Conserved and unique functions of NIN-like proteins in nitrate sensing and signaling

Nitrogen is the most abundant element in the atmosphere and serves as the foundation block of life, including plants on earth. Unlike carbon fixation through photosynthesis, plants rely heavily on external supports to acquire nitrogen. To this end, plants have adapted various strategies such as forming mutualistic relationships with nitrogen-fixing bacteria and evolving a large regulatory network that includes multiple transporters, sensors, and transcription factors for fine-tuning nitrate sensing and signaling. Nodule Inception (NIN) and NIN-like protein (NLP) are central in this network by executing multiple functions such as initiating and regulating the nodule symbiosis for nitrogen fixation, acting as the intracellular sensor to monitor the nitrate fluctuations in the environment, and activating the transcription of nitrate-responsive genes for optimal nitrogen uptake, assimilation, and usage. The involvement of NLPs in intracellular nitrate binding and early nitrate responses highlight their pivotal role in the primary nitrate response (PNR). Genome-wide reprogramming in response to nitrate by NLP is highly transient and rapid, requiring regulation in a precise and dynamic manner. This review aims to summarize recent progress in the study of NIN/NLP for a better understanding of the molecular basis of their roles and regulations in nitrate sensing and signaling, with the hope of shedding light on increasing biological nitrogen fixation and improving nitrogen use efficiency (NUE) to minimize fertilizer input in agriculture.

Au-modified organic/inorganic MWCNT/Cu/PANI hybrid nanocomposite electrode for electrochemical determination of nitrate ions

A new electrochemical sensor is reported for the based on the application of noble bimetal nanoparticles (gold and copper) to polymeric-carbon-modifiers for the reduction of nitrate. This sensor was designed for nitrate ion measurement at the surface of pencil graphite electrode modified by a nanocomposite. The modification was the electrosynthesis of gold nanoparticles on the MWCNT/copper-polyaniline (Cu-PANI) nanocomposite. Physicochemical properties of the synthesized hybrid nanocomposites and their surface performance efficiency are characterized using microscopic, spectroscopic, and electrochemical techniques. At optimized pH, the nitrate peak current (at working potential of 1084 mV versus Ag/AgCl reference electrode) was linear in the concentration range 0.8-30.0 μM with a detection limit of 0.09 μM using differential pulse voltammetry. Modified sensor was successfully implemented to quantify nitrate ions in wastewater resulting from the production line for industrial barium chromate and an example of aqueduct water with appropriate recovery levels. • Aniline was polymerized in phosphoric acid solution using peroxydisulfate as an initiator. • MWCNT@CuNPs@PANNSs@AuNPs nanocomposite on PGE electrode was revealed specific recognition for NO₃^-. • The electrochemical sensor displayed high selectivity and sensitivity for the detection of NO₃^-.