RBS1, an RNA Binding Protein, Interacts with SPIN1 and Is Involved in Flowering Time Control in Rice

Yuhui Cai,Zejian Guo,Miguel E Vega-Sánchez,Guo-Liang Wang,Chan Ho Park,Maria Bellizzi,Keqiang Wu

doi:10.1371/journal.pone.0087258

Abstract

The rice U-box/ARM E3 ubiquitin ligase SPL11 negatively regulates programmed cell death (PCD) and disease resistance, and controls flowering time through interacting with the novel RNA/DNA binding KH domain protein SPIN1. Overexpression of Spin1 causes late flowering in transgenic rice under short-day (SD) and long-day (LD) conditions. In this study, we characterized the function of the RNA-binding and SPIN1-interacting 1 (RBS1) protein in flowering time regulation. Rbs1was identified in a yeast-two-hybrid screen using the full-length Spin1 cDNA as a bait and encodes an RNA binding protein with three RNA recognition motifs. The protein binds RNA in vitro and interacts with SPIN1 in the nucleus. Rbs1 overexpression causes delayed flowering under SD and LD conditions in rice. Expression analyses of flowering marker genes show that Rbs1 overexpression represses the expression of Hd3a under SD and LD conditions. Rbs1 is upregulated in both Spin1 overexpression plants and in the spl11 mutant. Interestingly, Spin1 expression is increased but Spl11 expression is repressed in the Rbs1 overexpression plants. Western blot analysis revealed that the SPIN1 protein level is increased in the Rbs1 overexpression plants and that the RBS1 protein level is also up-regulated in the Spin1 overexpression plants. These results suggest that RBS1 is a new negative regulator of flowering time that itself is positively regulated by SPIN1 but negatively regulated by SPL11 in rice.

Highlights

IntroductionIn Arabidopsis, a long day (LD) plant, extensive genetic analyses have identified four flowering pathways: photoperiod, autonomous, vernalization, and gibberellin induced pathways, as well as a series of signaling molecules [1,2,3,4,5]
Flowering time is controlled by endogenous and environmental signals
We identified RNA-binding and SPIN1-interacting 1 (RBS1) as a novel RNA binding protein of the heterogeneous nuclear ribonucleoproteins (hnRNP)-R type in rice and showed that it interacts with SPIN1 in both yeast and rice protoplasts

Summary

Introduction

In Arabidopsis, a long day (LD) plant, extensive genetic analyses have identified four flowering pathways: photoperiod, autonomous, vernalization, and gibberellin induced pathways, as well as a series of signaling molecules [1,2,3,4,5]. The early heading date 1 (Ehd1) protein positively regulates the expression of Hd3a, influencing the flowering time in rice independent of Hd1. This pathway only exists in rice as there is no Ehd ortholog in Arabidopsis [11]. It has been shown that the rice florigen protein Hd3a interacts with 143-3 proteins in the apical cells of shoots, yielding a complex that translocates to the nucleus and binds to the OsFD1 transcription factor to regulate flowering time [14]

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Conclusion