Cyanophora paradoxa, the key to plastid evolution
Phototrophic eukaryotes (algae) originated about 1.2 billion years ago through the so-called primary endosymbiotic event: a heterotrophic protist engulfed a cyanobacterium without digesting it. Instead, the host cell made use of the photosynthesis products generated by the endosymbiont and, in a lengthy and very complicated process, prevented its escape through inducing gene transfer from the genome of the former free-living cyanobacterium to the nucleus. In parallell, a selective protein import apparatus was developed at the endosymbiont envelope and many but not all of the exported genes were “reimported” as proteins.C. paradoxa merits the status of a ”living fossil” since the plastids (“muroplasts”, formerly named “cyanelles”) are stabilized by a peptidoglycan wall between the two envelope membranes – a situation resembling the envelope of cyanobacteria and unique (i.e., restricted to Glaucocystophyte algae) among eukaryotes (Fig. 1). The majority of researchers in the field assume a single primary endosymbiotic event, i. e. monophyly of the kingdom Plantae and we contributed phylogenetic analyses of muroplast and nuclear genes (Fig. 2, collaboration with Franz Lang and Hervé Philippe, Montreal). Other acivities in the past years.
dealt with the targeting sequences and the translocons involved in protein import into muroplasts. For comparison, proteins targeted into the secondary plastids of Euglena gracilis were inspected. Furthermore, the presence of a carbon-concentrating mechanism and, potentially, of carboxysomes in muroplasts of C. paradoxa was demonstrated (collaboration with Hans J. Bohnert, Tucson and Hideya Fukuzawa, Kyoto). Carboxysomes are Rubisco-microcompartments known from cyanobacteria but not from algae. The carboxysomal CCM leads to an enrichment of bicarbonate in the cytosol by a factor of several thousands. The presence of a carboxysome in muroplasts would explain the maintenance of the peptidoglycan wall - as a stress-bearing layer. Now, we participate in the Cyanophora genome project (head: Debashish Bhattacharya, Rutgers Univ.). At present, the draft genome (around 70Mb) is subject to analysis and we concentrate on genes for peptidoglycan synthesis, Sec, Tat, Toc and Tic translocons, phycobilisome subunits, and potential components other than Rubisco and Rubisco activase (the latter was recently identified by us) of the putative carboxysomes.
Ph. D. (Chemistry/Physics, University of Vienna, 1972)
Habilitation 1982 (Biochemistry)
Associate Professor 1991
Theodor Körner Prize 1976
Research Prize of the City of Vienna 1982
Head, Ludwig-Boltzmann Research Unit of Biochemistry (2001-2005)
Vice-head, Department of Biochemistry (2005 - 2008)
Retired since October 2008.
"Kurt-Mothes-Gastprofessor" at the Martin-Luther-University Halle/Saale (September - November 2009)
Steiner JM, Bhattacharya D, Löffelhardt W (2012) Conservative sorting in the muroplasts of Cyanophora paradoxa: a reevaluation based on the completed genome sequence. Symbiosis DOI 10.1007/s13199-012-0203-1
Price DC, Chan CX, Yoon HS, Yang EC, Qiu H, Weber APM, Schwacke R, Gross J, Blouin NA, Lane C, Reyes-Prieto A, Durnford DG, Neilson JAD, Lang BF, Burger G, Steiner JM, Löffelhardt W, Meuser JE, Posewitz MC, Ball S, Arias MC, Henrissat B, Coutinho PM, Rensing SA, Symeonidi A, Doddapaneni H, Green BR, Rajah VD, Boore J and Bhattacharya D (2012) Cyanophora paradoxa genome elucidates origin of photosynthesis in algae and plants. Science 335, 843-847.
Löffelhardt W (2011) The chlorarachniophyte nucleomorph is supplemented with host cell nucleus-encoded histones. Mol. Microbiol. 80: 1413–1416.