Root Responses to Heterogeneous Nitrate Availability are Mediated by trans-Zeatin in Arabidopsis Shoots

Abstract

Plants are subjected to variable nitrogen (N) availability including frequent spatial nitrate (NO3-) heterogeneity in soil. Thus, plants constantly adapt their genome expression and root physiology in order to optimize N acquisition from this heterogeneous source. These adaptations rely on a complex and long-distance root-shoot-root signaling network that is still largely unknown. Here, we used a combination of reverse genetics, transcriptomic analysis, NO3- uptake experiments and hormone profiling under conditions of homogeneous or heterogeneous NO3- availability to characterize the systemic signaling involved. We demonstrate the important role of the trans-zeatin form of cytokinin (CK) in shoots, in particular using a mutant altered for ABCG14-mediated trans-zeatin-translocation from the root to the shoot, in mediating: (i) rapid long distance N-demand signaling and (ii) long term functional adaptations to heterogeneous NO3- supply, including changes in NO3- transport capacity and root growth modifications. We also provide insights into the potential CK-dependent and independent shoot-to-root signals involved in root adaptation to heterogeneous N availability.

RETRACTED: Cytokinin and abiotic stress tolerance -What has been accomplished and the way forward?

“…Many studies have identified WUS as a primary target gene of RRBs (type-B response regulator proteins), suggesting a shorter signalling channel in the responsive meristem, which is consistent with cytokinin working via altering WUS activity (Dai et al, 2017). Poitout et al (2018) determined that the ABCG14 transporter plays a critical role in the export of nitrate-induced cytokinin from roots, based on the fact that its mutation affected systemic N (nitrogen) signalling. Furthermore, they discovered a significant transcriptional reprogramming in shoots mediated by root-derived cytokinin, indicating that the hormone has functions beyond regulating SAM activity (Poitout et al, 2018).…”

“…Subsequently these findings imply that cytokinin has a role in the regulation of As and Se stress adaption. Cytokinins capacity to regulate plant development in response to nutrient stress was demonstrated in recent research on the role of cytokinin in signaling the availability of nitrogen (N) from the roots to the shoots (Landrein et al, 2018;Poitout et al, 2018). The expression of a GFP reporter gene under the control of WUS promoter, that governs the expression of a key regulator of shoot apical meristem (SAM) activity, was measured using quantitative microscopy (Landrein et al, 2018).…”

“…Poitout et al (2018) determined that the ABCG14 transporter plays a critical role in the export of nitrate-induced cytokinin from roots, based on the fact that its mutation affected systemic N (nitrogen) signalling. Furthermore, they discovered a significant transcriptional reprogramming in shoots mediated by root-derived cytokinin, indicating that the hormone has functions beyond regulating SAM activity (Poitout et al, 2018). NLP transcription factors (TF), which act as positive regulators of CYP735A and IPT gene expression, are involved in the increase of cytokinin levels in the root in response to changes in nitrate availability.…”

Effect of ammonia-oxidizing bacterial strain that survives drought stress on corn compensatory growth upon post-drought rewatering

“…High rhizosphere soil nitrification rate caused the continuous release of more NO − 3 from the soil during the rewatering period, increasing the stimulation by NO − 3 in the roots. Soil NO − 3 can stimulate roots to synthesize cytokinins in various plants (Landrein et al, 2018;Poitout et al, 2018). As a result, more root cytokinins are synthesized and continuously delivered to increase the leaf cytokinin content in the DI.…”

Perennial grass root system specializes for multiple resource acquisitions with differential elongation and branching patterns

“…Split-root studies are commonly used to investigate localized effects of belowground environments on root systems. Many studies have identified differential branching patterns and elongation in response to heterogeneous nutrient supply (Drew et al, 1973;Gersani and Sachs, 1992;Dundabin et al, 2002;Linkohr et al, 2002;Ruffel et al, 2011;Poitout et al, 2018). Ruffel et al (2011) described a "dormant foraging strategy" characterized by suppressed lateral root development for portions of Arabidopsis seedling root systems growing with low nitrogen (N) availability in contrast to "active foraging" in portions growing with high N availability.…”