Dissecting SBDS function in Arabidopsis thaliana

Abstract

Ribosome biogenesis has been extensively studied across various organisms, yet its complex mechanisms in plants remain underexplored. The SBDS protein, a highly conserved factor across eukaryotes, is essential for ribosome maturation and function. Interestingly, the Arabidopsis thaliana SBDS (AtSBDS) protein has a unique C-terminal zinc finger extension that distinguishes it from homologues in other organisms. This research aims to elucidate the role of the SBDS protein in plants, with a particular focus on this zinc finger domain. I hypothesise that the zinc finger domain of AtSBDS interacts with eIF6, similar to homologues Rei1 and Vms1, potentially contributing to its eviction from the 60S ribosomal subunit as part of a ribosome quality control system. Furthermore, I propose that this domain plays a critical role in ribosome biogenesis and plant viability. Using A. thaliana as a model organism, this study investigates the functional role of AtSBDS protein, with a particular focus on its distinctive zinc finger extension. A multidisciplinary approach, integrating genetic, biochemical, and structural biology techniques, has been employed to elucidate its functions and address the central hypothesis of this research. Three formal results chapters present data on AtSBDS, including: 1) the genetic analysis of AtSBDS localisation and the effect of hypomorphic mutations on plant viability, along with functional characterisation of the zinc finger extension, demonstrating its indispensability for plant development; 2) biochemical analyses, including NMR and proteomic studies, which provide direct evidence of an interaction between AtSBDS and eIF6 mediated by the zinc finger domain, with cross-species experiments using Dictyostelium discoideum conditional SBDS mutants offering insights into the evolutionary conservation of SBDS function; and 3) preliminary cryo-EM data, which provide the first visualisation of A. thaliana ribosomal subunits and reveal AtSBDS and AteIF6 bound to the ribosome, offering new insights into ribosome assembly and function in plants. This research aims to bridge the gap in our knowledge about ribosome biogenesis in plants by showing the molecular details of AtSBDS function and its broader biological implications, thus contributing to our understanding of ribosome assembly and regulation in plants. By advancing our knowledge of the unique contributions of the AtSBDS zinc finger domain, this study lays the foundation for future research on ribosome dynamics in plants, with potential applications for improving plant growth and agricultural resilience.