Jirí Friml
Auxin, Polarity, Patterning
VIB Department of Plant Systems Biology, UGent 

PhD: Univ. of Cologne, Cologne, Germany, '00 PhD: Masaryk Univ., Brno, Czech Republic, '02 Postdoc: Univ. of Tübingen, Tübingen, Germany, '01-'02 Group leader: Univ. of Tübingen, Tübingen, Germany, '02-'07 Full Professor: Univ. of Göttingen, Göttingen, Germany, '07 VIB Group leader since 2007

e-mail phone +32 9 331 39 13 ADDRESS

Current team members
Group leader: Jirí Friml
Postdoctoral scientists: Hélène Boisivon, Hirokazu Tanaka, Jurgen Kleine-Vehn, Niloufer Irani, Saeko Kitakura, Satoshi Naramoto, Sibylle Hirsch, Steffen Vanneste, Stéphanie Robert, Wim Grunewald, Xu Chen, Yun-Long Du, Zhaojun Ding
Ph.D. Students: Elena Feraru, Elke Barbez, Jing Zhang, Krzysztof Wabnik, Lukasz Langowski, Marta Zwiewka, Pawel Baster, Ricardo Tejos, Tomasz Nodzynski, Urszula Kania
Support personnel: Ioan-Mugurel Feraru, Ruth De Groodt

Keywords
auxin - auxin transport - cell polarity - vesicle trafficking - endocytosis - tropisms - patterning

Science

Plant development is characterised by a pronounced adaptability to different environmental conditions. Extensive post-embryonic development, involving the activity of permanent stem cell populations (meristems), de novo organ formation and changes in growth direction, provides plants with an exceptional flexibility in terms of growth and survival. Differential distribution (gradients) of the plant signalling molecule auxin underlies many of these developmental events. These gradients are established and maintained by a directional, intercellular auxin transport called polar auxin transport. Polar auxin transport provides positional and directional information for many aspects of plant development.
Classical models postulate that polar auxin transport requires the activity of auxin influx and efflux carriers. Molecular genetic studies in the model plant Arabidopsis thaliana have identified AUX1/LAX and PIN gene families coding for components of influx and efflux carriers, respectively. Studies in cultured plant, mammalian and yeast cells show that PINs mediate auxin efflux from cells. The PIN gene family in Arabidopsis consists of eight members, and orthologues have been found in most other plant species. Genetic studies have revealed the roles of the different PIN proteins in the establishment of auxin gradients mediating multiple developmental processes including apical organogenesis and phyllotaxis, gravitropic and phototropic growth, root meristem patterning, vascular tissue development and embryonic axis formation.
The key feature of polar auxin transport – its controlled directionality - was postulated to result from the asymmetric, subcellular localisation of the efflux carriers. Remarkably, as predicted, PIN proteins display an asymmetric localisation within auxin transport competent cells and determine the direction of auxin flow. The decision on PIN polar targeting depends on their phosphorylation regulated by PINOID kinase and PP2AA phosphatase. As cellular levels (and thus the activity of PINOID) are dependent on auxin itself, this provides a possible feed-back regulation between auxin and PIN polarity.
Polar targeting of PIN proteins is related to their continuous subcellular movement between endosomes and the plasma membrane. PIN internalization occurs by the clathrin-dependent endocytosis mechanism and its recycling back to the plasma membrane requires ARF GEF regulators of vesicle trafficking. The constitutive cycling of auxin transport components provides an entry point for internal and external signals, which in this manner can rapidly modulate PIN polarity. Dynamic changes of PIN polarity in response to environmental and developmental signals have been observed to divert auxin flow during gravitropic response, embryogenesis, postembryonic organogenesis and tissue regeneration. In addition, auxin itself can influence the subcellular distribution of plasma membrane proteins including PINs by inhibiting their endocytosis and thus regulate activity of its efflux.
These data show that PIN proteins are key components of an intricate auxin distribution network that mediates local auxin gradients in multiple developmental processes.
It also represents a unique model system to study the functional link between basic cellular processes, such as endocytosis or cell polarity establishment, and their developmental outcome at the level of the multicellular plant organism.

Press releases
See also press release (16/01/2009): Combating infection of crops by nematodes is soon to improve - based on a publication in PloS Pathogens (Grunewald et al., PloS Pathogens, 2009) 

See also press release (27/10/2008): Scientists unveil mechanism for ‘up and down’ in plants - based on a publication in Nature (Dhonukse et al., Nature, 2008).

Vanneste S, Friml J
Auxin: a trigger for change in plant development
CELL 136, 1005-16, 2009



Mravec J, Skupa P, Bailly A, Hoyerová K, Krecek P, Bielach A, Petrásek J, Zhang J, Gaykova V, Stierhof Y, Dobrev P, Schwarzerová K, Rolcik J, Seifertová D, Luschnig C, Benková E, Zazimalová E, Geisler M, Friml J
Subcellular homeostasis of phytohormone auxin is mediated by the ER-localized PIN5 transporter
NATURE 459, 1136-40, 2009



Dhonukshe P, Tanaka H, Goh T, Ebine K, Mahonen A, Prasad K, Blilou I, Geldner N, Xu J, Uemura T, Chory J, Ueda T, Nakano A, Scheres B, Friml J
Generation of cell polarity in plants links endocytosis, auxin distribution and cell fate decisions
NATURE 456, 962-6, 2008



Michniewicz M, Zago M, Abas L, Weijers D, Schweighofer A, Meskiene I, Heisler M, Ohno C, Zhang J, Huang F, Schwab R, Weigel D, Meyerowitz E, Luschnig C, Offringa R, Friml J
Antagonistic Regulation of PIN Phosphorylation by PP2A and PINOID Directs Auxin Flux
CELL 130, 1044-56, 2007



Wisniewska J, Xu J, Seifertová D, Brewer P, Ruzicka K, Blilou I, Rouquie D, Benková E, Scheres B, Friml J
Polar PIN localization directs auxin flow in plants
SCIENCE 312, 883, 2006

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