Molecular-genetic approaches to study the role FT in photoperiodic flowering of Arabidopsis

In many plant species, the transition from vegetative growth to flowering is controlled by day length. Plants are able to detect changes in day length through a regulatory pathway that acts in the leaves. Two of the most relevant genes involved in this mechanism are CONSTANS (CO) and FLOWERING LOCUS T (FT). In Arabidopsis, under long day conditions (LD), CO activates the transcription of FT. Subsequently, FT protein moves through the phloem to the shoot apical meristem (SAM) where, together with FD, it triggers changes in the expression of genes such as SUPPRESOR OF OVEREXPRESSION OF CONSTANS (SOC1). Both FT and SOC1 activate floral meristem identity genes such as APETALA1 (AP1) and LEAFY (LFY). These genes in turn lead to cell reprogramming and the formation of floral organs. Recent studies have demonstrated that TWIN SISTER OF FT (TSF), a close homologue of FT, is also regulated by CO and participates in the photoperiodic flowering pathway redundantly with FT. Despite the importance of FT/TSF in flowering control their function in leaves and the SAM is poorly understood as is their relationship to other signals required for floral induction. In order to address some of these questions, we are performing a “three-way-strategy” implementing different genetic and genomics approaches. To identify novel flowering components related to the FT pathway an EMS mutant collection has been generated from the ft tsf double mutant, which is insensitive to day length and very late flowering under long days. In the M2 of this population we are screening for early and late flowering mutants that may reveal pathways acting in parallel with FT/TSF or negative regulators of the FT activated pathway in the meristem. Additionally, we are generating EMS mutant populations from GAS1::FT in tsf ft plants which are early flowering. Here we hope to identify positively acting components downstream of FT. Secondly, to investigate the global effects of FT on gene expression in leaves, we are making use of the GeneChip® Arabidopsis Tiling 1.0R Array (Affymetrix, Inc). Taking advantage of this technology, we are studying which genes are specifically affected by FT and/or TSF by comparing Col-0 (wild type) with ft tsf and GAS1::FT in tsf ft genotypes. Finally, we are studying the genetic events that are taking place in the SAM during floral induction. In previous studies carried out in our group several differentially expressed genes were identified in the SAM after the shift from SD to LD conditions by exploiting laser dissection microscopy and Solexa sequencing. Currently, we are testing many candidate genes by in situ hybridizations on meristems of Col-0, ft tsf and other genotypes. With this strategy, we expect to be able to draw a network of distinct components affecting flowering in the meristem and to relate these to known components such as FT and SOC1. Furthermore, several of these genes show spatial patterns of expression in the meristem that had not previously been described, revealing additional layers of regulation in the meristem