Physiological characteristics and RNA sequencing in two root zones with contrasting nitrate assimilation of Populus × canescens

Different root zones have distinct capacities for nitrate (NO3−) uptake in Populus species, but the underlying physiological and microRNA (miRNA) regulatory mechanisms remain largely unknown. To address this question, two root zones of Populus × canescens (Ait.) Smith. with contrasting capacities for NO3− uptake were investigated. The region of 0–40 mm (root zone I) to the root apex displayed net influxes, whereas the region of 40–80 mm (root zone II) exhibited net effluxes. Concentrations of NO3− and ammonium (NH4+) as well as nitrate reductase activity were lower in zone II than in zone I. Forty one upregulated and twenty three downregulated miRNAs, and 576 targets of these miRNAs were identified in zone II in comparison with zone I. Particularly, growth-regulating factor 4 (GRF4), a target of upregulated ptc-miR396g-5p and ptc-miR396f_L + 1R-1, was downregulated in zone II in comparison with zone I, probably contributing to lower NO3− uptake rates and assimilation in zone II. Furthermore, several miRNAs and their targets, members of C2H2 zinc finger family and APETALA2/ethylene-responsive element binding protein family, were found in root zones, which probably play important roles in regulating NO3− uptake. These results indicate that differentially expressed miRNA–target pairs play key roles in regulation of distinct NO3− uptake rates and assimilation in different root zones of poplars.

Nitrogen Starvation Differentially Influences Transcriptional and Uptake Rate Profiles in Roots of Two Maize Inbred Lines with Different NUE

Nitrogen use efficiency (NUE) of crops is estimated to be less than 50%, with a strong impact on environment and economy. Genotype-dependent ability to cope with N shortage has been only partially explored in maize and, in this context, the comparison of molecular responses of lines with different NUE is of particular interest in order to dissect the key elements underlying NUE. Changes in root transcriptome and NH4+/NO3− uptake rates during growth (after 1 and 4 days) without N were studied in high (Lo5) and low (T250) NUE maize inbred lines. Results suggests that only a small set of transcripts were commonly modulated in both lines in response to N starvation. However, in both lines, transcripts linked to anthocyanin biosynthesis and lateral root formation were positively affected. On the contrary, those involved in root elongation were downregulated. The main differences between the two lines reside in the ability to modulate the transcripts involved in the transport, distribution and assimilation of mineral nutrients. With regard to N mineral forms, only the Lo5 line responded to N starvation by increasing the NH4+ fluxes as supported by the upregulation of a transcript putatively involved in its transport.