Cellular acclimation and signal transduction of the green alga Chlamydomonas reinhardtii under anaerobic conditions

• Applicant: Privatdozentin Dr. Anja Christine Hemschemeier
• Subject Area: Plant Biochemistry and Biophysics ; Plant Genetics and Genomics ; Plant Cell and Developmental Biology
• Term: from 2013 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 235088911

In the absence of molecular oxygen (O2), aerobic organisms have to generate sufficient energy via the inefficient substrate level phosphorylation while adjusting growth to impaired biosynthetic pathways. The acclimation to anaerobiosis is facilitated by altered substrate- and electron fluxes as well as the differential expression of genes. This project aims at analyzing the response of the unicellular green alga Chlamydomonas reinhardtii to the stress condition of anaerobiosis on metabolic and transcriptional levels.Genome-wide transcript profiles from anaerobic C. reinhardtii cultures which we obtained by RNA-sequencing resulted in the identification of two candidate genes. One of the encoded proteins, THB8, belongs to the family of truncated hemoglobins. We could already observe that post-transcriptional silencing of the THB8-gene results in C. reinhardtii transformants which hardly grow under anaerobic conditions in the light and in which several anaerobic key genes are not properly expressed. In view of the phenotype of the transformants and a nitric oxide- (NO-) binding capacity of recombinant THB8 we postulate that THB8 is involved in an NO-based signaling transduction pathway. The expression patterns of the THB8-knockdown transformants indicate a connection between a proper THB8 expression and anaerobic induction of the CYG12 gene which encodes a heme/NO-binding guanylate cyclase. CYG12 was also outstanding in the above mentioned whole-genome transcript profiles.During this project, the postulated NO-based signaling cascade will be examined by determining the biochemical and biophysical features of THB8 and CYG12 as well as by analyzing the physiological and genetic characteristics of THB8- and CYG12-knockdown strains. The biochemical part of this project will focus on characterizing the heme groups, the binding of ligands such as NO and on identifying interaction partners of THB8 and CYG12. This project part will also include the analysis of a fermentative enzyme, the pyruvate:ferredoxin oxidoreductase PFR1. According to our RNA-Seq data, the regulation of the PFR1 gene differs significantly from other genes involved in fermentation. The biochemical and biophysical characteristics as well as the possible reactions catalyzed by PFR1 will hopefully elucidate its physiological role and thereby give clues to the reason for the different PFR1 gene expression.The physiological-genetic part of this study will focus on the characterization of physiology and (NO-dependent) gene expression upon anaerobiosis of the THB8- and yet to be created CYG12-knockdown transformants. A major part of this project will the generation of whole genome transcript profiles of the knockdown strains in order to identify affected gene groups.

• DFG Programme: Research Grants