2.2　DNA extraction and genome sequencing

Total DNA was extracted from the stroma of O.sinensis by a modified CTAB method as previously described(Kang et al.，2011).The integrity，quality and concentration of total DNA were analyzed by agarose gel electrophoresis，NanoDrop 1000 spectrophotometer and Qubit fluorometer.DNA was randomly sheared to fragments with an average size of 20 kb by using g-TUBE.Sheared DNA was then DNA damage repaired and end repaired.SMRTbell templates were obtained by ligating the blunt hairpin adapters to the ends of the repaired fragments，followed by the addition of exonuclease to remove failed ligation products.Before annealing the sequencing primer and binding polymerase to SMRTbell templates，the quality of library was assessed by an Agilent 2100 Bioanalyzer High Sensitivity Kit.Eight SMRT cells were sequenced using P6-C4 reagents on a PacBio RSⅡsequencing platform(Pacific Biosciences，Nextomics Biosciences Co.，Ltd.，Wuhan).(https://www.daowen.com)