design: Sequencing libraries were generated using NEBNext DNA Library Prep Kit. The genomic DNA was randomly fragmented to a size of 350bp by shearing; DNA fragments were end polished, A-tailed, and ligated with the NEBNext adapter for Illumina sequencing, and further PCR enriched by P5 and indexed P7 oligos. The PCR products were purified (AMPure XP system, United States), followed by analysis for size distribution. Qualified libraries were sequenced on an Illumina platform.