1. Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops; College of Horticulture; China Agricultural University; Beijing 100193 China
2. Plant Biology Section; School of Integrative Plant Science; Cornell University; Ithaca NY 14853 USA
3. Department of Agronomy; Purdue University; West Lafayette IN 47907 USA
4. Boyce Thompson Institute; Cornell University; Ithaca NY 14853 USA