RUI: Defining the Connections between Nitrate-regulated Glutaredoxins and Root System Architecture

California State University San Marcos Corporation, San Marcos CA

Investigators

Abstract

Of the many soil mineral nutrients required for plant growth, nitrogen is required in the largest amounts and is most often limiting. The researchers previously showed that the most commonly available form of soil nitrogen, nitrate, activates a set of plant genes called glutaredoxins that act to slow the growth of the plant's main root. This response appears to be part of an adaptive program that allows plants to maximize nitrate uptake from the soil by slowing growth of the main root while increasing the growth of side roots when they encounter nitrate-rich soil patches. The researchers, who include students at California State University San Marcos (CSUSM), will characterize the molecular mechanisms that link glutaredoxins to primary root growth. This basic research on plant root systems has the potential to impact agriculture in the long term by improving understanding of the ways that root growth can be altered in response to environmental conditions. A better understanding of how glutaredoxins regulate root growth could have implications on agriculturally-important traits such as plant drought tolerance and nitrogen use efficiency. Previous research has shown that nitrate strongly activates the expression of a group of six genes encoding glutaredoxin enzymes in Arabidopsis thaliana. Higher plants possess a substantially larger number of glutaredoxins than other, yet plant glutaredoxins remain very poorly characterized. Functional characterization of the nitrate-regulated glutaredoxins demonstrated that they act as negative regulators of primary root growth, linking root system development to nitrate distribution and availability in the soil. The proposed research will elucidate the molecular mechanisms whereby the nitrate-induced glutaredoxins act to regulate the growth of the Arabidopsis primary root. To further explore the functions of nitrate-regulated glutaredoxins, a series of glutaredoxin mutants will be created using CRISPR/Cas9 technology. In addition, transcriptional and translational fusions will be used to characterize glutaredoxin expression domains and subcellular localization. Because the mechanistic links between root growth and glutaredoxins are unclear, glutaredoxin protein interaction partners will be identified using both targeted approaches (verifying putative interactions with TGA transcription factors) and non-targeted approaches (yeast two-hybrid analyses). Glutaredoxin-regulated gene expression networks will also be characterized by performing comparative transcriptomics on glutaredoxin mutant lines. Overall, this research will reveal the molecular underpinnings of a complex developmental "behavior" that is utilized by the plant root system to maximize utilization of nitrate, a limiting resource in the soil.