Nutrient-Responsive Plant Micrornas

Being sessile, plants have to cope with many adverse environmental changes, including changing nutrient availability. Adequate availability of mineral macronutrients (e.g., N, P, K, S) and micronutrients (e.g., Cu, Fe, Zn) in the soil and their acquisition are vitally important for plant growth, development, and reproduction. Too little or too much of the nutrients negatively affects these traits and hence plant fitness and survival. Therefore, cellular concentrations of these nutrients have to be maintained at physiological levels, and adaptive physiological or developmental responses need to be initiated if necessary. Over the last few years, some nutrient-responsive microRNAs (miRs) have been discovered primarily in the model plant species Arabidopsis thaliana (A. thaliana), and several quickly evolved as critical components in scenarios such as regulation of plant P, S, or Cu homeostasis, or plant developmental adaptations to N availability. Several of these nutrient-responsive miRs also were found in phloem, i.e., the conductive vessels of plants, and a few were shown to act as systemic, long-distance signals. The presence of these miRs, their conserved nutrient response, and target genes in many higher plant species suggest deep conservation of the regulatory mechanisms. This chapter highlights and summarizes these discoveries.