Signalling mechanisms underlying the morphological responses of the root system to nitrogen in Arabidopsis thaliana

Abstract

Plants display considerable developmental plasticity in response to changing environmental conditions. The adaptations of the root system to variations in N supply are an excellent example of such developmental plasticity. In Arabidopsis, four morphological adaptations to the N supply have been characterized: (i) a localized stimulatory effect of external nitrate on lateral root elongation; (ii) a systemic inhibitory effect of high tissue nitrate concentrations on the activation of lateral root meristems; (iii) a suppression of lateral root initiation by high C:N ratios, and (iv) an inhibition of primary root growth and stimulation of root branching by external L-glutamate. These responses have provided valuable experimental systems for the study of N signalling in plants. This article will highlight some recent progress made in this direction from studies using the Arabidopsis root system. One recent development of note has been the emerging evidence of a regulatory role of nitrate transporters in some of the responses. It has been reported that the AtNRT1.1 (CHL1) dual-affinity nitrate transporter acts upstream of the ANR1 MADS box gene in mediating the stimulatory effect of a localized nitrate supply on lateral root proliferation. The AtNRT2.1 high-affinity nitrate transporter seems to be involved in the repression of lateral root initiation by high C:N ratios. The systemic inhibitory effect of high nitrate supply on lateral root development, which is mediated by abscisic acid (ABA), may be linked to the recently identified ABA receptor, FCA. The newly discovered root architectural response to external L-glutamate potentially offers a valuable experimental tool for studying the biological function of plant glutamate receptors and amino acid signalling.

Kin recognition is a nutrient-dependent inducible phenomenon

“…3). 24,25 Furthermore, exudates collected from seedlings grown at 0.10xMS, rather than 1xMS, are more effective at inducing lateral root formation (Fig. 4).…”

“…[22][23][24] Nitrogen and phosphorus deficiencies, for example, are well established modulators of lateral root development. 24,25 Nutrient availability also alters exudate production and composition with the potential to impact both interorganismal interactions as well as nutrient uptake. [26][27][28][29] For example, in Sorghum bicolor reduced nitrogen and phosphorus levels promote the release of 5-deoxystrigol which encourages the recruitment of mycorrhizal fungi.…”

“…[22][23][24][25][26][27][28][29] Based on these prior observations we hypothesized that A. thaliana may utilize information regarding nutrient availability to influence decisions regarding competition based on neighbor identity. In other words, nutrient availability may influence the production of specific exudates associated with KR which could alter the RSA accordingly.…”

Nitrate transporters: an overview in legumes

“…For example, hormones coordinate the responses modulated by external environment, regulating both primary root growth and LR initiation and development. Auxin (indole-3-acetic acid, IAA) and ABA have both been proposed to play a role in mediating nitrate effects on LR development (Signora et al 2001;De Smet et al 2006;Walch-Liu et al 2006;Zhang et al 2007). In M. truncatula, studies (summarized on Fig.…”

Natural Variation of Root Traits: From Development to Nutrient Uptake

“…Because of the significance of nitrogen in survival and growth, plants have evolved many different mechanisms to adjust to various levels of nitrogen availability (Zhang et al, 2007). Four morphological responses to different nitrogen levels have been described in the Arabidopsis root (Zhang et al, 2007), indicating a high level of root developmental plasticity relating to nitrogen availability (Nibau et al, 2008).…”