Abstract
In response to varying nutrient availability in soil, plants display a high degree of physiological and developmental plasticity that relies on both local and systemic signaling pathways to coordinate the expression of genes involved in adaptive responses. The integration of these responses at the whole-plant level requires long-distance signaling mechanisms communicating the information between the two indispensable organs, the shoot and the root, which respectively provide photosynthates and mineral nutrients. Although such long-distance signaling is not well understood at the molecular level, several molecules, including hormones, sugars, and nutrients themselves or their metabolites, have been suggested to function as the systemic signals. Moreover, recent discoveries of the phloem-mobile microRNA399s as key components mediating the plant responses to phosphorus stress reveal a novel biological role of small RNA in the long-distance signaling of nutrient status. © 2009 Elsevier Ltd. All rights reserved.