Elucidating the Role and Regulatory Networks of the putative DCAF protein WDR55 in Plant Reproductive Development

Sexual reproduction in flowering plants addresses the processes that give rise to seed and fruit production. This network of flower organization, gametogenesis and double fertilization is in particularly sensitive to environmental stresses such as elevated temperature and water restriction. Therefor research focused on these processes is of key strategic relevance in maintaining and enhancing crop yield. In addition, reproductive development has become a well-established model system to identify and study essential cell cycle and plant growth regulators. Those studies showed that while our current understanding of plant development is mainly based on different levels of transcriptional regulation, including the various roles of chromatin and the distribution of hormone gradients, the post transcriptional regulatory network seems to be even more complex while at least equally important. WDR55 is one of these essential proteins that was identified as necessary for reproductive development while being at the same time fundamental for growth, proliferation, bilateral symmetry and hormone signaling. Bjerkan et al. showed that WDR55 is a potential substrate receptor in a DDB1-CUL4-based E3 ubiquitin ligase complex and thus probably involved in targeting proteins for degradation. Using target and interactor screens for WDR55 we aim to identify and study its molecular network in plant reproductive development. These experiments will be complemented by a genetic and molecular dissection of wdr55 mutant plants. In addition, we will investigate the evolutionary role of WDR55 in eukaryotes through a bioinformatics approach, and this enables us to finally test the translational value of Arabidopsis gained knowledge into the crop model rice. Our results reveal and describe a highly conserved post-transcriptional mechanism that is able to adjust the fine structured network of the reproductive organs to diverging intrinsic and environmental signals. We show that the protein WDR55 mediates diverse tissue-specific gene expression in different plant organs. Comparing these plant organs identified a common identical modular structure of their expression networks. Further revealing a robust and redundant module that functions as a readout for growth signals and enables the expression network to react immediately to fluctuating growth conditions such as nutrition or temperature changes. We think that these results can be used in crop breeding research and promise agricultural benefits even under harsh growth conditions. Furthermore, since the the underlying mechanism is highly conserved between eukaryotes, a future potential for an interdisciplinary approach between plant, animal and experimental medicine can be envisioned.

The project has -strengthened molecular plant research by enhanced competence and skills, teaching and practice on new technical methods -facilitated building a network of in house-, within the Norwegian plant network- and international collaborations -facilitated increased interdisciplinary research collaboration both nationally and internationally -due to its state-of-the-art molecular methodology, been a flagship in disseminating plant biology to the public, giving impact for public education, awareness and inspiration (In a society where molecular editing of plants is possible, increased knowledge of plant biology become more relevant) -scientific outcomes with a potential impact to create new research areas in post transcriptional regulation of developmental and physiological processes and influence currently ongoing research projects in the field of plant developmental biology but also in a broader context, by interdisciplinary approaches in medical and breeding research

This project seek to identify and elucidate the role of novel regulators in plant development. Our current knowledge is mainly focused on different levels of transcriptionally based regulation, including the various roles of chromatin and the distribution of hormone gradients. However, the action of regulatory proteins are also regulated by proteolysis, and a major route is through the UBIQUITIN-26S proteasome (UPS)-dependent pathway. More than 5% of the Arabidopsis proteome consists of components of the UPS pathway, and with growing evidence of proteolytic and nonproteolytic roles of ubiquitylation, this regulation system thus rivals the role of transcription as the foremost regulatory mechanism. The WDxR motif containing protein, WDR55 has been identified by its requirement in seed development and plant reproduction. WDR55 interacts with DDB1A and is therefore a potential substrate receptor for a DDB1-CUL4-based E3 ubiquitin ligase complex. In this project we will elucidate the biological role of WDR55 by mutant studies and in biochemical and genome-wide approaches identify targets as well as components of the complex through which WDR55 acts. Additionally, we will investigate the evolutionary role of WDR55 in eukaryotes through a bioinformatics approach, and finally, test the translational value of Arabidopsis gained knowledge into the crop model rice. We expect the project to deliver major novel insights inthe role of proteolytic or non-proteolytic regulation throughout eukaryotes.