Constitutive expression of OsDof4, encoding a C2-C2 zinc finger transcription factor, confesses its distinct flowering effects under long- and short-day photoperiods in rice (Oryza sativa L.)

Qi Wu,Hua Yuan,Xianfeng Zhao,Lihuang Zhu,Shigui Li,Qi Xie,Xue Liu,Xiaobing Li,Dayong Li,Dedong Yin

doi:10.1186/s12870-017-1109-0

Abstract

BackgroundDof (DNA binding with one finger) proteins, a class of plant-specific transcription factors which contain a conserved C2-C2-type zinc finger domain, are involved in many fundamental processes. In the Arabidopsis photoperiod response pathway, CDF (CYCLING DOF FACTOR) proteins have a primary role as acting via transcriptional repression of the direct FLOWERING LOCUS T (FT) activator CONSTANS (CO). Our previous study indicated that one of CDF homologs, OsDOf12, was involved in photoperiodic flowering. However, the functional characterization of other rice CDF like genes is still in progress. Here, we characterized the function of OsDof4 in rice.ResultsPhylogenic analysis indicated that OsDof4 is closely clustered into the same subgroup with CDFs and OsDof12. The subcellular localization experiment and transcriptional activity assay suggested that OsDof4 may function as a transcription factor. The diurnal expression pattern indicated that OsDof4 was regulated by endogenous circadian clock. Overexpression of OsDof4 led to earlier flowering under natural long-day field conditions (NLDs) and late flowering under natural short-day field conditions (NSDs), respectively. We compared the expression level of key floral genes in vector line and OsDof4-ox lines grown under long-day conditions (LDs) and short-day conditions (SDs). Real-time q-PCR results demonstrated that under LDs, Hd3a, RFT1 and Ehd1 were up-regulated whereas under SDs they were down-regulated. Hd1 was down-regulated at dusk period independent of photoperiods.ConclusionsTaken these results together, we may speculate that the abnormal flowering responses in OsDof4-ox plants under LDs and SDs might be mediated by Ehd1 and Hd1.

Highlights

Dof (DNA binding with one finger) proteins, a class of plant-specific transcription factors which contain a conserved C2-C2-type zinc finger domain, are involved in many fundamental processes
The phylogenic tree indicated that OsDof2, OsDof4, OsDof5, OsDof6, OsDof12, OsDof23 and OsDof26 are closely clustered with CYCLING DOF FACTOR (CDF) (Fig. 1a), we named them OsCDFs (Oryza sativa CDFs)
We found that pGAL4DBD-OsDof4 exerted obviously enhanced transcriptional activation ability compared with pGAL4DBD (Fig. 3b), implying that OsDof4 is capable of activating transcription, which further confirmed that OsDof4 encodes a rice transcription factor

Summary

Introduction

Dof (DNA binding with one finger) proteins, a class of plant-specific transcription factors which contain a conserved C2-C2-type zinc finger domain, are involved in many fundamental processes. In the Arabidopsis photoperiod response pathway, CDF (CYCLING DOF FACTOR) proteins have a primary role as acting via transcriptional repression of the direct FLOWERING LOCUS T (FT) activator CONSTANS (CO). Extensive studies have revealed Arabidopsis thaliana, a facultative long-day plant (LDP), and rice (Oryza sativa), a facultative short-day plant (SDP), share a conserved photoperiodic flowering signaling cascade: GIGANTEA (GI)-CONSTANS (CO)-FLOWERING LOCUS T (FT) [6, 7]. In Arabidopsis, under inductive long-day conditions (LDs) GI and FLAVIN-BINDING, KELCH REPEAT, F-Box 1 (FKF1) form more stable complexes to increase the CO expression level, a direct activator of FT, by post-transcriptionally degrading CYCLING DOF FACTOR1 (CDF1) which is a CO transcriptional repressor, promoting flowering [8, 9]. When switched from inductive SDs to non-inductive LDs, Hd1 converts into a repressor of Hd3a by the modification of red-light photoreceptor Phytochrome B (PhyB) [14]

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