Figure 9.

Model Depicting Sequential Changes in Chromatin Modifications over the phas Promoter during Potentiation and Activation.

In the repressed state during vegetative growth, the promoter is repressed by nucleosomes bearing dimethylated H4-K20. Pv-ALF–mediated potentiation (Step 1) is predicted to recruit RLT2, a component of ISWI chromatin-remodeling complex that also contains the CHR11-like SWI2/SNF2 ATPase. During this stage, ordered histone modifications occur by demethylation of histone H3-K4, acetylation of H3-K14 and H4-K5, and histone methylation (Ng et al., 2006). As illustrated in Step 1, this results in remodeling of the chromatin architecture over the TATA region of the phas promoter but does not lead to transcriptional activation in the absence of ABA. During the ABA-dependent activation illustrated in Step 2, Pv-ALF induces AIL5, which activates the expression of the phas promoter.