SDG724 mediates H3K36me2/3 deposition at MADS50 and RFT1, and promotes flowering in rice
Changhui Sun, Jun Fang, Taolan Zhao, Bo Xu, Fantao Zhang, Linchuan Liu, Jiuyou Tang, Xiaojian Deng, Fan Chen, Qian Qian, Xiaofeng Cao, Chengcai Chu^*

Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
^*Corresponding Author：Tel: (+8610) 6480 6608; Fax: (+8610) 6480 6608; E-mail: ccchu@genetics.ac.cn

Abstract
Chromatin modifications are known to affect flowering time in the long-day (LD) plant Arabidopsis. However, the role of histone methylation in flowering time regulation of rice, a short-day (SD) plant, remains to be elucidated. We identified a late-flowering long vegetative phase 1 (lvp1) mutant in rice, and map-based cloning revealed that LVP1 encodes the SET domain group protein 724 (SDG724). Biochemical characterization showed that SDG724 is an active histone methyltransferase in vitro and contributes to a major fraction of global H3K36 methylation in vivo. Expression analyses of flowering time genes in wild-type and lvp1 mutants revealed that Ehd1, but not Hd1, are misregulated in SDG724 loss of function mutants to promote flowering under both SD and LD conditions. In addition, the lvp1 se5 double mutant flowered later than the se5 single mutant, indicating that lesions in SDG724 delay flowering time irrespective of photoperiod. ChIP assays showed that lvp1 had reduced levels of H3K36me2/3 within certain chromatin regions of Os MADS50 and RFT1. This suggests that the divergent functions of paralogs RFT1 and Hd3a, and of Os MADS50 and MADS51 are in part due to differential H3K36me2/3 deposition, which also correlates with higher expression levels of Os MADS50 and RFT1 in flowering promotion of rice.

Key Words: rice, flowering transition, histone methyltransferase, H3K36 methylation, florigen