1. State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, Guangdong 510642, China
2. College of Horticulture, South China Agricultural University, Guangzhou, Guangdong 510642, China
3. Donald Danforth Plant Science Center, St. Louis, Missouri 63132
4. University of Missouri-Columbia, Division of Plant Sciences, Columbia, Missouri 65211