Sucrose controlled translation mediated by a sequence conserved peptide in Arabidopsis thaliana

Abstract

The sessile nature of plants demands adaptation to a variety of external stimuli. Sugars have well established roles in steering growth and developmental processes, and sugar levels are a good proxy for the energy status in plants. Molecular sugar signaling networks perceive the availability of sugars and relate this information to key plant processes. For example, global gene transcription and translation is sensitive to sugars. Ample availability of sugars allows for investment in growth, while low energy stress induced by biotic and abiotic signals necessitates reduced investment in energy demanding processes such as cell division and protein synthesis. Understanding the fundamental molecular mechanisms involved in sugar signaling provides opportunities for improving plant biomass accumulation and growth of harvestable organs. Plant adaptations in response to the energy status involve the activities of the Target of Rapamycin (TOR)-kinase and Snf1-related kinase 1 (SnRK1). While plant TOR kinase promotes growth in response to high sugar levels, SnRK1 is particularly active upon sugar deprivation. Both kinase signaling networks are important throughout the plant’s lifecycle. In the angiosperm model plant Arabidopsis thaliana, S1-class basic leucine zipper (bZIP) transcription factors mediate the response to various stresses and regulation of gene expression by these factors involves the activity of both TOR and SnRK1, indicating a central role in energy signaling. Translation of S1-bZIP genes is specifically repressed in response to sucrose. Sucrose induced repression of translation (SIRT) of S1-bZIP genes is mediated by a sequence conserved sucrose control (SC) peptide, encoded in the gene leader sequence. The work described in this thesis provides a better understanding of the role of TOR kinase in S1-bZIP gene expression, and provides a foundation for the identification of molecular plant factors that are essential for the regulation of SIRT. By chemical library screening, several compounds were identified that disrupt SIRT in vivo. In addition, it was discovered that SIRT is mediated by gene sequences from plant species other than Arabidopsis, and this observation suggests that the SIRT mechanism of translation regulation is important for the development of different plant species.