DNA extraction and sequencing
For Illumina sequencing, the phenol/chloroform extraction protocol was used to extract DNA from 2g of young leaves. An Illumina sequencing library for an insertion length of 250 bp was prepared using the TruSeq Nano DNA LT Library Preparation Kit (Illumina Inc., USA). DNA purity and size range were evaluated with Agilent Bioanalyzer 2100 (Agilent Technologies, Santa Clara, CA). An Illumina sequencing library (PE) with an insertion length of 300-350 bp was constructed and sequenced using the Illumina HiSeq 2000 platform.
The DNA extracted from the young leaves was also used for the PacBio sequencing library construction. According to the manufacturer’s protocol (Pacific Biosciences, USA), 10 μg of Chinese flowering cabbage genomic DNA were used for 30-kb template library preparation using the BluePippin Size Selection system (Sage Science, USA). The library was sequenced on the PacBio SEQUEL II platform.
The PacBio platform was used to generate long genomic reads for the construction of a reference genome for the Chinese flowering cabbage. After removing adaptor sequences, more than 113Gb of subreads were obtained with 219 times sequence coverage. The sequencing data were used for the following genome assembly operations.