Evolutionary adaptations of the plastid transcription machinery as one key element in plant terrestrialisation

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Evolutionary emergence of land plants (the backbone of the terrestrial biosphere) traces back to a singular event in which freshwater algae conquered land, a process referred to as terrestrialisation. This transition to land required a plethora of molecular adaptations that allowed the ancestor of plants to survive under the harsh environmental conditions of the new habitat. One of the most important requirements was the physiological adaptation of the chloroplast that is especially susceptible to environmental stressors. Key element of this process was the coordination of gene expression between cell nucleus and organelle in order to guarantee proper build-up and maintenance of the photosynthetic machinery. This research proposal focusses on the evolution of the plastid transcription machinery and its multiple novel protein components proposing it as crucial evolutionary innovation during and for terrestrialization. The function and regulation of the eubacterial plastid RNA polymerase (PEP) inherited from the cyanobacteria-like progenitor was supplemented with additional PEP associated proteins (PAPs) and novel sigma factors and further put under the control of a nuclear encoded phage-type RNA polymerase (NEP). Most of these protein factors evolved in streptophyte algae and a complete set of the corresponding genes appeared for the first time in Chara braunii. The project combines phylogenetic, molecular-genetic and biochemical approaches. It investigates the precise phylogenetic appearance of these components, their evolutionary adaptations within various streptophyte model organisms (including a dual nucleo-plastid localization for bi-partite gene regulation) and the structural evolution of the PEP complex.