The research in our laboratories was supported by National Natural Science Foundation of China (No. 31372319 and 31402084), the Hubei Provincial Key Project for Scientific and Technical Innovation (2014ABA022), Hubei Provincial Research and Development Program (No. 2010BB023), Natural Science Foundation of Hubei Province (No. 2013CFA097, 2013CFB325, 2012FFB04805, 2011CDA131), Scientific Research Program of Hubei Provincial Department of Education (D20141701), the Hubei Hundred Talent Program, Agriculture and Food Research Initiative Competitive Grants of (2014-67015-21770) of the USDA National Institute of Food and Agriculture, and Texas AgriLife Research (H-82000). All these funding agencies had no role in the design, analysis or writing of this study. The authors declare that they have no conflict of interest.