Measuring Arabidopsis chromatin accessibility using DNase I-polymerase chain reaction and DNase I-chip assays.

DNA accessibility is an important layer of regulation of DNA-dependent processes. Methods that measure DNA accessibility at local and genome-wide scales have facilitated a rapid increase in the knowledge of chromatin architecture in animal and yeast systems. In contrast, much less is known about chromatin organization in plants. We developed a robust DNase I-polymerase chain reaction (PCR) protocol for the model plant Arabidopsis (Arabidopsis thaliana). DNA accessibility is probed by digesting nuclei with a gradient of DNase I followed by locus-specific PCR. The reduction in PCR product formation along the gradient of increasing DNase I concentrations is used to determine the accessibility of the chromatin DNA. We explain a strategy to calculate the decay constant of such signal reduction as a function of increasing DNase I concentration. This allows describing DNA accessibility using a single variable: the decay constant. We also used the protocol together with AGRONOMICS1 DNA tiling microarrays to establish genome-wide DNase I sensitivity landscapes.