FDP a novel regulator of primordia fate

When plants grow they produce clumps of cells, called primordia, at their growing tips. All the above ground parts of the plant are ultimately derived from these primordia. Most plants grow vegetatively first, making stems and leaves, before initiating flowering. In the laboratory we study the development of a small plant called Arabidopsis. Although it is just a weed, Arabidopsis has many advantages for scientists to work on it, and we believe that what we learn about Arabidopsis will be relevant to many other plants. When arabidopsis grows, the first 15 or so primordia that are initiated are vegetative, that is they make leaves. After this time, if the conditions are right, the plant will make flowers instead of leaves. This developmental decision to make leaves or flowers is very important, and controlled by many factors. We want to understand more clearly how the switch from making leaves to making flowers works in plants. We have identified a mutant, fdp-1, where the switch is damaged, and as a result the plants make flowers much earlier than they should. Indeed, in the fdp-1 mutant, many genes are expressed where and when they shouldn't be. This gene therefore represents an exciting tool to understand in molecular terms aspects of how plants control the switch from making leaves to flowers in the primodia. We shall use a combination of different approaches to understand this problem. We wish to discover what other genes are affected by FDP. We will do this using microarrays. We also wish to discover the mechanism of FDP signaling, is it direct, or does it act through a repressor? Finally, we wish to do genetic screens to identify other genes involved.

A critical question in biology concerns how developmental switches work to control growth and morphogenesis. We have identified an essential component necessary for floral repression, FDP. FDP encodes a bZIP transcription factor, and loss of function alleles display early and terminal flowers and show massive misregulation of floral meristem identity genes such as AGAMOUS and APETALA1. During vegetative growth FDP is expressed in the sites of the future axillary meristems and in the centre of the apical meristem. Following the floral transition, FDP expression becomes restricted to the centre of the shoot apical meristem. FDP interacts by 2-hybrid and genetically with the well characterised floral repressor TERMINAL FLOWER 1 (TFL1).We will characterise the nature of the interaction of FDP and TFL1 in vivo. To understand the global effects of fdp-1 on development, we will identify its transcriptional targets. Putative cis-regulatory elements will be identified and analysed in vivo. Protein domain analysis and cell based assays will be used to verify if FDP acts as a direct transcriptional repressor. A forward genetic screen based on the strong fdp-1 phenotype will be used to identify additional players in the FDP pathway.