The Elongator protein complex integrates regulation of transcription and translation during photomorphogenesis in Arabidopsis thaliana

Elongator is the six subunit protein complex showing strong structural conservativeness. In plants, Elongator was described in many independent reports as located and active both in nucleus and in cytoplasm. In agreement with the nuclear localization, the best known role of the complex in plants is regulation of transcription, modulating expression of genes related to immune response, auxin signaling, cell cycle and circadian clock. However, there are also convincing reports explaining cytoplasmic localization and proving that plant Elongator modifies tRNAs. Thus, despite almost twenty years of research on plant Elongator, it is still not clear what is the true role of the complex in this kingdom. The main goal of this project is to show that Elongator in Arabidopsis regulates photomorphogenesis shaping gene expression both at transcription and translation level. Light triggers photomorphogenesis program in plant development, in which hypocotyl elongation is inhibited, while the apical hook opens and cotyledons expand. Arabidopsis plants having mutations in genes encoding various subunits of the Elongator complex (elo mutants) show photomorphogenesis defect known as light hyposensitivity (elongated hypocotyls, reduced angle between cotyledons and hyponastic growth of the cotyledons). So far, only the transcription- related activity of Elongator has been an object of our research devoted to understand how the complex regulates photomorphogenesis. Currently, our working hypothesis is that Elongator works at the interface of transcription and translation to integrate these processes and shape photomorphogenesis. We will apply bioinformatic analysis to select transcripts with highest content and strong bias for codons recognized during translation by tRNAs modified by Elongator. These predictions will be verified by ribosome profiling in elo and one of thiolation defective mutants which will allow to detect transcripts undergoing translation slow-down. Overlap between identified in this experiment transcripts and respective proteins identified by differential proteomics will allow to define the physiological role played by translation fine-tuning provided by Elongator during photomorphogenesis. Results of ribosome profiling, transcriptomics and proteomics of the analyzed mutants will be aligned to distinguish between genes/transcripts/proteins regulated by Elongator during transcription and/or translation or showing affected expression due to indirect effects. This research will contribute to understanding the range and interplay of two roles played by plant Elongator during transcription and translation.