Figure 12

Hypothetical model for histone chaperone function during development and stress response in plants. Schematic diagram shows a simplified model for function of histone chaperones at developmentally-regulated and stress-regulated genetic loci in plants. Histone chaperones (marked as HC) with the coordinated action of other factors (shown as shapes with question marks) including those involved in chromatin remodelling, DNA demethylation, histone methylation, and histone acetylation by HATs (histone acetyl transferases) may promote transcriptional competence in the direction of the downward blue arrow. In this direction, histone chaperones primarily aid the transient eviction of histones from the chromatin template leading to the assembly of pre-initiation complex (PIC) followed by transcription. On the other hand, in the reverse direction (shown by upward red arrow) histone chaperone may function to deposit histones onto the DNA template. The resulting enhanced nucleosome occupancy, which may also require the functioning of histone deacetylases (HDACs), some histone methyl transferases and the DNA methylation machinery apart from histone chaperones, leads to transcriptional repression. Precisely which factors cooperate with histone chaperones resulting in either of the two contrasting outcomes (transcriptional competence or repression), during stress response and developmental programming and reprogramming in plants, remains to be worked out and hence are shown as shapes with question marks. Broken lines represent the classic nucleosome structure in continuation.