An auxin regulated positive feedback loop integrates Rho modulated cell polarity with pattern formation.

In plants, polar transport of the hormone auxin between cells connects cell polarity and pattern formation and is thus required for plant development. The direction of auxin transport is determined by polar localization of PIN auxin efflux transporters. The dynamic polar localization of PIN proteins depends on constitutive endocytic recycling to and from the plasma membrane. However, it was not well understood how PIN polarization is connected to regulators of cell polarity. In a paper that was published in the January issue of PLoS Biology, 2010 we described the involvement of the ROP GTPase associated scaffold Interactor of Constitutive active ROP 1 (ICR1) in recruitment of PIN proteins to polar domains in the plasma membrane. icr1 mutant plants and embryos have severe developmental aberrations that are caused by abnormal auxin distribution. ICR1 functions at or close to the plasma membrane where it is required for exocytosis. ICR1 transcription is quickly induced by auxin but is post-transcriptionally repressed at the site of stable auxin maximum in embryos and roots. Thus, ICR1 integrates auxin-regulated transcription with ROP modulated cell polarity.