Gene regulatory network of auxin signaling

Transcriptional networks controlling hormones responses in Arabidopsis thaliana
Plants are built from numerous different types of cells, each performing specific functions to
support growth, development, survival and reproduction. Little is known how cells are
programmed and different cell types specified. The phytohormone auxin plays a critical role
in regulation of cell division and differentiation during plant development through
transcriptional regulation of specific genes. It is of fundamental relevance to determine how
transcription factor networks are set up and function to enable hormone response cascades and
subsequent physiological and developmental responses. Key regulators of auxin-mediated
gene expression are 22 ARF and 29 Aux/IAA proteins. The combinatorial action of these
factors determines the different characteristic developmental responses. Recent investigations
using microarray approaches demonstrated that not all Aux/IAA genes are regulated by auxin
and that other factors (besides auxin) participate in their regulation. Moreover, auxin
regulates not only Aux/IAA genes but also other transcriptional factors. Here we plan to
elucidate regulatory networks by applying chemical genetics using single Arabidopsis cells.
Time series analysis of the transcriptome of these cells allowed to define the topology of
regulatory networks controlling hormone action. We managed to define the topology of gene
networks acting in auxin signaling. 52 transcription factors, differentially regulated by auxin,
were found including homeobox genes and members of other families. In this project we will,
by combining expression profiling, loss-of-function experiments, chromatinimmunopreciptation (ChIP-chip) experiments, elucidate and model the regulatory network
that determines auxin responses. These networks will be extended from single cells to more
complex organs to model and simulate auxin induced programs in plant development.