O-glycosylation during Plant Development

Plant development and aging are regulated by a complex interplay of internal developmental programs with changing environmental inputs. In order to integrate environmental with internal signals, proteins within cells are often temporary modified to change their function, allowing for fine-tuning during development and adaptation to changing environments. One of these protein modifications is the attachment of sugars (protein glycosylation), which is essential in many organisms including plants, but its function and regulation are not well understood as yet. During our work on the role of a specific type of protein glycosylation during flowering, we found that plants lacking the ability to perform this type of glycosylation show accelerated aging, in that they transition quicker from the juvenile to the adult and reproductive (flowering) phase during their life cycle. This process is also strongly regulated by a microRNA (miR156) and its target proteins SPLs, a family of transcription factors that determine the activity of genes that regulate plant development. We observed genetic interactions between glycosylation and SPL transcription factors, leading to strong effects in leaf growth, shoot branching and embryo development. However, our results also open a number of questions, and the mechanism behind the interaction between glycosylation and the miR156 regulated SPLs remains unclear. In the current project we therefore propose a number of experiments to tackle these questions, using a combination of genetic analysis and biochemistry. We aim to specifically unravel whether the observed effects on plant development result directly from glycosylation of SPL proteins, or if they are due to effects of other, independent cellular signaling pathways. We will also analyze if the important plant hormone gibberellin plays a role in this context. The miR156-dependent process of plant aging and SPLs regulate a number of highly important agronomic traits, including flowering time, shoot branching and consequently crop yield. Our data will contribute to the understanding of how SPLs - and thus these plant traits - are regulated. Additionally, this work will not only clarify specifically the role of glycosylation in the miR156- dependent aging pathway, but more generally shed a light on the molecular function of protein glycosylation of transcription factors and the integration of different signaling pathways during plant development.