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OsEMF2b Acts as a Regulator of Flowering Transition and Floral Organ Identity by Mediating H3K27me3 Deposition at OsLFL1 and OsMADS4 in Rice

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Abstract

Flowering transition and floral organ development influence plant propagation and crop yield. Polycomb-group (PcG) gene EMF2 restrains flowering by suppressing floral organ identity genes as an epigenetic regulator in Arabidopsis. Here, we identified that OsEMF2b, a homologue of EMF2, acted as a regulator of flowering transition and floral organ identity in rice. The OsEMF2b T-DNA insertion mutations and RNA interference transgenic plants cause late flowering, whereas OsEMF2b overexpressing lines result in early flowering. The transcript levels of genes involved in rice flowering pathway differ in wild-type plants and osemf2b mutants. The transcripts of Ehd1, Hd3a, and RFT1 decrease, whereas the expression level of OsLFL1 increases in the osemf2b mutants under short-day and long-day conditions. These results indicated that OsEMF2b functioned as the upregulator of Ehd1, Hd3a, and RFT1 and the downregulator of OsLFL1 during floral induction. Quantitative RT-PCR assay indicated that OsEMF2b regulated the transcript levels of floral homeotic A-, B-, C-, D-, and E-class genes and participated in floral organ development in rice. Chromatin immunoprecipitation analyses showed that OsEMF2b was directly associated with OsLFL1 and OsMADS4, such that the H3K27me3 was enriched on these target genes chromatin in WT but not in the OsEMF2b RNAi plants. Our results demonstrate that OsEMF2b promotes flowering through direct suppressing of the OsLFL1 expression (a suppressor of flowering) via a mechanism distinct from Arabidopsis.

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Acknowledgments

We are grateful to Prof. Chungen Hu for his helpful discussions. This research was supported by grants from the National Natural Science Foundation of China (30971551) and the Fundamental Research Funds for the Central Universities (Program No.2011QC026).

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Authors and Affiliations

  1. College of Life Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China

    Shiyong Xie, Min Chen, Rong Pei & Jialing Yao

  2. National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan, 430070, China

    Yidan Ouyang

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  1. Shiyong Xie
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Correspondence to Jialing Yao.

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Fig. S1

Phenotype of Osemf2b homozygous mutants. a The phenotypes of Wild-Type plant and osemf2b homozygous mutant at heading stage under SD. b The phenotypes of Wild-Type plant and oSEMf2b homozygous mutant at heading stage under LD. c-e The phenotypes of spikelet of osemf2b homozygous mutant. WT, Wild-Type plants; Hom, osemf2b homozygous mutant. Bar 1 mm (GIF 174 kb)

High Resolution Image (TIFF 3730 kb)

Fig. S2

Observations of the inflorescence development of Wild-Type plants and osemf2b homozygous mutants confirmed the later flowering of osemf2b homozygous mutants. a The internodes of Wild-Type plants were more elongated and the young panicles in the main culms were more obvious at 55-57 days of cultivation compared with that of osemf2b homozygous mutants. The floral meristems were enlarged in the last inflorescence. b Floral transition of Wild-Type plants completed at 72 ~ 74d, a small number of osemf2b homozygous mutants began to enter reproductive stage. c osemf2b homozygous mutants from b are enlarged. WT, Wild-Type plants; Hom, osemf2b homozygous mutants. Bar 0.25 cm (GIF 24 kb)

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Fig. S3

OsEMF2b gene structure and its mutant identification. a Gene structure of OsEMF2b and T-DNA insertion site. Arrows indicate the three primers used for genotyping test. b The genotype identification result of OsEMF2b at heading stage. c Days to flowering of Wild-Type plants, osemf2b heterozygous mutants and osemf2b homozygous mutants in b. d Transcript level of Wild-Type plants, osemf2b heterozygous mutants and osemf2b homozygous mutants at heading stage. WT, Wild-Type plants; Het, osemf2b heterozygous mutants; Hom, osemf2b homozygous mutants (GIF 71 kb)

High Resolution Image (TIFF 874 kb)

Fig. S4

Relative expression level (a) and corresponding flowering time (b) of Wild-Type plants and complementation plants at heading stage in T 0 progenies. WT, Wild-Type plants; Com, Complementation plants. The blue arrow indicates negative transgenic plants; The black arrow indicates positive transgenic plants which are not restored the flowering phenotype and have similar expression level with negative transgenic plants; The red arrow indicates the three highest expression level plants. The day which T 0 transgenic plants were put into rooting medium was recorded as Day 0 (GIF 204 kb)

High Resolution Image (TIFF 7678 kb)

Fig. S5

Relative expression level (a) and corresponding flowering time (b) of Wild-Type plants and complementation plants at heading stage in T 2 progenies. WT, Wild-Type plants; Com, Complementation plants. The blue arrow indicates negative transgenic plants (GIF 183 kb)

High Resolution Image (TIFF 7729 kb)

Fig. S6

Relative expression level (a) and corresponding flowering time (b) of Wild-Type plants and OsEMF2b over-expressing transgenic plants at heading stage in T 0 progenies. WT, Wild-Type plants; OX, OsEMF2b over-expressing transgenic plants. The blue arrow indicates negative transgenic plants; The black arrow indicates positive transgenic plants which have not significant phenotype and have similar expression level with WT; The red arrow indicates the three highest expression level plants. The day which T 0 transgenic plants were put into rooting medium was recorded as Day 0 (GIF 215 kb)

High Resolution Image (TIFF 8264 kb)

Fig. S7

Relative expression level (a) and corresponding flowering time (b) of Wild-Type plants and OsEMF2b RNA interference plants at heading stage in T 0 progenies. WT, Wild-Type plants; RNAi, OsEMF2b RNA interference plants. The blue arrow indicates negative transgenic plants; The black arrow indicates positive transgenic plants which have not significant phenotype and have similar expression level with WT; The red arrow indicates the three lowest expression level plants. The day which T 0 transgenic plants were put into rooting medium was recorded as Day 0 (GIF 234 kb)

High Resolution Image (TIFF 9592 kb)

Fig. S8

Relative expression level (a) and corresponding flowering time (b) of Wild-Type plants, OsEMF2b over-expressing transgenic plants and OsEMF2b RNA interference plants at heading stage in T 2 progenies. WT, Wild-Type plants; OX, OsEMF2b over-expressing transgenic plants; RNAi, OsEMF2b RNA interference plants. The blue arrow indicates negative transgenic plants (GIF 212 kb)

High Resolution Image (TIFF 8591 kb)

Fig. S9

Diurnal expression patterns of OsEMF2b, OsLFL1, Hd3a, Ehd1, RFT1, OsMADS50, Hd1, RID1, Ghd7, OsGI, OsMADS51, and OsMADS14 in Wild-Type (filled circles) and osemf2b homozygous mutants (open circles) under LDs by quantitative RT-PCR analysis. The open and filled bars at the bottom represent the light and dark periods, respectively. WT, Wild-Type plants; Hom, osemf2b homozygous mutants (GIF 52 kb)

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Table S1

Primers used for the study (GIF 94 kb)

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Table S2

Developmental stages of the SAM in Wide-Type and osemf2b homozygous. WT, Wild-Type; Hom, osemf2b homozygous (GIF 25 kb)

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Table S3

The numbers of floral organ in Wild-Type, OsEMF2b RNA interference, osemf2b heterozygous and osemf2b homozygous; WT, Wild-Type; RNAi, OsEMF2b RNA interference; Het, osemf2b heterozygous; Hom, osemf2b homozygous (GIF 22 kb)

High Resolution Image (TIFF 1383 kb)

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Xie, S., Chen, M., Pei, R. et al. OsEMF2b Acts as a Regulator of Flowering Transition and Floral Organ Identity by Mediating H3K27me3 Deposition at OsLFL1 and OsMADS4 in Rice. Plant Mol Biol Rep 33, 121–132 (2015). https://doi.org/10.1007/s11105-014-0733-1

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