Macronutrient sensing and signaling in plants

Plants face different nutrient limitations during their lifecycles that can occur in agriculturally used soils, as well as in natural habitats. Growth, reproduction, and yield are often limited by the essential macronutrients phosphorus, nitrogen, potassium, calcium, magnesium, and sulfur. Due to the sessile nature of plants, it is essential for them to sense their environmental and internal nutrient levels, in order to allow proper responses to temporal and permanent limitations, and to adapt growth to the resources available. During recent years the function of a number of the macronutrient sensing and signaling networks have been clarified and especially the response to phosphate deficiency is now relatively well understood. Plant responses to limitations involve nutrient recycling, altered uptake, transport and translocation, changes in root system architecture, nutrient mobilization from the rhizosphere by the secretion of secondary metabolites, the use of alternative metabolic pathways, and the formation of plant–microbe/fungal symbiosis to increase nutrient uptake. These morphological and physiological adaptations are under tight control of complex sensing and signaling networks that enable plants to measure external and internal nutrient levels and to integrate resource availability with nutrient requirements in different plant parts. This chapter will summarize current knowledge on the role of sensing and signaling pathways in coordinating local and systemic responses to environmental fluctuations in macronutrient availability.