基金Acknowledgments The authors thank Dr Liying Du (Peking University, China) for technical help on the flow cytometric analysis. The authors also thank Dr Zhongchi Liu (University of Maryland, USA), Dr Chun-Ming Liu (Institute of Botany CAS, China), Dr Terry Matthew (University of Southampton, UK), Professor Daochun Kong (Peking University, China) and Dr Naomi Nakayama (Yale University, USA) for critical comments and valuable discussion. This work was supported by the National Natural Science Foundation of China (GN 30625002 to L-J Qu).