1. Warnell School of Forestry and Natural Resources, University of Georgia , Athens, GA 30602, USA
2. Department of Genetics, University of Georgia , Athens, GA 30602, USA
3. Department of Plant Biology , Athens, GA 30602, USA
4. Department of Bioscience and Biotechnology, Beijing Forestry University , Beijing 100083, China
5. Department of Biotechnology, School of Life Science and Engineering, Southwest University of Science and Technology , Mianyang 621010, Sichuan, China