We thank Mr. X Yan in Wuhan Institutes of Biotechnology for technical help. This work was financially supported by Science and Technology Supporting Program of Hubei Province, China (2014BBB007), Key Project of Science and Technology Research Program of the Education Department of Hubei Province (no. D20131703), the Key Project of Chinese Ministry of Education (no. 212118). Dr. JK Yang is an incumbent of the Chutian Scholar Program position.