Signaling Responses to N Starvation: Focusing on Wheat and Filling the Putative Gaps With Findings Obtained in Other Plants. A Review

Abstract

Wheat is one of the most important food crops worldwide. In recent decades, fertilizers, especially nitrogen (N), have been increasingly utilized to maximize wheat productivity. However, a large proportion of N is not used by plants and is in fact lost into the environment and causes serious environmental pollution. Therefore, achieving a low N optimum via efficient physiological and biochemical processes in wheat grown under low-N conditions is highly important for agricultural sustainability. Although N stress-related N capture in wheat has become a heavily researched subject, how this plant adapts and responds to N starvation has not been fully elucidated. This review summarizes the current knowledge on the signaling mechanisms activated in wheat plants in response to N starvation. Furthermore, we filled the putative gaps on this subject with findings obtained in other plants, primarily rice, maize, and Arabidopsis. Phytohormones have been determined to play essential roles in sensing environmental N starvation and transducing this signal into an adjustment of N transporters and phenotypic adaptation. The critical roles played by protein kinases and critical kinases and phosphatases, such as MAPK and PP2C, as well as the multifaceted functions of transcription factors, such as NF-Y, MYB, DOF, and WRKY, in regulating the expression levels of their target genes (proteins) for low-N tolerance are also discussed. Optimization of root system architecture (RSA) via root branching and thinning, improvement of N acquisition and assimilation, and fine-tuned autophagy are pivotal strategies by which plants respond to N starvation. In light of these findings, we attempted to construct regulatory networks for RSA modification and N uptake, transport, assimilation, and remobilization.

Metabolome and RNA-seq Analysis of Responses to Nitrogen Deprivation and Resupply in Tea Plant (Camellia sinensis) Roots

“…Simultaneously, N-related transporters like AMT, are active and reduce NH 4 + efflux, and TFs like MYB (Zhang et al, 2021) may also take effects. Collectively, the slight increase of theanine content may be attributed to the cooperation of the entire regulatory network in response to N deprivation in C. sinensis roots (Kong et al, 2021). Tea polyphenols and catechins are important components of C pool in tea plant.…”

“…Various transporters, TFs, and genes related to N/AAs metabolism and hormone were involved in the response to N stress. Transporters and genes involved in N/AAs metabolism help to promote N/AAs metabolism and maintain the normal transport and N cycle (Kong et al, 2021). TFs are also essential for secondary metabolism as well as stress tolerance.…”

“…The most important regulators in the root N absorption system include signal transduction, transcription factors (TFs), plant hormones, N-related enzymes, and transporters, etc. (Kong et al, 2021). reported a novel Ca 2+ signaling triggered by nitrate called nitrate-Ca 2+ -sensor protein kinases (CPK)-Nin-Like Protein (NLP), which is considered to be the center of plant nutrient-growth regulatory network in Arabidopsis leaves and roots.…”

The use of ecological analytical tools as an unconventional approach for untargeted metabolomics data analysis: the case of Cecropia obtusifolia and its adaptive responses to nitrate starvation

“…These effects are capable of increasing nitrogen input levels, reducing toxic ions (ROS), and promoting ion homeostasis, thus enhancing the activity of enzymes such as glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), nitrate reductase (NR), and nitrite reductase (NiR). The last two enzymes are closely associated with nitric oxide (NO), a small gas molecule related to redox that has an essential effect on seed germination, senescence, adventitious root development, and stomatal closure, making NO an essential molecule in plant responses to abiotic stress (Anwar et al 2018 ; Jia et al 2020 ; Jia et al 2021 ; Kong et al 2021 ; Kothari and Lachowiec 2021 ).…”

Differential metabolic rearrangements in the roots and leaves of Cicer arietinum caused by single or double nitrate and/or phosphate deficiencies

“…Another interpretation for the decreased leaf‐TSP level under NO 3 − starvation could be the increase of protein degradation, which might be accompanied by the export of obtained AAs from leaves to roots (Krapp et al., 2011). Therefore, N remobilization through the transport of AAs from the shoot to the growing roots could be an adaptive strategy against NO 3 − starvation (Kong et al., 2021; Krapp et al., 2011). This result is in accordance with previous studies on maize ( Zea mays ; Schluter et al., 2013; Schlüter et al., 2012) and Arabidopsis thaliana (Krapp et al., 2011).…”