Nitrate-Regulated Glutaredoxins Control Arabidopsis Primary Root Growth

Abstract

Nitrogen is an essential soil nutrient for plants, and lack of nitrogen commonly limits plant growth. Soil nitrogen is typically available to plants in two inorganic forms: nitrate and ammonium. To better understand how nitrate and ammonium differentially affect plant metabolism and development, we performed transcriptional profiling of the shoots of ammoniumsupplied and nitrate-supplied Arabidopsis (Arabidopsis thaliana) plants. Seven genes encoding class III glutaredoxins were found to be strongly and specifically induced by nitrate. RNA silencing of four of these glutaredoxin genes (AtGRXS3/4/5/8) resulted in plants with increased primary root length (approximately 25% longer than the wild type) and decreased sensitivity to nitratemediated inhibition of primary root growth. Increased primary root growth is also a well-characterized phenotype of many cytokinin-deficient plant lines. We determined that nitrate induction of glutaredoxin gene expression was dependent upon cytokinin signaling and that cytokinins could activate glutaredoxin gene expression independent of plant nitrate status. In addition, crosses between "long-root" cytokinin-deficient plants and "long-root" glutaredoxin-silenced plants generated hybrids that displayed no further increase in primary root length (i.e. epistasis). Collectively, these findings suggest that AtGRXS3/4/5/8 operate downstream of cytokinins in a signal transduction pathway that negatively regulates plant primary root growth in response to nitrate. This pathway could allow Arabidopsis to actively discriminate between different nitrogen sources in the soil, with the preferred nitrogen source, nitrate, acting to suppress primary root growth (vertical dimension) in concert with its well-characterized stimulatory effect on lateral root growth (horizontal dimension).

The ALBA RNA-binding proteins function redundantly to promote growth and flowering in Arabidopsis

“…Also three members of the ROXY family (also known as GRX5, GRX8 and GRX11 ), are all downregulated. They are involved in cell redox homeostasis, and are all induced by nitrate (Patterson et al, 2016). Conversely, three members of the FE-UPTAKE-INDUCING PEPTIDE family, IRONMAN 1, IRONMAN 2 and IRONMAN 3 , were upregulated.…”

Arabidopsis γ‐glutamylcyclotransferase affects glutathione content and root system architecture during sulfur starvation

“…+S has the opposite effect. A similar RSA pattern has been observed for Arabidopsis nitrogen (N) nutrition (Patterson et al ., ) where it has been interpreted as a nutrient foraging mechanism that permits seedlings to probe deeper soil layers where nitrate accumulates (Gruber et al ., ). Plant response to sulfate is predicted to be similar to nitrate because both anions are highly soluble and settle deeper in soil (Gruber et al ., ).…”

“…In this regard it is important to note a recent study by Patterson et al . () who identified glutaredoxins (GRXs) that regulate RSA response to N‐limitation. GRXs are redox‐active proteins that were first characterized as using GSH as a reductant.…”

Molecular analysis of somatic embryogenesis through proteomic approach and optimization of protocol in recalcitrant Musa spp.

“…Two forms of GRX (spots 13 and 55), electron transfer flavoprotein subunit beta protein (spot 33) and UPF0235 protein C15orf40 homolog isoform X3 (spot 39) were expressed uniquely in germinating somatic embryos. GRX are known to be involved in plant responses to growth regulators like auxin, cytokinin and GA, which are necessary for growth and development of root and shoots (Eckardt , Kereamy et al , Patterson et al ). Kereamy et al () reported that the overexpression of GRX results in increased biosynthesis of GA and cytokinin, leading to the formation of shoots in rice whereas Patterson et al () reported that class 3 GRX plays a significant role in the root hormone regulation in Arabidopsis thaliana .…”