Perception of root-derived peptides by shoot LRR-RKs mediates systemic N-demand signaling

Abstract

Nitrogen (N) is a critical nutrient for plants but is often distributed unevenly in the soil. Plants therefore have evolved a systemic mechanism by which N starvation on one side of the root system leads to a compensatory and increased nitrate uptake on the other side. Here, we study the molecular systems that support perception of N and the long-distance signaling needed to alter root development. Rootlets starved of N secrete small peptides that are translocated to the shoot and received by two leucine-rich repeat receptor kinases (LRR-RKs). Arabidopsis plants deficient in this pathway show growth retardation accompanied with N-deficiency symptoms. Thus, signaling from the root to the shoot helps the plant adapt to fluctuations in local N availability.

Different Pathways Act Downstream of the CEP Peptide Receptor CRA2 to Regulate Lateral Root and Nodule Development

“…For instance, cepr1 phenotypes in Arabidopsis are somewhat different compared to cra2 phenotypes in M. truncatula (Tabata et al, 2014, Huault et al, 2014. In addition, the phenotypic effects of CEP peptides on lateral root and main root growth are different in Arabidopsis and Medicago (Delay et al, 2013;Imin et al, 2013;Tabata et al, 2014). Therefore, modulating CEP pathways may be a way to generate different root system architectures in various plants depending on their environments.…”

“…The cra2 phenotypes, therefore, are opposite to those observed by raising MtCEP1 levels . CRA2 is most closely related to the Arabidopsis (Arabidopsis thaliana) XYLEM INTERMIXED IN PHLOEM (XIP1)/CEP RECEPTOR1 (CEPR1) receptor (Bryan et al, 2012) that specifically binds CEP peptides (Tabata et al, 2014). This makes CRA2 a candidate receptor for MtCEP1 peptides.…”

“…Therefore, understanding signaling molecules, receptors, and downstream pathways that regulate both nodule and LR development in legumes under different environmental conditions is essential to improve nutrient acquisition by the root system. C-TERMINALLY ENCODED PEPTIDEs (CEPs) have recently been implicated in controlling major aspects of root development (Ohyama et al, 2008;Delay et al, 2013;Imin et al, 2013;Tabata et al, 2014;Djordjevic et al, 2015;Mohd-Radzman et al, 2015). CEP peptides are signaling molecules that positively regulate nodulation and negatively regulate LR emergence in several legumes Mohd-Radzman et al, 2015).…”

Signature motif-guided identification of receptors for peptide hormones essential for root meristem growth

“…Intriguingly, the RxR motif is largely conserved in this subfamily of LRR-RKs ( Figure 1B). Furthermore, several members of this LRR-RK subfamily have been shown to recognize small peptides ending with histidine or asparagine [20][21][22][23][24][25]. These findings prompted us to hypothesize that members of the LRR XI subfamily may act as receptors of small peptides with a free C-terminal histidine or asparagine.…”

RGF1 INSENSITIVE 1 to 5, a group of LRR receptor-like kinases, are essential for the perception of root meristem growth factor 1 in Arabidopsis thaliana

“…A pre-proprotein is cleaved by a peptidase in the endoplasmic reticulum to remove the N-terminal peptide sequence and subsequently forms a proprotein, which is then modified and packaged into membrane-bound secretory vesicles [3]. Specific endoproteases can then cleave the proprotein to form an active peptide hormone, which is secreted into apoplast and perceived by cell surface receptors such as leucine-rich repeat (LRR) receptor-like kinases (RLKs; LRR-RLKs) [4][5][6].…”