Assessing chromatin accessibility in maize with ATAC-seq

Maize (Zea mays) is one of the most important crop in the world. Better understanding the maize chromatin architecture points to novel approaches to improve crop yield. Here, we describe the first ATAC-seq protocol to assess the maize genome. Fresh leaf tissue was gently chopped by a blade to release intact nuclei which later were fractionated using Percoll-sucrose gradient. The isolated nuclei were treated with a transposase that fragments and tags the genome; these fragments were subjected to two rounds of PCR to generate the ATAC-seq library. In the first round of PCR, these fragments were amplified with 5 cycles and sequencing barcodes were added. A fraction of the first PCR product was subjected to qPCR to determine the optimal amplification cycle number in the second round of PCR.  The library quality can be assessed by a Bioanalyzer prior to sequencing. The distinct bands indicated good quality. After sequencing, the computational analysis of fragment size distribution may show patterns of periodicity that is a characteristic to ATAC-seq libraries. In our preliminary analysis, we found that 85% percent of the identified regions deviate from closed regions previously identified by MNase-seq, suggesting that the ATAC-seq library preparation procedure described here is effective in identifying open chromatin regions of the maize genome. We extract the maize's nuclei to apply on Maize ATAC-Seq, provide a new way to study the role of chromatin accessibility. From the Library QC data, can show a successful ATAC-Seq library characteristics. 2500 nuclei is the best numbers for do maize ATAC-Seq.