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Research: Project

The role of the transcription factor JAGGED in early organ growth

Katharina Schiessl, John Innes Centre, Norwich

Our project aims to understand how master regulatory genes downstream of floral organ identity genes direct cell behaviour and local organ growth, ultimately, leading to very distinct species-specific organ shapes.

Following up results from previous work on the floral organ identity gene AGAMOUS (Gomez et al., 2005), this project is going to focus on one of the direct targets of AGAMOUS, the transcription factor-encoding JAGGED gene.

JAGGED has been previously described as being involved in organogenesis of lateral organs by promoting cell division, particularly, in the distal regions by Dinneny et al. (2004). Mutants of JAGGED have serrated leaves, narrow and reduced perianth and reproductive organs. By contrast, ectopic expression of JAGGED is enough to promote organ growth, as demonstrated by outgrowth of cryptic bracts, and causes extension of the blade tissue along the petioles in leaves, elongated sepals forming snake-like leafy structures. More recently, quantitative imaging experiments on floral organ primordia have suggested that JAGGED is involved in transition to and progression through S-phase of the cell cycle (Kausika and Sablowski, unpublished).

These most recent observations offer a starting point to address the question on how JAGGED interacts with regulatory genes directing local growth in vegetative as well as reproductive lateral organs. However, the mode of action and direct downstream target genes of JAGGED still remain to be discovered. Therefore, the main objective of this project is to identify genes directly responsive to JAGGED and, furthermore, to obtain sequence information on direct in vivo DNA binding sites of JAGGED.

In order to identify gene candidates that are immediate targets of JAGGED, transcription profiling will be performed by microarray analysis. In addition, chromatin immuno-precipitation (ChIP) with subsequent Illumina deep sequencing (ChIP-Seq) will be conducted in order to obtain sequence data on DNA binding sites of JAGGED. For both these approaches, experiments will be carried out in an organ-, tissue-, and developmental stage specific context.

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