For all living organisms, the survival and reproductive success strongly depends on their ability to perceive and integrate both external and internal signals. Due to their sessile life style and in contrast to most animals, plants have developed an extensive flexibility allowing them to modify their development in order to cope with fast changing environments. Such flexibility has been made possible by a set of morphological adjustments, which regulate the growth of organs, such as leaves or roots.

Robert Stephanie 1150Developmental changes are often mediated by cell elongation, which is a very complex process in plants due to the presence of the cell wall, located outside the cell membrane. Cell wall provides support and protection to the plant cell and thus has to be fairly rigid. However, this compartment also needs to be flexible to allow cell elongation and general growth.The plant primary cell wall is composed of cellulose microfibrils (the main component), hemicelluloses, pectins and proteins (Figure 1).The interactions between these components, modulated by different enzymatic activities such as hydrolysis, transglycosylation and disruption of hydrogen bonds,are believed to increase elasticity, thus permitting cell elongation. Furthermore, synthesis and deposition of new material is subsequently required to sustain growth.As a key regulator of plant development, IAA modulates cell elongation via the establishment of an auxin gradient. One of the auxin properties is to stimulate cell elongation by induc- ing wall loosening (Ray et al., 1972).This effect is enhanced in presence of gibberellins, highlighting the importance of phy- tohormones in the adjustment of the cell wall. Many aspects of the regulation of cell elongation/plant growth remain elusive and by using Arabidopsis thaliana, for which a wide range of biologic and molecular tools have been developed, there are undoubtedly opportunities to increase our comprehension of plant development processes.

robert s picture 1 robert s picture 2
Endomembrane trafficking pathways and cell wall biosynthesis. After their biosynthesis, cell wall components can go through different pathways (1. Delivery of soluble cargo and integral protein to plasma membrane, 2. Recycling of PM material (endocytosis/exocytosis), 3. Degradation of proteins through MVBs). Cellulose synthases (CESAs, light blue rosette) move along the actins filaments (in green) to reach the plasma membrane. Cortical microtubules (in dark-green) that lie beneath the membrane act rather like rails along which the CESA moves. The resulting cellulose aggregates to form fibres. The noncellulosic components are secreted to the cell surface and form a matrix assembled around the cellulose microfibrils. Picture adapted from a figure kindly given by Delphine Gendre (SLU, UPSC). Endoplasmic Reticulum (ER), Trans-Golgi- Network (TGN), Multivesicular Body (MVB). Example of a chemical genomics strategy used to study the endomembrane system. An automated image-based screen was developed to find inhibitors of pollen germination in vitro, which depends on vesicle transport. Several of the selected chemicals caused mis-localization of plasma membrane markers.

However, dissecting rapid processes involved in plant de- velopment such as trafficking mechanisms that target cellular components to their final destination or phytohormone signaling is challenging for classical genetic experiments due to the diversity of the pathways and gene function redundancy. Chemical genetics is the use of small molecules to modify or disrupt the function of specific proteins (Figure 2, Robert et al., 2009).This is analogous to genetic mutations with the benefit that chemical biology can ideally bypass many of the difficulties inherent in classical genetics such as gene redundancy or lethal- ity in loss of function mutants. Given the enormous structural versity among small molecules and the flexibility offered by the large concentration range and/or application time, chemical biology may effectively address biological questions.

In our group, we aim to dissect and separate, at a cellular level, the different signaling pathways involved in plant growth, using the cutting-edge approach of chemical genomics combined with classical genetics and analytical approaches.The goal of our projects is therefore to identify novel signaling pathways to enhance our basic knowledge about important components of plant growth regulation.

Publication list

  1. Polar expedition: mechanisms for protein polar localization
    Curr Opin Plant Biology 2020, January 23 Online
  2. Chemical screening pipeline for identification of specific plant autophagy modulators
    Plant Physiol. 2019, 181(3):855-866
  3. A role for the auxin precursor anthranilic acid in root gravitropism via regulation of PIN-FORMED protein polarity and relocalisation in Arabidopsis
    NEW PHYTOLOGIST 2019, 223(3):1420-1432
  4. Mechanical Asymmetry of the Cell Wall Predicts Changes in Pavement Cell Geometry
    Developmental Cell 2019, 50 (1), 9-10
  5. FORCE-ing the shape
    Current Opinion in Plant Biology 2019, 52:1–6
  6. A role for the auxin precursor anthranilic acid in root gravitropism via regulation of PIN-FORMED protein polarity and relocalization in Arabidopsis
    New Phytol. 2019 Apr 30 [Epub ahead of print]
  7. Selective auxin agonists induce specific AUX/IAA protein degradation to modulate plant development
    Proc Natl Acad Sci U S A. 2019, 116(13):6463-6472
  8. The Inhibitor Endosidin 4 Targets SEC7 Domain-Type ARF GTPase Exchange Factors and Interferes with Subcellular Trafficking in Eukaryotes
    PLANT CELL 2018, 30(10):2553-2572
  9. New fluorescently labeled auxins exhibit promising anti-auxin activity
    N Biotechnol. 2018, 48:45-52
  10. The Role of Auxin in Cell Wall Expansion
    Int. J. Mol. Sci. 2018, 19(4), 951
  11. Vacuole Integrity Maintained by DUF300 Proteins Is Required for Brassinosteroid Signaling Regulation
    Mol Plant. 2017, 11(4):553-567
  12. Auxin signaling: a big question to be addressed by small molecules
    Journal of Experimental Botany 2018, 69(2):313-328
  13. Mechanochemical Polarization of Contiguous Cell Walls Shapes Plant Pavement Cells
    Developmental Cell 2017, 43(3); 290–304.e4
  14. Regulating plant physiology with organic electronics
    2017, 114(18):4597-4602
  15. Auxin 2016: a burst of auxin in the warm south of China
    Development 2017 144: 533-540
  16. 2,4-D and IAA Amino Acid Conjugates Show Distinct Metabolism in Arabidopsis
    PLoS One. 2016 Jul 19;11(7):e0159269 eCollection 2016
  17. Mitochondrial uncouplers inhibit clathrin-mediated endocytosis largely through cytoplasmic acidification
    Nature Communications 7, Article number: 11710
  18. Extra- and intracellular distribution of cytokinins in the leaves of monocots and dicots
    N Biotechnol. 2016, 33(5):735-742
  19. Small molecules unravel complex interplay between auxin biology and endomembrane trafficking
    J Exp Bot. 2015, 66(16):4971-4982
  20. Osmotic stress modulates the balance between exocytosis and clathrin-mediated endocytosis in Arabidopsis thaliana
    Mol Plant. 2015 Mar 17. pii: S1674-2052(15)00175-6 [Epub ahead of print]
  21. An early secretory pathway mediated by GNOM-LIKE 1 and GNOM is essential for basal polarity establishment in Arabidopsis thaliana
    Proc Natl Acad Sci U S A. 2015, 112(7):E806-15
  22. Live Cell Imaging of FM4-64, a Tool for Tracing the Endocytic Pathways in Arabidopsis Root Cells
    Methods Mol Biol. 2015;1242:93-103
  23. Unraveling plant hormone signaling through the use of small molecules
    Front. Plant Sci June 2014; 5:373
  24. The cellulase KORRIGAN is part of the Cellulose Synthase Complex
    Plant Physiol. 2014 Jun 19, pp.114.241216
  25. Trafficking modulator TENin1 inhibits endocytosis, causes endomembrane protein accumulation at the pre-vacuolar compartment and impairs gravitropic response in Arabidopsis thaliana.
    Biochem J. 2014; 460:177-185
  26. Using a reverse genetics approach to investigate small-molecule activity
    Methods Mol Biol. 2014;1056:51-62
  27. Auxin biology revealed by small molecules
    Physiol Plant. 2014, 151(1):25-42
  28. The use of chemical biology to study plant cellular processes – subcellular trafficking
    Plant Chemical Biology 22 NOV 2013
  29. ABCG9, ABCG11 and ABCG14 ABC transporters are required for vascular development in Arabidopsis
    The Plant Journal, 2013; 76(5):811-824
  30. ECHIDNA-mediated post-Golgi trafficking of auxin carriers for differential cell elongation
    Proc Natl Acad Sci U S A. 2013 , 110(40):16259-16264
  31. Defining the selectivity of processes along the auxin response chain: a study using auxin analogues
    New Phytol. 2013, 200(4):1034-1048
  32. ROOT ULTRAVIOLET B-SENSITIVE1/WEAK AUXIN RESPONSE3 Is Essential for Polar Auxin Transport in Arabidopsis
    PLANT PHYSIOLOGY, 2013; 162(2):965-976
  33. The Caspase-Related Protease Separase (EXTRA SPINDLE POLES) Regulates Cell Polarity and Cytokinesis in Arabidopsis
    Plant Cell 2013; 25(6):2171-2186
  34. Cell Polarity and Patterning by PIN Trafficking through Early Endosomal Compartments in Arabidopsis thaliana
    PLOS genetics May 30 2013
  35. Auxin: simply complicated
    Journal of Experimental Botany, Online: May 13, 2013
  36. ROOT UVB SENSITIVE 1/WEAK AUXIN RESPONSE 3 Is Essential for Polar Auxin Transport in Arabidopsis
    Plant Physiology April 2013 Published online before print April 2013
  37. Baster P, Robert S, Kleine-Vehn J, Vanneste S, Kania U, Grunewald W, De Rybel B, Beeckman T, Friml J
    SCF(TIR1/AFB)-auxin signalling regulates PIN vacuolar trafficking and auxin fluxes during root gravitropism
    EMBO J. 2012 Dec 4
  38. Chen X, Naramoto S, Robert S, Tejos R, Löfke C, Lin D, Yang Z, Friml J
    ABP1 and ROP6 GTPase Signaling Regulate Clathrin-Mediated Endocytosis in Arabidopsis Roots
    Curr Biol. 2012, 22(14):1326-32
  39. Recycling, clustering, and endocytosis jointly maintain PIN auxin carrier polarity at the plasma membrane
    Molecular Systems Biology 7:540
  40. Clusters of bioactive compounds target dynamic endomembrane networks in vivo
    PNAS 2011, 108(43):17850-17855
  41. Barberon M, Zelazny E, Robert S, Conéjéro G, Curie C, Friml J, Vert G
    Monoubiquitin-dependent endocytosis of the IRON-REGULATED TRANSPORTER 1 (IRT1) transporter controls iron uptake in plants
    Proceedings of the National Academy of Sciences of the United State of America: 2011 108:E450-E458
  42. Kitakura S. Vanneste S, Robert S, Löfke C, Teichmann T, Tanaka H, Friml J
    Clathrin mediates endocytosis and polar distribution of PIN auxin transporters in Arabidopsis
    The Plant Cell: 2011, 23:1920-1931
  43. Arabidopsis ROOT UVB SENSITIVE2/WEAK AUXIN RESPONSE1 is required for polar auxin transport
    The Plant Cell: 2010 22:1749-1761
  44. ABP1 mediates auxin inhibition of clathrin-dependent endocytosis in Arabidopsis
    Cell: 2010 143:111-121
  45. Robert S, Raikhel NV, Hicks GR
    Powerful partners: Arabidopsisi and chemical genomics
    In: The Arabidopsis Book. Rockville, MD: American Society of Plant Biologists; 2009. p 1-16.
  46. Drakakaki G, Robert S., Raikhel NV, Hicks GR
    Chemical dissection of endosomal pathways
    Plant Signaling and Behavior: 2009 4:1-6
  47. Naramoto S, Kleine-Vehn J, Robert S, Fujimoto M, Dainobu T, Paciorek T, Ueda T, Nakano A, Van Montagu MCE, Fukuda H, Friml J
    ADP-ribosylation factor machinery mediates endocytosis in plant cells
    Proceedings of the National Academy of Sciences of the United States of America: 2010 107:21890-21895
  48. Robert S, Chary N, Drakakaki G, Yang Z, Raikhel N, Hicks G
    Endosidin1 defines a compartment involved in endocytosis of the brassinosteroid receptor BRI1 and the auxin transporters PIN2 and AUX1
    Proceedings of the National Academy of Sciences of the United States of America: 2008 105:8464-8469
  49. Isolation of intact vacuoles from Arabidopsis rosette leaf-derived protoplasts
    Nature Protocols: 2007 2:259-262
  50. Divergent functions of VTI12 and VTI11 in trafficking to storage and lytic vacuoles in Arabidopsis
    Proceedings of the National Academy of Sciences of the United States of America: 2007 104:3645-3650
  51. Drakakaki G, Zabotina O, Delgado I, Robert S, Keegstra K, Raikhel N
    Arabidopsis RGP1 and RGP2 are essential for pollen development
    Plant Physiology: 2006 142:1480-1492
  52. Robert S, Bichet A, Grandjean O, Kierskowski D, Satiat-Jeunmaitre B, Pelletier S, Hauser M-T, Höfte H, Vernhettes S
    An Arabidopsis endo-1,4-β-D-glucanase involved in cellulose synthesis undergoes regulated cellular cycling
    The Plant Cell: 2005 17:3378-3389
  53. Robert S, Mouille G, Höfte H
    The mechanism and regulation of cellulose synthesis in primary wall: lessons from primary cell wall mutants
    Cellulose: 2004 11:351-364