Abstract
Among all essential mineral elements, nitrogen (N) is required in the largest amounts and thus is often a limiting factor for plant growth. N is taken up by plant roots in the form of water-soluble nitrate, ammonium, and, depending on abundance, low-molecular weight organic N. In soils, the availability and composition of these N forms can vary over space and time, which exposes roots to various local N signals that regulate root system architecture in combination with systemic signals reflecting the N nutritional status of the shoot. Uncovering the molecular mechanisms underlying N-dependent signaling provides great potential to optimize root system architecture for the sake of higher N uptake efficiency in crop breeding. In this review, we summarize prominent signaling mechanisms and their underlying molecular players that derive from external N forms or the internal N nutritional status and modulate root development including root hair formation and gravitropism. We also compare the current state of knowledge of these pathways between Arabidopsis and graminaceous plant species.
Highlights
As a major constituent of biomolecules, nitrogen (N) has a strong impact on plant growth and development, in both natural and agricultural ecosystems
Under persistent N deficiency, early lateral root development is modulated by a regulatory pathway that involves CLAVATA3/ ESR-related (CLE) signaling peptides and their receptor protein, the leucine-rich repeat (LRR) receptor-like kinase CLAVATA1 (CLV1) (Araya et al, 2014a, b, 2016).While expression of several CLE homologs, including CLE3, is up-regulated by low N (≤0.1 mM) in pericycle cells, the receptor protein CLV1 localizes to phloem companion cells (Araya et al, 2014a)
Over the past couple of years, several root responses to N have been investigated across plant species and found to be highly conserved.Significant progress has been made in elucidating the molecular and cellular basis of how roots sense environmental N signals, in particular by the discovery of phytohormones and peptides conveying local and systemic N signals in the model plant Arabidopsis (Tabata et al, 2014; Ohkubo et al, 2017; Poitout et al, 2018; Jia et al, 2019a)
Summary
As a major constituent of biomolecules, nitrogen (N) has a strong impact on plant growth and development, in both natural and agricultural ecosystems. It remains elusive whether the CEP signaling pathway regulates lateral root elongation in response to local NO3–. Genetic studies using abscisic acid (ABA) biosynthesis and signaling mutants suggested that ABA participates in the lateral root elongation response to local NO3– (Signora et al, 2001).
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