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doi: 10.1242/10.1242/dev.00113

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early in short days 4, a mutation in Arabidopsis that causes early flowering and reduces the mRNA abundance of the floral repressor FLC

Paul H. Reeves1,2,*, Giovanni Murtas1,*, Sudhansu Dash1 and George Coupland1,2,{dagger}

1 John Innes Centre, Colney Lane, Norwich NR4 7UH, UK
2 Max Planck Institute for Plant Breeding, Carl Von Linne Weg 10, D-50829 Cologne, Germany



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  		Fig. 1. Phenotype of the esd4 mutant. (A) A wild-type plant (left) and an esd4 mutant (right) grown under long days. Both plants are 5 weeks old. (B) A wild-type plant (left) and an esd4 mutant (right) grown under short days. Both are 6 weeks old. (C) An esd4 mutant grown under long days. The arrows indicate siliques that have developed in unexpected positions. (D) The section of the stem of esd4 mutants shown in C at higher magnification. (E) A comparison of silique shape in wild-type (left) and esd4 (right) plants. (F-H) The apex of 4-week-old plants: (F) wild-type; (G) esd4 mutant; (H) esd4 mutant showing the pistil-like structure (arrow) that terminates the shoot. (I,J) Scanning electron micrographs of the apex of the shoot 4-week-old wild-type (I) and esd4 mutant (J) plants grown under long days. The scale bars are 300 µm. (K) Schematic diagram illustrating the structure of wild-type and esd4 plants. The arrows represent indeterminate shoots, the circles flowers, and rosette and cauline leaves are shown as ovals. (L) The frequency with which various abnormalities were recorded at the node containing the last cauline leaf or the first flower. CL, cauline leaf; S, solitary flower; I, inflorescence. Percentages illustrate the proportion of plants that showed each abnormality. Fewer than 1% of wild-type plants showed any of these abnormalities.

 


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  		Fig. 2. Histogram comparing the number of juvenile, adult and cauline leaves in wild-type (Ler) and esd4 mutants. Plants were grown under both long days (LD) and short days (SD).

 


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  		Fig. 3. Photographs illustrating the phenotypes of double mutants carrying esd4 grown under long days. In each panel an esd4 mutant is shown on the left and the following double mutants on the right. (A) esd4 co-2; (B) esd4 ft-1; (C) esd4 fwa-1; (D) esd4 fca-1; (E) esd4 fve-1; (F) esd4 gai. All plants are 4 weeks old.

 


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  		Fig. 4. Photographs illustrating the phenotypes of double mutants carrying esd4 grown under short days. In A-E an esd4 mutant is shown on the left and the following double mutants on the right. (A) esd4 co-2; (B) esd4 ft-1; (C) esd4 fwa-1; (D) esd4 fca-1; (E) esd4 fve-1. (F) An esd4 ga1-3 double mutant. All plants are 6 weeks old.

 


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  		Fig. 5. Analysis of the of the expression of the flowering time genes FLC, FT, SOC1 and CO in wild-type and esd4 mutant plants. (A) Northern blot comparing FLC mRNA levels in 7-day-old Ler, esd4, fca-1, esd4 fca-1, fve-1, and esd4 fve-1 plants. The panel on the right is a longer exposure of the Ler and esd4 samples. (B) Northern blot comparing FT mRNA levels in 7-day-old Ler, esd4, fca-1 and esd4 fca-1 plants. The graph shows the mean level of FT gene expression relative to the UBQ10 control. In all graphs, black triangles represent Ler, black squares esd4, white triangles fca-1 and white squares esd4 fca-1; error bars indicate the standard error of the mean. (C) Northern blot comparing SOC1 mRNA levels in 7-day-old Ler, esd4, fca-1 and esd4 fca-1 plants. The graph shows the mean level of SOC1 gene expression relative to the UBQ10 control. Error bars indicate the standard error of the mean. (D) RT-PCR analysis of CO expression in 7-day-old wild-type and esd4 plants. The graph shows the level of CO gene expression relative to the UBQ10 control. Error bars indicate the standard error of the mean. (A-D) All experiments were performed three times using RNA from independently grown plant material.

 


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  		Fig. 6. Models for the role of ESD4 in the regulation of flowering time. (A) ESD4 acts within the autonomous pathway to repress flowering and ESD4 activity is repressed by the activity of FCA/FVE. (B) ESD4 acts to repress flowering, in part by promoting high levels of the floral repressor FLC. Genes repressed by FLC include FT and SOC1, but it is likely that other genes (X) are also regulated by FLC. Both the autonomous and vernalization pathways act to regulate FLC mRNA levels (Sheldon et al., 1999Go; Sheldon et al., 2000Go; Michaels and Amasino, 1999; Michaels and Amasino, 2001Go), and ESD4 may interact with genes in these pathways. Genetic and molecular evidence suggests that ESD4 is likely to repress flowering independently of FLC (represented by dotted line), as does the promotion of flowering by vernalization (Michaels and Amasino, 2001Go). The genes regulated in an FLC-independent manner by ESD4 are represented by Y and probably include FT and SOC1, as the level of expression of FT and SOC1 is similar in wild type and esd4 fca-1 mutants, despite higher levels of FLC mRNA in esd4 fca-1 plants. Mutations in the long day and gibberellin pathways delay the flowering of esd4 mutants by affecting the activity of genes that are common targets of several floral promotion pathways.

 

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