcription factor and COMPASS-like components.

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