Acknowledgments:This study was supported by the Fundamental Research Funds for Central Universities (2572017PZ02), the Strategic Priority Research Program of the Chinese Academy of Sciences (grant No. XDB 26000000, the Shenzhen Municipal Government of China (grant No. JCYJ20170817145132389) and the Guangdong Provincial Key Laboratory of Genome Read and Write (grant No. 2017B030301011). We thank the Guangdong Provincial Academician Workstation of BGI Synthetic Genomics, BGI-Shenzhen, Guangdong, China. Finally, we are thankful to the China National GeneBank for producing the sequencing data. We thank Xiaohui Liu for giving suggestions on data analysis, Chenhui Liu and Dan Xiong for helping plot figures.