Adaptive Regulation of Nitrate Transceptor NRT1.1 in Fluctuating Soil Nitrate Conditions

Abstract

SummaryPlant adaptation in variable soil nitrate concentrations involves sophisticated signaling and transport systems that modulate a variety of physiological and developmental responses. However, we know very little about their molecular mechanisms. It has recently been reported that many of these responses are regulated by a transceptor NRT1.1, a transporter cum receptor of nitrate signaling. NRT1.1 displays dual-affinity modes of nitrate binding and establishes phosphorylated/non-phosphorylated states at the amino acid residue threonine 101 in response to fluctuating nitrate concentrations. Here we report that intrinsic structural asymmetries between the protomers of the homodimer NRT1.1 provide a functional basis for having dual-affinity modes of nitrate binding and play a pivotal role for the phosphorylation switch. Nitrate-triggered local conformational changes facilitate allosteric communications between the nitrate binding and the phosphorylation site in one protomer, but such communications are impeded in the other. Structural analysis therefore suggests the functional relevance of NRT1.1 interprotomer asymmetries.

Combined Allosteric Responses Explain the Bifurcation in Non-Linear Dynamics of 15N Root Fluxes Under Nutritional Steady-State Conditions for Nitrate

“…Moreover, it is clear from NPF6.3/NRT1.1 crystallization studies that the dimerization is responsible for the increase in nitrate uptake capacity after conformational change ( Sun et al., 2014 ; Parker and Newstead, 2014 ). A recent study demonstrated that intrinsic structural asymmetry between the protomers of the heterodimer NPF6.3/NRT1.1 explains the allosteric functioning of the transporter by local conformational changes caused by nitrate binding on one or two protomers ( Rashid et al., 2018 ). Therefore, our results confirm and demonstrate in vivo the involvement of the two nitrate binding sites required for the allosteric property of the NPF6.3/NRT1.1 transporter that is consistent with a progressive increase in proportions of dimeric versus monomeric proteins in the plasma membrane and the bifurcation in transport and translocation capacities of NPF6.3/NRT1.1 in response to high nitrate availability.…”

“…This mechanism is consistent with abrupt and high increase in xylem nitrate concentrations (<35 mM) observed experimentally during the night and under low transpiring conditions ( Herdel et al., 2001 ; Orieux et al., 2019 ) but also the presence of a potential binding site on the channel exposed to the apoplast. Although no link has been yet established between the X-QUAC and the NPF/NRT transporters such NPF6.3/NRT1.1 , the allosteric dependence of nitrate on the NPF6.3 transporter is intriguingly similar to the positive feedback regulation of X-QUAC exerted by the xylemic nitrate concentration ( Köhler and Raschke, 2007 ; Rashid et al., 2018 ). Therefore, the combined cooperative properties of nitrate transporter activities at both ends of symplastic pathway could consistently work for both the absorption and translocation of nitrate.…”

LeNRT1.1 Improves Nitrate Uptake in Grafted Tomato Plants under High Nitrogen Demand

“…Both transporters, LeNRT1.1 and LeNRT1.2 , act as symporters coupled to the uptake of H + into the roots [7]. However, LeNRT1.1 presents the capacity to absorb NO 3 − in a wide range of external concentrations due to its ability to modify the protein structural flexibility by phosphorylation/dephosphorylation [15,16]. The only report available in tomatoes, showing no modification in the expression of LeNRT1.1 under different growth conditions, relates this response to the colonization by mycorrhiza; the expression of LeNRT2.3 is affected instead [17].…”

Allosteric regulation of glutamate dehydrogenase deamination activity

“…Protein structure was prepared for point mutation using Chimera rotamers tool (In structure editing section) 29 , 49 . Upon mutation, residue conformation was chosen according to highest probability from the rotamer library (probability is taken from the library that was not affect the structural environment but changed in Phi and Psi angle when Dunbrack library was used).…”