A grant was assigned incorrectly to the third author. The grant was issued to the second author, Yong-ming Yao. The correct funding statement is: "This study was supported, in part, by grants from the National Natural Science Foundation of China (http://www.nsfc.gov.cn/Portal0/default124.htm)(grant no. 81000847 to Q-yL; 81071545 to Yong Ming Yao), and the National Basic Research Program of China (http://www.973.gov.cn/)(grant no. 2005CB522602 to Yong Ming Yao). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript."
Footnotes
Competing Interests: No competing interests declared.