Auxin Signalling Pathway

Auxin initiate complex growth and development processes in plants through its signalling pathway. The mechanism of action of this hormone facilitate the rapid or spontaneous switching between transcriptional repression and gene activation via the auxin-dependent degradation of transcriptional repressor.

The signalling pathway consists of small number of core proteins or protein components which are represented by large gene family. This core proteins belongs to 3 protein family.

. At the molecular level, auxin induces gene expression through direct physical interaction with the TIR1-like F box proteins, which in turn remove the Aux/IAA family of transcriptional repressors, A growing body of evidence indicates that many plant pathogens can either produce auxin themselves or manipulate host auxin biosynthesis to interfere with the host’s normal developmental processes.
In response, plants probably evolved mechanisms to repress auxin signaling during infection as a defense strategy. Plants over accumulating the defense signal molecule salicylic acid (SA) frequently display morphological phenotypes that are reminiscent of auxin-deficient or auxin-insensitive mutants, indicating that SA might interfere with auxin responses.
By using the Affymetrix ATH1 GeneChip for Arabidopsis thaliana, we performed a comprehensive study of the effects of SA on auxin signaling .
We found that SA causes global repression of auxin-related genes, including the TIR1 receptor gene, resulting in stabilization of the Aux/IAA repressor proteins and inhibition of auxin responses.
We demonstrate that this inhibitory effect on auxin signaling is a part of the SA-mediated disease-resistance mechanism.Signalling pathway for auxin

F-box Transport Inhibitor Response 1/ Auxin Signalling F-box protein (TIR1/AFB)Auxin/ Indole-3-Acetic Acid (AUX/IAA)transcriptional repressorAuxin Response For (ARF) transcription factors.

The hormone auxin facilitate the interaction of TIR/AFB and AUX/IAA. Hence leading to the release of ARF repression. Gene expression associated with ARF activation have been implicated in diverse processes in land plants, Including embryogenesis, establishment of polarity and tropic responses.

´┐╝At low concentrations of auxin levels, AUX/IAA transcriptional repressor interact with ARF and repress their activity. When TIR1/AFB proteins bind to AUX/IAA transcriptional repressor which mediates the subsequent poly ubiquitylation and subsequent proteasomal degradation. Rapid induction of auxin responsive genes including a us AUX/IAA, GH3 negative feedback loops. AUX/IAAtranscriptional repressor interact with proteins in the signallin pathway through three different domains leucine repeat EAR motif within domain 1Internal domain II which contains a GWP-core degron motifC- terminal region

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