OsELF3-1, an Ortholog of Arabidopsis EARLY FLOWERING 3, Regulates Rice Circadian Rhythm and Photoperiodic Flowering

Junming Zhao,Shiguang Wang,Xi Huang,Shigui Li,Ling Zhu,Weilan Chen,Xing Wang Deng,Anping Du,Xinhao Ouyang,David Edward Somers

doi:10.1371/journal.pone.0043705

Abstract

Arabidopsis thaliana EARLY FLOWERING 3 (ELF3) as a zeitnehmer (time taker) is responsible for generation of circadian rhythm and regulation of photoperiodic flowering. There are two orthologs (OsELF3-1 and OsELF3-2) of ELF3 in rice (Oryza sativa), but their roles have not yet been fully identified. Here, we performed a functional characterization of OsELF3-1 and revealed it plays a more predominant role than OsELF3-2 in rice heading. Our results suggest OsELF3-1 can affect rice circadian systems via positive regulation of OsLHY expression and negative regulation of OsPRR1, OsPRR37, OsPRR73 and OsPRR95 expression. In addition, OsELF3-1 is involved in blue light signaling by activating EARLY HEADING DATE 1 (Ehd1) expression to promote rice flowering under short-day (SD) conditions. Moreover, OsELF3-1 suppresses a flowering repressor GRAIN NUMBER, PLANT HEIGHT AND HEADING DATE 7 (Ghd7) to indirectly accelerate flowering under long-day (LD) conditions. Taken together, our results indicate OsELF3-1 is essential for circadian regulation and photoperiodic flowering in rice.

Highlights

Flowering, referred to as heading date in rice (Oryza sativa), is an important agronomical trait for rice to adapt to specific cropping environments
Under short-day (SD) conditions, OsGI is an activator of Heading date 1 (Hd1), the rice ortholog of Arabidopsis CO [10]; Hd1 promotes flowering by activating Heading date 3a (Hd3a), the rice ortholog of FLOWERING LOCUS T (FT) [11,12,13]
OsELF3-1 and OsELF3-2 respectively share 35% and 30% identity with EARLY FLOWERING 3 (ELF3) in their amino acid sequences (Fig. S1). To investigate whether these two genes are involved in rice flowering, we examined the heading dates of oself3-1 and oself3-2 mutant in the experimental field of Sichuan province (30u679) and Hainan province (18u159) in China

Summary

Introduction

Flowering, referred to as heading date in rice (Oryza sativa), is an important agronomical trait for rice to adapt to specific cropping environments. Determined by photoreceptors, circadian clock systems and floral integrator genes, photoperiodic regulation is a key means in controlling plant flowering [1,2,3]. A sophisticated signaling network of photoperiodic flowering has been revealed initially based on the identification of key functional genes in Arabidopsis thaliana [4]. In the evolutionarily conserved GIGANTEA(GI)-CONSTANS(CO)-FLOWERING LOCUS T (FT) signaling pathways [3], clock-associated protein GI positively regulates CO expression under long-day conditions (LD) [5]. Under short-day (SD) conditions, OsGI is an activator of Heading date 1 (Hd1), the rice ortholog of Arabidopsis CO [10]; Hd1 promotes flowering by activating Heading date 3a (Hd3a), the rice ortholog of FT [11,12,13]. RICE FLOWERING LOCUS T 1 (RFT1/FT-L3) is extensively homologous to Hd3a, and these two homologs function redundantly in the flowering [14,15]

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Conclusion