Mutations in the Arabidopsis ROL17/isopropylmalate synthase 1 locus alter amino acid content, modify the TOR network, and suppress the root hair cell development mutant lrx1.

Myriam Schaufelberger,Anouck Diet,Florian Galbier,Christoph Ringli,Stefan Roffler,Gilles Clement,Aline Herger,Stefan Hörtensteiner,Thomas Wicker,Rita De Brito Francisco

doi:10.1093/jxb/ery463

Abstract

The growth and development of organisms must be tightly controlled and adjusted to nutrient availability and metabolic activities. The Target of Rapamycin (TOR) network is a major control mechanism in eukaryotes and influences processes such as translation, mitochondrial activity, production of reactive oxygen species, and the cytoskeleton. In Arabidopsis thaliana, inhibition of the TOR kinase causes changes in cell wall architecture and suppression of phenotypic defects of the cell wall formation mutant lrx1 (leucine-rich repeat extensin 1). The rol17 (repressor of lrx1 17) mutant was identified as a new suppressor of lrx1 that induces also a short root phenotype. The ROL17 locus encodes isopropylmalate synthase 1, a protein involved in leucine biosynthesis. Dependent on growth conditions, mutations in ROL17 do not necessarily alter the level of leucine, but always cause development of the rol17 mutant phenotypes, suggesting that the mutation does not only influence leucine biosynthesis. Changes in the metabolome of rol17 mutants are also found in plants with inhibited TOR kinase activity. Furthermore, rol17 mutants show reduced sensitivity to the TOR kinase inhibitor AZD-8055, indicating a modified TOR network. Together, these data suggest that suppression of lrx1 by rol17 is the result of an alteration of the TOR network.

Highlights

Owing to their sessile nature, plants have a strong and development
Rol17 mutants show reduced sensitivity to the Target of Rapamycin (TOR) kinase inhibitor AZD-8055, indicating a modified TOR network. These data suggest that suppression of lrx1 by rol17 is the result of an alteration of the TOR network
Modulation of the activity of proteins involved in the TOR network frequently leads to an alteration in the sensitivity of the TOR network to TOR kinase inhibitors.This characteristic feature has been used in chemical genetic screens to identify components or processes that are functionally connected to the TOR network

Summary

Introduction

Owing to their sessile nature, plants have a strong and development. This optimization is not limited to the tarneed to monitor environmental conditions to optimize growth geted uptake of nutrients but includes adjusting metabolicAbbreviations: BCAA, branched-chain amino acid; EMS, ethyl methanesulfonate; GSL, glucosinolate; HG, Hoagland; IPMS1, isopropylmalate synthase 1; Leu, leucine; LRX, leucine-rich repeat extensin; MS, Murashige and Skoog; rol, repressor of lrx; TOR, Target of Rapamycin; Val, valine.2314 | Schaufelberger et al.activities to the available resources. Owing to their sessile nature, plants have a strong and development This optimization is not limited to the tarneed to monitor environmental conditions to optimize growth geted uptake of nutrients but includes adjusting metabolic. A TOR kinase-specific inhibitor, is instrumental in the characterization of the TOR network and is used in medical applications owing to its growth-inhibiting, antitumor, and immunosuppressive properties (Huang et al, 2003; Martelli et al, 2018). The development of a new generation of FKBP12independent, TOR-specific ATP-competitive active-site inhibitors such as AZD-8055 circumvents this problem and provides excellent tools for more direct analysis of the TOR network in plants by pharmaceutical means (Chresta et al, 2010; Liu et al, 2011; Montané and Menand, 2013; Dobrenel et al, 2016b; Schepetilnikov et al, 2017). The genes identified in this way have diverse functions including transcriptional regulation, amino acid metabolism, and tRNA maturation (Chan et al, 2000; Goehring et al, 2003; Li et al, 2015)

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