The plant hormone auxin is a key factor in the control of cell fate at the shoot apical meristem. Auxin is transported in a polar fashion throughout tissues and a large body of evidence suggests that this transport generates local differences in auxin concentrations. However, very little is known on how the auxin signal is perceived in the meristem and how such local differences could be translated into changes in cell fate and cell behavior.

At the cellular level, the members of the Aux/IAA and ARF transcription factor families have been identified as the key effectors in auxin signal transduction. There are 29 Aux/IAA genes, which encode mostly short-lived repressors of auxin-inducible genes. The 23 ARF proteins can be either activators (Q-rich ARFs) or repressors of transcription. Aux/IAA and ARF proteins are able to form homo- and heterodimers both within and between the families. Given the complexity of the auxin transduction pathway, we have developed a systems biology approach combining molecular and computer-based experiments to obtain a global view of the mechanisms controlling signal transduction of auxin in a complex tissue, the meristem.

We are using an in situ hybridization approach to elucidate the spatial expression pattern of all Aux/IAAs and ARFs in the shoot apical meristem. This first level of analysis allows us to build a detailed expression map of these genes in the meristem.

To complement the in situ hybridization data, we are using a high-throughput yeast-2-hybrid approach to study all possible interactions between the Aux/IAAs and ARFs. This interaction matrix, together with the expression map of the genes, allows us to obtain the local auxin transduction network in the different zones of the meristem.

Finally, we have initiated in parallel a modeling approach using differential equations to analyze the behavior of the Aux/IAA-ARF network.

I will present and discuss our latest results on the project.