1. Key Laboratory of Plant Cell Engineering and Germplasm Innovation; Ministry of Education; School of Life Sciences; Shandong University; Jinan Shandong 250100 China
2. State Key Lab of Agrobiotechnology; Institute of Plant Molecular Biology and Agrobiotechnology; School of Life Science; The Chinese University of Hong Kong; Shatin New Territories Hong Kong China
3. DuPont Pioneer AgBiotech Research; Johnston Iowa 50131-1004 USA
4. Horticultural Sciences Department; University of Florida; Gainesville FL 32611 USA