Modulation of root growth by nutrient-defined fine-tuning of polar auxin transport

Nitrogen is an essential macronutrient and its availability in soil plays a critical role in plant growth, development and impacts agricultural productivity. Plants have evolved different strategies to sense and respond to heterogeneous nitrogen distribution. Modulating root system architecture, including primary root growth and branching, is among the most essential plant adaptions to ensure adequate nitrogen acquisition. However, the immediate molecular pathways coordinating the adjustment of root growth in response to varying nitrogen sources are poorly understood. Here, using a combination of physiological, live in vivo high- and super resolution imaging, we describe a novel adaptation strategy of root growth on available nitrogen source. We show that growth, i.e. tissue-specific cell division and elongation rates are fine-tuned by modulating auxin flux within and between tissues. Changes in auxin redistribution are achieved by nitrogen source dependent post-translational modification of PIN2, a major auxin efflux carrier, at an uncharacterized, evolutionary conserved phosphosite. Further, we generate a computer model based on our results which successfully recapitulate our experimental observations and creates new predictions that could broaden our understanding of root growth mechanisms in the dynamic environment.