Streptophyte algae and the evolution of nuclear control over plastid function

• Applicant: Professor Dr. Jan de Vries
• Subject Area: Evolution and Systematics of Plants and Fungi
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 324438572

Land plants dominate the terrestrial macroscopic biome. Over the last few years, researchers have begun to appreciate that many features of plant biology that were once deemed land-plant specific in fact evolved in their algal progenitors, the streptophyte algae. Among the list of features that are believed to have supported the streptophyte algae during the transition to land are hormonal stress response signalling, communication with beneficial soil microbionts, protection against exposure to UV radiation and the presence of specialised cell walls. The latter are especially crucial for important plant traits such as tolerance to the terrestrial stressors high light and drought. These factors, however, also have a direct impact on the photosynthetic organelles, the plastids (chloroplasts). Although interest in streptophyte algae and the exaptations that faciliated the transition to land is growing, the role of the plastid in the shift to terrestrial life has not been considered in an experimental fashion. The plastids of higher branching streptophyte algae are more similar to those of land plants than to those of lower branching ones or those of other algae. Concomitantly, higher branching streptophyte algae show signs of increased nuclear control over plastid function by virtue of gene loss and transfer to the nucleus. What is more, preliminary genomic data reveal a growing repertoire of nuclear factors regulating plastid transcription and response to plastid signals within streptophyte algae. Here I propose to investigate the streptophyte algal origin of embryophyte plastids, culminating in the versatile organelle of vascular plants that can differentiate into amyloplasts, chromoplasts and many others. The evolution of plastid-nucleus communication will be analysed through global gene expression profiling of one representative from each major streptophyte algal group. Algae will be cultivated under controlled growth regimes and differential gene expression will be explored through perturbation of plastid function with high light and cold treatments. I will focus on the differential expression of genes for plastidal proteins (anterograde) and plastid to nucleus (retrograde) signalling factors. This proposal will conduct the first systematic survey of plastid-nucleus communication in streptophyte algae, with the goal of exploring the stepwise evolution of plant plastid-nucleus communication in streptophytes. At the same time crucial data on the molecular physiology of streptophyte algae will be generated. These data will allow me to test the hypothesis that the present degree of nuclear control over plastid function in plants emerged during streptophyte evolution, a shift from organelle to nucleus that played a critical role in the emergence of plant life on Earth.

• DFG Programme: Research Fellowships
• International Connection: Canada
• Host: Professor John M. Archibald, Ph.D.