Metabolite sensing signal processors in eukaryotic photosynthetic microorganisms: from molecular mechanisms to cellular functions
Final Report Abstract
The PII signalling proteins are among the most widely distributed signalling proteins in nature, occurring in the domains of Bacteria, Archaea and Green Plants. In prokaryotes, they play a central role in the detection of the metabolic state of the cell, in particular, in the carbon-nitrogen balance. In a breakthrough work, we revealed in collaboration with the group of Prof. Elena Ermilova from the State University St. Petersburg, that in green plants, PII proteins act as sensors for the amino acid glutamine. This led us to hypothesize that PII proteins in oxygenic phototrophs (Algae) also play a role as central metabolic regulators. In this project, the group from St.Petersburg analysed the physiological consequences of PII-mediated signal transduction, with a special focus on biotechnological applications. Our group focused on molecular and mechanistic studies of plant PII signalling. The first part of our project addressed the question on the evolution of PII signalling in the course of the endosymbiotic generation of the chloroplast from cyanobacterial ancestors. Therefore, we investigated the structure-function relationship of PII proteins from various algal groups. According to our studies, the glutamine-sensing C-terminal extension emerged with the transfer of the glnB gene from the chloroplast into the core genome. During the entire process of evolution, the key enzyme of arginine synthesis, the N-acetyl-L-glutamate kinase (NAGK) acts as a major interaction partner of PII. In the case of Polytomella parva, PII was even converted into a stably bound subunit of NAGK. Our search for additional interaction partners of PII failed to identify reliable partners that interacted in vitro. Therefore, in a second study, we analysed with the help of fluorescently labelled reporters the co-localization of PII with various plastidic proteins in the model plant Arabidopsis thaliana. In essence, we could confirm the strong interaction between PII and NAGK in plastids. Moreover, we detected several weaker interactions with proteins, many of which are involved in the plastidic protein turn-over machinery. These data indicate that PII in Arabidopsis may be part of the plastidic protein degradation machinery.
Publications
-
(2018) The PII signaling protein from red algae represents an evolutionary link between cyanobacterial and Chloroplastida PII proteins. Scientific Reports
Lapina T., Selim K.A., Forchhammer K., Ermilova E.
-
(2019) Effects of arginine on Polytomella parva growth, PII protein levels and lipid body formation. Planta - 250, 1379–1385
Lapina T.V., Kochemasova L.Yu., Forchhammer K., Ermilova E.V.
-
(2019) Interaction of N-acetyl-L- glutamate kinase with the PII signal transducer in the nonphotosynthetic alga Polytomella parva: co-evolution towards a hetero-oligomeric enzyme. FEBS Journal
Selim K., Lapina T., Forchhammer K., Ermilova E.
-
(2020) From Cyanobacteria to Archaeplastida: New evolutionary insights into PII signalling in the plant kingdom. New Phytologist
Selim K., Ermilova E., Forchhammer K.
