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Research: Project

Transcriptional regulation at the shoot apical meristem during floral transition of Arabidopsis thaliana analyzed by transcript profiling and reverse genetics

Aimone Porri, Max Planck Institute of Plant Breeding

Flowering of Arabidopsis thaliana is tightly controlled by photoperiod (day-length). Changes in day-length are perceived in leaves where a mobile signal is generated that moves through the phloem to the shoot apical meristem (SAM). This signal causes changes in gene expression that allow the SAM to produce flowers rather than leaves. Genetic analysis demonstrated that expression of FT and its homologue TSF is activated in leaves and their proteins can move to the meristem. FT is required for the activation of genes such as SOC1 and FUL at the meristem, leading eventually to flower development (Fig 1).

Fig 1.  Arabidopsis thaliana floral initiation. Light induces expression of FT and TSF in the leaf, these proteins then move to the meristem and trigger flowering along with FD by activation of SOC1 and FUL.

Figure 1

The aims of this project are to find new genes activated in the SAM during the floral transition, to identify those genes that depend upon FT /SOC1/FUL for their expression at the apex and assess their function in flowering by reverse genetics.

Seedlings of WT, ft tsf and soc1 ful mutants are grown for 2 weeks in short days (SDs) and shifted to long days (LDs) to trigger flowering. Meristems of plants grown in SDs and LDs are being collected by Laser Capture Microdissection (LCM). Total RNA will be extracted and cDNA synthesised. The cDNA will be sequenced using the Illumina/Solexa system to obtain global gene expression profiles and to identify genes induced in the meristem during floral induction. The responses of the WT and mutant plants will be compared to relate the induced genes to the activity of FT/SOC1/FUL.

Results from sequencing will provide a certain number of genes that show altered expression levels during the floral transition. Comparing the WT dataset with the ft tsf and soc1 ful datasets will identify genes that alter their expression levels under long days independently of FT, TSF and their targets at the apex. Genes showing interesting patterns of expression will be inactivated by identifying a T-DNA insertion or using a synthetic microRNA and the effect of gene inactivation on flowering time or floral development will be assessed.

One example of a gene expressed in the meristem during flowering is Terminal Flower 1 (TFL1) which acts as a floral repressor. The study of TFL1 expression pattern by In Situ Hybridization revealed an increase of its transcript levels during floral transition under our conditions (Fig.2) and therefore it could be used as a marker gene for reproductive phase transition.

Fig 2. Expression pattern of TFL1 during floral transition by In Situ Hybridization. The hybridization was performed in shoot apical meristem of wt, soc1ful and ft-tsf plants after 2 weeks in SDs and after 2weeks in SDs +3 LDs. Yellow arrows indicate the group of cells that express TFL1

Figure 2

 

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