Inhibition of Aminotransferases by Aminoethoxyvinylglycine Triggers a Nitrogen Limitation Condition and Deregulation of Histidine Homeostasis That Impact Root and Shoot Development and Nitrate Uptake.

Erwan Le Deunff,Patrick Beauclair,Carole Deleu,Julien Lecourt

doi:10.3389/fpls.2019.01387

Abstract

Background and Aims: Although AVG (aminoethoxyvinylglycine) is intensely used to decipher signaling in ethylene/indol-3-acetic acid (IAA) interactions on root morphogenesis, AVG is not a specific inhibitor of aminocyclopropane-1-carboxylate synthase (ACS) and tryptophan aminotransferase (TAA) and tryptophan aminotransferase related (TAR) activities since it is able to inhibit several aminotransferases involved in N metabolism. Indeed, 1 mM glutamate (Glu) supply to the roots in plants treated with 10 μM AVG partially restores the root growth. Here, we highlight the changes induced by AVG and AVG + Glu treatments on the N metabolism impairment and root morphogenetic program. Methods: Root nitrate uptake induced by AVG and AVG + Glu treatments was measured by a differential labeling with 15NO3 - and 15Nglutamate. In parallel a profiling of amino acids (AA) was performed to decipher the impairment of AA metabolism. Key Results: 10 μM AVG treatment increases K15NO3 uptake and 15N translocation during root growth inhibition whereas 10 μM AVG + 1 mM 15Nglutamate treatment inhibits K15NO3 uptake and increases 15Nglutamate uptake during partial root growth restoration. This is explained by a nitrogen (N) limitation condition induced by AVG treatment and a N excess condition induced by AVG + Glu treatment. AA levels were mainly impaired by AVG treatment in roots, where levels of Ser, Thr, α-Ala, β-Ala, Val, Asn and His were significantly increased. His was the only amino acid for which no restoration was observed in roots and shoots after glutamate treatment suggesting important control of His homeostasis on aminotransferase network. Results were discussed in light of recent findings on the interconnection between His homeostasis and the general amino acid control system (GAAC) in eukaryotes. Conclusions: These results demonstrate that AVG concentration above 5 μM is a powerful pharmacological tool for unraveling the involvement of GAAC system or new N sensory system in morphological and metabolic changes of the roots in leguminous and non-leguminous plants.

Highlights

Inhibitors of aminotransferases such as aminoethoxyvinylglycine (AVG), Rhizobitoxine and aminooxyacetic acid (AOA) have recently been demonstrated to be non-specific, possessing a broad inhibitory spectrum (Berkowitz et al, 2006; Soeno et al, 2010; Le Deunff and Lecourt, 2016, Le Deunff, 2018)
Changes in the exploratory root system elongation and shoot surface area expansion in B. napus plantlets were examined on vertical agar plates under a homogeneous supply of 1 mM nitrate with different concentrations of AVG (0.5 to 20 μM) after 120 h of treatment (Figure 1)
The differential morphological effects measured between shoot and root raised the question: does AVG treatment induce a profound remodeling of N and C metabolism in the roots and shoots irrespective of the inhibition of ethylene and indol-3-acetic acid (IAA) biosynthesis?

Summary

Introduction

Inhibitors of aminotransferases such as aminoethoxyvinylglycine (AVG), Rhizobitoxine and aminooxyacetic acid (AOA) have recently been demonstrated to be non-specific, possessing a broad inhibitory spectrum (Berkowitz et al, 2006; Soeno et al, 2010; Le Deunff and Lecourt, 2016, Le Deunff, 2018) This offers the possibility to highlight the effects of nitrogen metabolism impairment on the root and shoot morphogenetic program and root nitrate uptake (Le Deunff and Lecourt, 2016; Le Deunff et al, 2016). Aminotransferases are the key enzymes involved in nitrogen (N), sulphur (S) and carbon (C) shuttling and distribution in plants through the interconversions between organic acids and amino acids (Christen and Mehta, 2001; Liepman and Olsen, 2004; Le Deunff, 2018) They catalyze amino group transfers from amino donor to amino acceptor. We highlight the changes induced by AVG and AVG + Glu treatments on the N metabolism impairment and root morphogenetic program

Methods

Results

Conclusion