Symposia on Plant (Protein) Phosphorylation

From September 14 to 16, 2011 the 12th symposium on Plant Protein Phosphorylation was held in Tübingen, Germany. The topic is as broad as the name suggests and covers all aspects of this important means of protein modification in plants. I have had the pleasure of attending the 2007 and the 2011 symposia. The interesting concept behind these meetings is to hear about the same biochemical mechanism operative in a multitude of experimental systems. The meetings are quite informal and present an excellent mix ranging from technology to biochemical experience and novel findings and tools. The two-and-a-half-day program was divided into five double sessions: biotic interactions, hormone signaling, abiotic interactions, Mitogen Activated Protein Kinase (MAPK), and Ca++ pathways and phosphoproteomics. It was hosted by the Zentrum für Molekularbiologie der Pflanzen (ZMBP) and the organizing committee chaired by Klaus Harter. In the biotic interactions session the role of phosphorylation in PathogenTriggered Immunity (PTI) was the central topic. Several speakers discussed differential phosphorylation events after turning on the PTI pathways. The first presentation was by Yuelin Zhang (Beijing) who discussed recent work on identifying targets of the MAPK pathway using a suppressor screen. To what extent cross talk between growth and PTI pathways exists at the level of the receptors was discussed by Cyril Zipfel (Norwich). Important points raised were whether the dynamics of receptor activation as observed in brassinosteroid receptors are directly applicable to the non-Arginine Aspartic Acid (RD) type of kinases that seem to feature in most PTI pathways. A very intriguing report was made by Iris Jarsch (Munich), suggesting a role for remorins to sequester receptors in small membrane micro domains. Looking in the very first events of membrane receptor activation, it appears that changes in heteromeric state of Flagellin Sensing 2 (FLS2) and BRI1 Associated Kinase (BAK1) can be seen a mere few seconds after ligand application (Birgit Schulze, Basel). Speed was also the topic of a presentation from the host (Klaus Harter, Tübingen), showing evidence for direct activation of plasma membrane adenosine triphosphatases (PM ATPases) by the BRI1 receptor. Down-regulation by endocytosis of the FLS2 receptor, negative control elements such as phosphatases appear to play more and more important roles in controlling receptor activity and sensitivity (Antje Heese, Columbia; Roda Niebergall, Norwich) while genes have been identified that modulate the calcium signature of the PTI response (Justin Lee, Halle). A much-explored theme in the signaling session was to isolate receptor-interacting proteins by direct pull downs or yeast interaction screens. This was used in approaches by Sorina Popescu (Ithaca) investigating reticulon-like proteins that regulate trafficking and activity of FLS2 and Sacco de Vries (Wageningen) looking at the interaction properties of members of the Somatic Embryogenesis Receptor-like Kinase (SERK) family of non-ligand binding coreceptors that includes BAK1(SERK3). Other work dealt with control of cellulose synthase by phosphorylation (Martine Gonneau, Versailles), subcellular relocalization of Pin-formed (PIN) proteins through phosphorylation by PINOID kinases (Eike Rademacher, Leiden) and several talks on the direct control of abscisic acid (ABA) signaling by Protein Phosphatase 2C (PP2C) enzymes (Erwin Grill, München; Rainer Hedrich, Würzburg) including interesting kinases that lack the conserved lysine in the catalytic domain called With No K (WNK)s; Esther Görlich, Heidelberg). Using an alternative approach by comparing phosphorylation patterns in the presence or absence of a specific inhibitor of the salicylic acid (SA) response-mediating Casein Kinase 2 (CK2), an SA-induced phosphorylated p23 protein was identified that may act in a Heat Shock Protein (HSP) 90 complex (Stefano d’Allessandro, Padua). Clearly, molecular approaches using phospho-site mutants are generally applied to unravel functional relevance of the proteins under investigation. The next session was devoted to abiotic signaling and started with Jay Thelen (Columbia) introducing a number of nice generally applicable tools to discover phosphorylation sites (MUSite) and Kinase Clients including the novel peptide/mass spectrometry-based Kinase Client assay (KiC assay). He also provided many examples of the genome-wide data sets available in the Plant Protein Phosphorylation Database at Columbia. Response to Reactive Oxygen Species involves socalled Cysteine-rich Receptor-like Kinases (RLKs) that may be the direct sensors of ozone. Intriguingly, a small peptide derived from a protein called Grim Reaper (GRI) induces cell death and may function in the ROS pathway (Jaakko Kangasjärvi, Helsinki). Claudia Jonak (Vienna) discussed the role of the Arabidopsis S-phase Kinase Associated Protein 1 (SKP1)-like 5 (ASK5) kinase in linking adaptive regulation of the redox balance via control of the phosphorylation status of the pentose phosSymposia on plant (protein) phosphorylation