Regulation of nitrate uptake and calcium signaling in arabidopsis
Nitrogen (N) is one of the key nutrients required by plants, and its most abundant form, nitrate (NO3-), has been extensively used in fertilizers to improve crop yield. However, this has also led to increased environmental pollution due to leaching and volatilization. Improving nitrogen use efficiency (NUE) is one of the ways to reduce this environmental impact. Nitrogen uptake efficiency (NUpE) is a key component of NUE. The first step in NO3- uptake is the sensing of NO3- signal which was captured through the use of fluorescence imaging. The calcium responses to NO3- as a signal were captured for the two uptake kinetic systems, high-affinity transporter system (HATS) and low-affinity transporter system (LATS). A unique calcium signature was identified in root epidermal cells and root hair cell-specific responses were captured in response to low NO3-. Two potential transcriptional regulators (TFs) were identified through gene regulatory network analysis of NO3--responsive time-series datasets, DIV1 and MYB28, which play an antagonistic role in regulating the expression of the NO3- transporters, NPF6.3 and NRT2.1, and few NO3- assimilation genes. Further characterization revealed the role of DIV1 and MYB28 in altering the functional NO3- transporter activity, highlighting their role as potential candidates for improving NUpE. The regulation of the transporters occurs at the levels of transcription and post-translation. These regulatory processes were captured through individual models, which were combined into an integrated multiscale model describing the NO3- uptake dynamics for NPF6.3. The integrated model confirmed the switch between the uptake kinetic systems, HATS and LATS, to occur at NO3- concentrations above 1 mM and the threshold without incorporating the regulatory aspects was much lower, close to 0.4 mM. Further, at lower external NO3- concentrations, < 0.5 mM, the total assimilated N was more than 50% of the total predicted internal cellular N when using HATS kinetics, compared to only 30% to 40% assimilation when employing LATS mode for NPF6.3. These findings validate the existing knowledge about the NO3- uptake dynamics and open up avenues to study the impact of perturbations in the regulatory mechanisms on NO3- uptake, leading to novel possibilities of improving NUpE.
nitrate transport, transcriptional regulation, gene regulatory networks, calcium signaling, mathematical modeling
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign