Post-Translational Control of CRFs in Plant N Signalling

Nitrogen (N) is the main mineral nutrient for plants as a basic component of many different molecules required for plant cells and organs to function. How much N is available in soil, and in what chemical form, is a key limiting factor for how well plants can grow. This is why farmers rely on N- rich fertilisation when trying to increase the yield of their crops. However, plants are not very efficient in utilizing the N fertiliser provided, and increasing N supply only partially increases productivity. Instead, excess N often leaches from soils polluting the environment. This is a big problem, and to solve it, we need to understand in detail how plants react to changes in N supply. Plants take up N from soils in two main forms, nitrate and ammonium. In most environments, plants prefer N in the form of nitrate. Interestingly, nitrate is not only a nutrient, it also coordinates important processes within the plant in its role as a signalling molecule. Together with the two key plant hormones auxin and cytokinin, and other regulatory networks in plant cells and tissues, nitrate influences how cells grow and differentiate, how roots and shoots are formed, and how seeds are produced. All of these help plants to continuously adapt to changes in the environment. My focus is on a group of plant-specific proteins called Cytokinin Response Factors (CRFs). We know that different CRFs are involved in organ development mediated by the plant hormones auxin and cytokinin, as well as in adaptive responses to the environment. Using the laboratory model plant Arabidopsis thaliana, our group has observed that CRFs play an important role in how plants adapt to changes in N source. But we do not know yet how these regulators integrate nitrate and hormonal signals. To elucidate this, I will combine approaches from cell biology, genetics, proteomics, and plant physiology, and I will use the latest tools for microscopy of living plants, protein identification, and quantification. Reducing pollution from excessive N fertilisation is one thing but if we want to ensure sufficient and nutritious food production globally, we also need to optimize how efficiently plants use N in increasingly harsher environments, leading to more productive crops. Better understanding of CRF activity can shed new light on some of the key processes involved.