1. School of Biological Sciences, Nanyang Technological University , Singapore 637551 , Singapore
2. National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University , Wuhan 430070 , China
3. Hubei Hongshan Laboratory , Wuhan 430070 , China
4. Department of Plant and Soil Sciences, Kentucky Tobacco Research and Development Center, University of Kentucky , Lexington, KY 40546 , USA