Nature Communications 8: Article number: 14864; DOI: 10.1038/ncomms14864 (2017)); Published: March 28 2017; Updated: April 25 2017
The original version of this Article contained a typographical error in the spelling of the author Beifang Niu, which was incorrectly given as Beifung Niu. This has now been corrected in both the PDF and HTML versions of the Article.