Elucidating an Arabidopsis N-Responsive Gene Regulatory Network

Nitrogen (N) is essential for plant growth and metabolic processes. The use of N-containing fertilisers helped to improve crop yield over the past few decades but had negative impacts on the environment. In response to changes in N availability, plants alter the expression of thousands of genes coordinated by a complex network of transcription factors. Previous work has identified a putative sub-network of transcription factors that are hypothesized to coordinate the large transcriptional response to changes in nitrate. However, the roles of the numerous TFs that comprise the network, many of which appear to work in feed-forward loops (FFLs) and to function epistatically, are unclear. In this project, we aim to characterise this sub-network, understanding how it coordinates plant growth in response to nitrate and to develop technologies that enable the rational engineering of N-use efficiency. Using in vitro and in vivo assays, we have investigated connections in the sub-network, identifying physical interactions and regulatory consequences (repression or activation). This has identified a key FFL that we hypothesise coordinates root growth in response to nitrate by modulating auxin signalling. Our results demonstrate how the components within this sub-network interact with each other and explain the phenotypes observed in loss-of-function mutations. It also provides a model for engineering plant N-responses using gene editing and network rewiring.