The miRNA-mediated post-transcriptional regulation of maize response to nitrate

Abstract

Stress responses depend on the correct regulation of gene expression. The discovery that abiotic as well as biotic stresses can regulate miRNA levels, coupled with the identification and functional analyses of stress-associated genes as miRNA targets, provided clues about the vital role that several miRNAs may play in modulating plant resistance to stresses. Nitrogen availability seriously affects crops productivity and environment and the understanding of the miRNA-guided stress regulatory networks should provide new tools for the genetic improvement of nitrogen use efficiency of crops. A recent study revealed the potential role of a number of nitrate-responsive miRNAs in the maize adaptation to nitrate fluctuations. In particular, results obtained suggested that a nitrate depletion might regulate the expression of genes involved in the starvation adaptive response, by affecting the spatio-temporal expression patterns of specific miRNAs.

Figure 1. Comparison of in situ hybridization signal detections of zma-miR528a/b obtained with LNA (A, C, E and G) or ZNA (B, D, F and H) 5′ end DIG labeled probes. Longitudinal sections of maize root apices (A and B), longitudinal sections of maize lateral roots primordia (C–F) and longitudinal sections of maize root differentiated zones (G and H) are reported. Six slides (including at least five sections each) per probe concentration (at least two probe concentrations were tested for each hybridization combination) per experimental condition were performed in order to obtain reliable hybridization signal. Among all the concentrations tested, the one corresponding to 20 nM was showed (cc, central cylinder; qc, quiescent center; pc, pericycle; ep, epidermis; cx, cortex). Scale bars 200 μm.

Figure 2. A graphic representation of localization of N-responsive miRNAs in a longitudinal section of both nitrate-supplied (+N) and nitrate-depleted (-N) maize roots. The apical meristem and the root cap of N-supplied seedlings are characterized by the strong expression of miR528a/b, while the vascular tissue is the site of expression of miRNA166j/k/n and miRNA169i/j/k. MiR408/b and miR528a/b were found in the epidermis cells of N-supplied apical meristem. Lateral roots are interested by the localization of all the four miRNAs showed. In general, hybridization signals became weaker in nitrate-depleted roots for all miRNAs investigated. Probe accumulations were not found in apical meristems or in lateral root primordia of N-depleted roots (ep, epidermis; v, vascular tissue; p, perycicle; lrp, lateral root primordia). Color codes of miRNAs are also indicated.