Title: Darwin had it right: phototropic auxin relocalization is conserved between dicots and monocots
Lecturer: Dr Angus Murphy, Department of Horticulture, Purdue University, USA
Place: KB3B3, KBC

Abstract: Plants depend on sunlight for photosynthesis and adjust their growth to optimize light capture. Phototropism, the reorientation of growth toward light, is one of the most important of these adaptive processes. Originally identified in grass coleoptiles by Charles and Francis Darwin, phototropism is initiated by light perceived at the shoot tip to generate a diffusible signal that influences differential elongation in the tissues below. Subsequent studies have shown that phototropism arises from increased growth on the shaded side of the stem, owing to an accumulation of the phytohormone auxin.
Research from the past two decades has identified and characterized the PHOTOTROPIN (PHOT) blue light receptors as the primary receptors that modulate phototropic curvatures in the model plant Arabidopsis. Downstream signalling effectors are assumed to act on auxin transport proteins from the PIN, AUX1/LAX, and ABCB families to control directional auxin movement.
However, somewhat surprisingly, it is still not clear how these receptor mechanisms actually control auxin movement in the shoot apex and what the exact path of auxin movement is in. We have established a system in Arabidopsis to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis and hook opening. Using this system, we have shown that auxin redistribution to epidermal sites of action occurs at the hypocotyl apex in dicots as is the case in monocots, not out of the vascular cylinder in the hypocotyl elongation zone as has been assumed for the past decade.
Within this region, we identified the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as the first substrate target for the photoreceptor kinase PHOTOTROPIN1(PHOT1). In vivo and in vitro analyses showed that phosphorylation of ABCB19 by PHOT1 inhibits ABCB19 efflux activity and increases auxin levels in the cotyledonary node to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN3. These results demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperms, but also demonstrated that no single or viable double or triple mutant in known auxin transporters bends phototropically. As no new non-bending mutant has been identified in the many screens for phototropism mutants over the past decade, either a missing component of the process that mediates auxin redirection is essential for viability, or the full complement of transporters that function in lateral auxin redistribution has not been discovered. In any case, the widely held perception that the mechanism underlying lateral redistribution of auxin in phototropism has been resolved is not supported by substantive data.

Title: Distribution and regulation of Auxin in Arabidopsis root cells
Sara V. Petersson, Department of Forest Genetics and Plant Physiology, SLU, Umeå
Place: Sal Björken at SLU in Umeå

Opponent: Dr Angus Murphy, Department of Horticulture, Purdue University, USA

Title: Analysis of somatic mutations in three populations of Scots pine (Pinus sylvestris)
by Master student Jani Basha Mohammad
Place: KBF30, UPSC

Title: Cold sensing and signaling in Arabidopsis thaliana
Paulina Stachula, Department of Plant Physiology, Umeå University
Place: KB3A9 "Lilla hörsalen", KBC

Title: Expanding the JAZ protein interaction network
Lecturer: Laurens Pauwel, VIB Department of Plant Systems Biology, Ghent University, Belgium
Place: KB3A9 "Lilla hörsalen", KBC

Title: Structural insights into the mechanism of G protein coupled receptor activation
Speaker: Brian Kobilka, Molecular and Cellular Physiology and Medicine, Beckman Center, Stanford University, CA, U.S.A.
Place: KB3A9 "Lilla hörsalen", KBC

Research Overview
Research in my lab is directed at understanding the structural basis for the functional properties of G protein coupled receptors (GPCRs),which constitute the largest family of membrane proteins in the human genome. GPCRs conduct the majority of transmembrane responses to hormones and neurotransmitters, and mediate the senses of sight, smell and taste. The beta 2 adrenoceptor (beta2AR) is a prototypical Family A GPCR that mediates physiologic responses to adrenaline and noradrenaline. It regulates the activity of several distinctsignaling pathways through both G protein dependent and G protein independent mechanisms. Like many GPCRs that respond to hormones and neurotransmitters, the beta2AR exhibits modest basal activity in the absence of an agonist. This activity can be modulated by a spectrum of synthetic ligands ranging from inverse agonists, which suppress basal activity, to full agonists. We have obtainedthree-dimensional structures of the beta2AR in inactive and active conformations; and we have used fluorescence spectroscopy and NMR spectroscopy to study the dynamic properties of the receptor, and to map ligand-specificconformational changes. I will discuss what we these studies have taught usabout the structural basis of beta2AR function.

The Company ConfometRX
Structure-based drug discovery for G Protein Coupled Receptors

G protein coupled receptors (GPCRs) represent the largest family of membrane proteins in the human genome, and the largest class of targets for drug discovery. Clinical indications for GPCRs include cardiovascular, pulmonary, metabolic and psychiatric disorders, as well as inflammation, cancer and HIV infection.

ConfometRx is developing a platform of structure-based drug discovery technologies to facilitate lead identification and lead optimization for G protein coupled receptors.

This platform includes:
• biophysical technologies for characterizing ligand-induced structural changes in GPCRs
• the generation of GPCR-specific, functional antibodies for target validation, therapeutics and protein crystallography
• the production of pure, functional GPCRs for high-resolution structure determination by crystallographythe economical and efficient labeling of GPCRs with 13C and 15N for NMR spectroscopy studies to characterize receptor-ligand interactions

Publications: Xao, X.J., Vélez Ruiz, G., Whorton, M.R., Rasmussen, S.G.F., DeVree, B.T., Deupi, X.,Sunahara, R.K., and Kobilka, B.K.,The effect of ligand efficacy on the formation and stability of a GPCR-G protein complex. Proc Natl Acad Sci U S A, 2009. 106(23): p. 9501-9506. Fung, J.J., Deupi, X., Pardo, L., Yao, X.J., Velez-Ruiz, G.A., DeVree, B.,Sunahara, R.K., and Kobilka, B.K.,Ligand regulated oligomerization of beta2-adrenoceptors in a model lipid bilayer.EMBO Journal, 2009. 28(21): p. 3315-28.

Rosenbaum, D.M., Rasmussen, S.G., Kobilka, B.K.The structure and function of G-protein-coupled receptors.Nature, 2009. 459(7245): 356-363.

Bokoch, M.P., Zou, Y., Rasmussen, S.G.F., Liu, C.W., Nygaard, R.,Rosenbaum, D.M., Fung, J.J., Choi, H.J., Thian, F.S., Kobilka, T.S., Puglisi, J.D.,Weis, W.I., Pardo, L., Prosser, R.S., Mueller, L., Kobilka, B.K. Ligand-specific regulation of the extracellular surface of a G proteincoupled receptor. Nature, 2010. 463:p.108-112.

Title: Determinants of sugar-specific gene expression in plants
Sabine Kunz, Department of Plant Physiology, Umeå University
Place: KB3A9 "Lilla hörsalen", KBC

Title: Probing molecular mechanisms regulating trafficking of auxin influx carriers
Lecturer: Ranjan Swarup, University of Nottingham, United Kingdom
Place: KB3A9 "Lilla hörsalen", KBC