Homodimerization of Ehd1 Is Required to Induce Flowering in Rice.

Lae-Hyeon Cho,Richa Pasriga,Gynheung An,Jinmi Yoon

doi:10.1104/pp.15.01723

Lae-Hyeon Cho, Richa Pasriga + Show 2 more

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https://doi.org/10.1104/pp.15.01723

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Abstract

In plants, flowering time is elaborately controlled by various environment factors. Ultimately, florigens such as FLOWERING LOCUS T (FT) or FT-like molecules induce flowering. In rice (Oryza sativa), Early heading date 1 (Ehd1) is a major inducer of florigen gene expression. Although Ehd1 is highly homologous to the type-B response regulator (RR) family in the cytokinin signaling pathway, its precise molecular mechanism is not well understood. In this study, we showed that the C-terminal portion of the protein containing the GARP DNA-binding (G) domain can promote flowering when overexpressed. We also observed that the N-terminal portion of Ehd1, carrying the receiver (R) domain, delays flowering by inhibiting endogenous Ehd1 activity. Ehd1 protein forms a homomer via a 16-amino acid region in the inter domain between R and G. From the site-directed mutagenesis analyses, we demonstrated that phosphorylation of the Asp-63 residue within the R domain induces the homomerization of Ehd1, which is crucial for Ehd1 activity. A type-A RR, OsRR1, physically interacts with Ehd1 to form a heterodimer. In addition, OsRR1-overexpressing plants show a late-flowering phenotype. Based on these observations, we conclude that OsRR1 inhibits Ehd1 activity by binding to form an inactive complex.

Highlights

In plants, flowering time is elaborately controlled by various environment factors
Heading date 1 (Ehd1) is a unique gene that induces the expression of Heading date 3a (Hd3a) and Rice Flowering locus T1 (RFT1), two florigens in rice (Doi et al, 2004; Zhao et al, 2015)
We show that OsRR1, a type-A RR, suppresses flowering by interacting with Early heading date 1 (Ehd1)

Summary

Introduction

In plants, flowering time is elaborately controlled by various environment factors. florigens such as FLOWERING LOCUS T (FT) or FT-like molecules induce flowering. Type-A RRs are the negative components that turn off this signal by forming feedback regulatory loops (Hwang and Sheen, 2001; Hwang et al, 2002, 2012; To et al, 2004) This type of RR is thought to bind and inhibit type-B RRs, which are transcription activators (Kim, 2008). Cytokinin signaling is a sequential phosphorelay similar to bacterial two-component response systems Both RR types are activated by phosphorylation of the middle Asp (D) in the conserved AspAsp-Lys (D-D-K) motif within the R domain (West and Stock, 2001; Hwang et al, 2002). The subcellular localization of RR proteins is not affected by phosphorylation (Sakai et al, 2000; Tsai et al, 2012)

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