Alternative functions of Hd1 in repressing or promoting heading are determined by Ghd7 status under long-day conditions

Zhanyi Zhang,Yongzhong Xing,Xiangchun Zhou,Guojing Shen,Haiyang Liu,Yong Hu,Wei Hu,Touming Liu

doi:10.1038/s41598-017-05873-1

Abstract

Previous studies suggested that Hd1 promoted heading under short-day conditions (SD) and delayed heading under long-day conditions (LD). However in this study, Hd1 was demonstrated to consistently promote heading date in Zhenshan 97 (ZS97) background by upregulating Ehd1, Hd3a and RFT1 expression under both SD and LD. While the high photoperiod sensitivity of Hd1 was observed in Minghui 63 (MH63) background, with heading being suppressed in LD but promoted in SD. Comparative analysis of two sets of near isogenic lines of Hd1 in MH63 and ZS97 backgrounds indicated that the alternative functions of Hd1 in promoting or suppressing heading under LD are dependent on the previously cloned flowering repressor gene Ghd7. The interaction between proteins Ghd7 and Hd1 occurred through binding of the CCT domain of Ghd7 to the transcription-activating domain of Hd1, resulting in suppression of Ehd1 and florigen gene expression. The involvement of the transcription-activating domain of Hd1 in this protein-protein interaction probably blocked or weakened its transcriptional activity. These findings suggest that Hd1 alone essentially acts as a promoter of heading date, and the protein interaction between Ghd7 and Hd1 determines photoperiod sensitivity and integrated Hd1-mediated and Ehd1-mediated flowering pathways in rice.

Highlights

Rice (Oryza sativa L.) is a facultative short-day plant
Hd1 is photoperiod insensitivity in Zhenshan 97 (ZS97), which was not consistent with a previous report that Hd1 promotes heading in short-day conditions (SD) but delays heading in LD19
Photoperiod insensitivity of Hd1 was previously observed in Hd1 mutant that delayed heading regardless of day length as compared to its wild type[39]

Summary

Introduction

Rice (Oryza sativa L.) is a facultative short-day plant. It perceives the day length and flowers faster in short-day (SD) than in long-day (LD) conditions. Ehd[1], which encodes a B-type response regulator, is a rice-specific heading date gene functioning upstream of Hd3a for which no ortholog has been identified in Arabidopsis[20]. Several genes with pleiotropic effects on heading date, plant height, grain number and grain yield have been identified, such as Ghd[7], Ghd8/DTH8 and Ghd7.115–18 These genes delay heading date by suppressing Ehd[1] and increasing grain yield under LD. The genes of Ghd[7], Ghd8/DTH8, Ghd7.1 and OsCOL4 have been identified in the latter pathway These genes repress the transcription of Hd3a and RFT1 (Rice Flowering Locus T 1) by downregulating Ehd[1] expression independent of Hd1 in LD30. Our objectives are (1) to accurately characterize the photoperiod of Hd1; (2) to identify which gene is interacted with Hd1; and (3) to elucidate how the function of Hd1 reverses between LD and SD

Objectives

Methods

Results

Conclusion