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J Philipp Benz
Soll Lab
LMU Munich; Dept. Biologie I, Plant Biochemistry; Grosshaderner Str. 2-4; Planegg-Martinsried
(+49-89) 2180-74758 o. -69
(+49-89) 2180-74752

In order to fulfil their functions correctly, plastids permanently communicate with the surrounding cell. This requires a substantial traffic of substances like nutrients, metabolites and proteins into and out of the organelle, which have funnelled across the two envelope membranes surrounding all plastid types. Among these transport processes, the translocation of proteins is of particular significance. Due to the loss of >90% of their genetic information to the host nucleus during evolution, plastids have become almost completely dependent on the surrounding cell. Of ~3000 proteins present in chloroplasts, typically only 50-250 (dependent on the species) are still encoded for on the plastome. The majority of proteins has therefore to be imported posttranslationally from the cytoplasm, which is most generally performed via two translocation machineries present in the outer (OEM) and inner envelope membrane (IEM), called TOC (translocon at the outer envelope of chloroplasts) and TIC (translocon at the inner envelope of chloroplasts), respectively. In this pathway, nuclear encoded preproteins are translated with an N-terminal extension called transit peptide, which allows targeting of the precursor to the organelle, specific recognition by the receptor proteins on the surface and subsequent translocation through both membranes as well as the intermembrane space (IMS). After successful import, the transit peptide is cleaved off by the stromal processing peptidase (SPP), resulting in the mature form of the protein.

The main focus of my group is the elucidation of the mechanism by which the Tic complex works and in particular how it is regulated.

Translocation across the envelope is surely a bottleneck in the path of transported proteins from the cytosol to their final destination in the chloroplast. The TIC and TOC translocons are therefore perfectly situated to impose a regulatory control over incoming preproteins. Additionally, since many signals of the chloroplast originate from the thylakoids and therefore have to be sensed inside the organelle, the IEM is closest to the origin of the signal, and thus regulation at the TIC complex could be one of the fastest ways to react efficiently.

The regulon of the complex consists of three proteins which all have redox-active properties (Tic62, Tic55, and Tic32), which makes a redox-regulation of the import process very likely. However, knowledge of this aspect so far is limited. To shed light onto the regulation of TIC, the central part of my project deals with Tic62, which has the intriguing potential to shuttle from the membrane-bound to a soluble state dependent on the redox condition of the chloroplast, making it the most interesting candidate for a redox sensor of the complex.

In addition to the shuttling behavior, its highly specific interaction with FNR (ferredoxin-NADP+-oxidoreductase), a key enzyme of photosynthesis, has been discussed as an important feature for the redox-regulation of preprotein import into the organelle, as it provides a link between photosynthetic electron transport (at the thylakoids) and protein translocation (at the envelope). However, the nature and function of the close relationship with FNR remains enigmatic.

To answer the open questions several experimental approaches are undertaken, making use of the model plant Arabidopsis thaliana in addition to Pisum sativum (pea). It could by now be verified that Tic62 is also located at the thylakoids itself - in addition to the known localization at the inner envelope. The acquired data furthermore demonstrate that Tic62 and FNR form several thylakoid-bound complexes of high molecular weight. Analysis of tic62 knockout plants revealed that FNR is severely disturbed at the mutant membranes. It can thus be concluded that Tic62 represents a major FNR interaction partner not only at the envelope and in the stroma, but also at the thylakoid membranes of vascular plants. Current work deals with the regulation of this intriguing new Tic62/FNR pool and how it is integrated into the photosynthetic, redox and import signaling network of the organelle.


  • 10.1998 - 08.2003: Studies of Biology at the Technical University Carolo- Wilhelmina at Braunschweig


  • 10.2002 - 08.2003: Preparation of the Diploma thesis in the lab of Prof. Dr. Nigel M. Crawford at the University of California at San Diego (UCSD), USA
Titel: "Analysis of the Transcriptional Regulation of the Dual-Affinity Nitrate Transporter Gene AtNRT1.1 (CHL1) from Arabidopsis thaliana"

  • 18.08.2003: Receiving of the academic degree: Diplom-Biologe (Grade: passed with distinction)
  • 11.2003 - 08.2004: Continued work in the lab of Prof. Dr. Nigel M. Crawford (at UCSD) in the position of a full scientific lab assistant


  • 10.2004 - 06.2009: PhD graduate student in the lab of Prof. Dr. J. Soll at the LMU Munich


  • 22.06.2009: Rigorosum (Grade: summa cum laude)


  • 06.2009 - 03.2010: Postdoc in the lab of Prof. Dr. J. Soll at the LMU Munich


  • 04.2010 - today: Postdoc in the lab of Prof. Dr. Chris R. Somerville at the Energy Biosciences Institute (EBI) at UC Berkeley (CA, USA)




  • Benz P, Soll J, Boelter B. (2007) The Role of the Tic Machinery in Chloroplast Protein Import in The Enzymes, Vol 25; Molecular Machines Involved in Protein Transport across Cellular Membranes (Dalbey R, Koehler C & Kamanoi F, eds.), Academic Press/Elsevier, 2007


  • Stengel A*, Benz P*, Balsera M, Soll J & Bolter B (2008) TIC62 Redox-regulated Translocon Composition and Dynamics. J Biol Chem 283, 6656-67 *(contributed equally)


  • Benz JP, Soll J, Bolter B (2009) Protein transport in organelles: The composition, function and regulation of the Tic complex in chloroplast protein import. FEBS J. 276 (5): 1166-76


  • Stengel A, Benz JP, Buchanan B, Soll J, Boelter B. (2009) Preprotein import into chloroplasts via the Toc and Tic complexes is regulated by redox signals in Pisum sativum. Molecular Plant Nov;2(6):1181-97


  • Stengel A, Benz JP, Buchanan B, Soll J, Boelter B. (2010) Redox regulation of protein import into chloroplasts and mitochondria: similarities and differences. Plant Signaling & Behavior, Feb;5(2):105-9


  • Benz JP*, Stengel A*, Lintala M, Lee YH, Weber A, Philippar K, Guegel IL, Kaieda S, Ikegami T, Mulo P, Soll J, Boelter B. (2009) Arabidopsis Tic62 and ferredoxin-NADP(H) oxidoreductase form light-regulated complexes that are integrated into the chloroplast redox poise, The Plant Cell Dec;21(12):3965-83 *(contributed equally)

POSTERS:

  • Benz JP, Soll J, Boelter B. Characterization of the Chloroplast TIC Complex. FEBS-EMBO Advanced Lecture Course: Cellular and molecular biology of membranes; 20.06.-01.07.2005; Cargese, Corse, F

  • Benz JP, Soll J, Boelter B. Purification and Characterization of the Translocon of the Inner Chloroplast Envelope. EMBO Conference: Protein transport systems: Protein targeting and translocation; 30.09-05.10.2006; Gdansk, PL

  • Stengel A, Benz JP, Soll J, Boelter B. Tic62 - New Insights Into Redox-regulated TIC Function and Composition. Gordon Research Conference: Protein transport across cell membranes; 10.6.-15.6.2007; Il Ciocco, IT

  • Benz JP, Stengel A, Soll J, Boelter B. Characterization of Tic62: a possible link between chloroplast preprotein import and photosynthesis? XVI Congress of the Federation of European Societies of Plant Biology (FESPB); 17.08.-22.08.2008; Tampere, FIN - Poster Award

TALKS:

  • "Tic62 - a link from photosynthetic e- transport to preprotein import?" Intl. Photosynthesis Workshop; 01.10.2008; Bichl, Germany


  • 02.2001 - 08.2003: Scholarship by the Studienstiftung des deutschen Volkes (German National Academic Foundation)


  • 10.2002 - 08.2003: Scholarship for studies abroad from the DAAD (Deutscher Akademischer Austausch Dienst e.V.; German Academic Exchange Service)


  • 08.2008: XVI Congress of the Federation of European Societies of Plant Biology (FESPB); Tampere, FIN - Best Student Poster Award

  • (Vice-)Treasurer
  • Organiser of the winter retreat 2007 to Oberaudorf
  • Organizer of the ENB Seminar feat. Bob Buchanan and Sheng Luan
  • Member of the program application taskforce ;-)
  • Organizer of the Scientific Journalism Seminar with H.Rehm (Laborjournal)


Postdoc at the EBI (Energy Biosciences Institute) at UC Berkeley

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J Philipp Benz
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