Long‐distance nitrate signaling displays cytokinin dependent and independent branches

Abstract

Summary The long‐distance signaling network allowing a plant to properly develop its root system is crucial to optimize root foraging in areas where nutrients are available. Cytokinin is an essential element of the systemic signaling network leading to the enhancement of lateral root proliferation in areas where nitrate is available. Here, we explore more precisely: (i) which particular traits of lateral root growth (density and length of emerged lateral roots) are the targets of systemic signaling in a context of heterogeneous nitrate supply; and (ii) if the systemic signaling depends only on cytokinin or on a combination of several signalings.

Cytokinin at the Crossroads of Abiotic Stress Signalling Pathways

“…The signalling components that are involved in nitrate-upregulated cytokinin biosynthesis are the nitrate transporter-receptor NRT1 ( NPF6.3 ) acting upstream of IPT3 [16], and the NLP-NIGT1 transcriptional cascade controlling CYP735A2 and IPT3 expression [17]. Cytokinin also participates in nitrate foraging, which involves plants’ preferential development of lateral roots in nitrate-rich areas, thereby maximizing nitrate acquisition [18,19,20]. The transcription factor TCP20, which controls the nitrate foraging response [9,21], can also bind to promoters of type-A ARR5/7 , providing an additional link between nitrogen and cytokinin signalling [18,19].…”

“…Cytokinin also participates in nitrate foraging, which involves plants’ preferential development of lateral roots in nitrate-rich areas, thereby maximizing nitrate acquisition [18,19,20]. The transcription factor TCP20, which controls the nitrate foraging response [9,21], can also bind to promoters of type-A ARR5/7 , providing an additional link between nitrogen and cytokinin signalling [18,19]. Thus, the disruption of cytokinin signalling affects nitrate uptake, as demonstrated in the Arabidopsis cytokinin signalling mutant arr1,10,12 .…”

“…Recent findings also show that long-distance transport of the cytokinin precursor t ZR (which has low activity) can account for nitrate availability-mediated adjustments of shoot apical meristem size and organogenesis rates through modulating the expression of WUSCHEL [32]. Root-to-shoot cytokinin signalling operates in both directions, and, for example, lateral root growth is regulated by t Z content in the shoot [18,19,20]. …”

Inside out: root cortex‐localized LHK1 cytokinin receptor limits epidermal infection of Lotus japonicus roots by Mesorhizobium loti

“…The plant hormone cytokinin was shown to be important in this context. Cytokinins, long recognized as local and systemic messengers of soil N availability and the plant N status (Kiba & Krapp, 2016;Osugi et al, 2017;Landrein et al, 2018), were recently shown to mediate a shoot-to-root N demand signalling that shapes the plant responses to heterogeneous soil nitrate conditions (Ruffel et al, 2016;Poitout et al, 2018). Cytokinins are also known to locally and systemically regulate root nodule formation, hence aiding in the symbiotic N 2 acquisition (Cooper & Long, 1994;Murray et al, 2007;Frugier et al, 2008;Sasaki et al, 2014;Gamas et al, 2017;Reid et al, 2017).…”

HRS1/HHOs GARP transcription factors and reactive oxygen species are regulators of Arabidopsis nitrogen starvation response

“…Long-distance N-related root-shoot-root signals have also been shown to adapt plant development and metabolism to the whole nitrogen status of the plant (Gansel et al, 2001;Li et al, 2014;Ruffel et al, 2011;Ruffel et al, 2015). These long-distance signals can be divided into N-demand signals and N-supply signals, which can be genetically uncoupled Ruffel et al, 2011;Ruffel et al, 2015).…”