FQR1, a Novel Primary Auxin-Response Gene, Encodes a Flavin Mononucleotide-Binding Quinone Reductase

Abstract

(I.M.S.) FQR1 is a novel primary auxin-response gene that codes for a flavin mononucleotide-binding flavodoxin-like quinone reductase. Accumulation of FQR1 mRNA begins within 10 min of indole-3-acetic acid application and reaches a maximum of approximately 10-fold induction 30 min after treatment. This increase in FQR1 mRNA abundance is not diminished by the protein synthesis inhibitor cycloheximide, demonstrating that FQR1 is a primary auxin-response gene. Sequence analysis reveals that FQR1 belongs to a family of flavin mononucleotide-binding quinone reductases. Partially purified His-tagged FQR1 isolated from Escherichia coli catalyzes the transfer of electrons from NADH and NADPH to several substrates and exhibits in vitro quinone reductase activity. Overexpression of FQR1 in plants leads to increased levels of FQR1 protein and quinone reductase activity, indicating that FQR1 functions as a quinone reductase in vivo. In mammalian systems, glutathione S-transferases and quinone reductases are classified as phase II detoxification enzymes. We hypothesize that the auxin-inducible glutathione S-transferases and quinone reductases found in plants also act as detoxification enzymes, possibly to protect against auxin-induced oxidative stress.Auxin plays a central role in the control of plant growth and development. It can stimulate or inhibit cell expansion, stimulate cell division, promote differentiation of vascular tissues, inhibit shoot branching, and promote lateral root formation. Although recent attempts to unravel these signal transduction pathways have been quite successful, it is clear that we have not identified all of the genes that are upregulated immediately after auxin application.At present, about a half a dozen families of primary auxin-response genes have been identified. These include the Aux/IAA, SAUR, and GH3 families, members of gene families encoding glutathione S-transferases (GST) and 1-aminocyclopropane-1-carboxylic acid synthases, and NAC1 (for review, see Abel and Theologis, 1996;Xie et al., 2000). Of these, the Aux/IAA family is the most thoroughly studied (Abel et al., 1995). Aux/IAA genes are transcriptional regulators, and gain-of-function mutations in some family members have dramatic effects on plant development (Nagpal et al., 2000;Rogg et al., 2001). Transcription of the Aux/IAA genes is under the control of auxin-response elements (AuxREs; for review, see Guilfoyle et al., 1998).The GSTs are a distinct class of auxin-responsive genes (for review, see Marrs, 1996). This family of enzymes was named for its ability to conjugate compounds, including xenobiotic compounds, to the tripeptide glutathione. Once such a complex has formed, the glutathione serves as a tag, marking the complex for transport into the vacuole (for review, see Edwards et al., 2000). As a result of this activity, GSTs protect cells from potentially damaging agents.In mammalian systems, GSTs are classified as phase II detoxifying enzymes. Detoxification of xenobiotic and/or cancer-causing compounds often occu...

Auxin-Responsive Genes AIR12 Code for a New Family of Plasma Membrane b-Type Cytochromes Specific to Flowering Plants

“…Notably, only a few redox proteins known to interact with the PM are upregulated in Arabidopsis roots soon after auxin treatment and are implicated in lateral root emergence (Laskowski et al, 2006). These include AIR12, as well as flavodoxin-like quinone reductase (FQR1; Laskowski et al, 2002), multicopper oxidase SKU5, and a putative peroxidase (At5g64100), all of which could interact directly with AIR12 on the apoplastic side of the PM. SKU5, probably an ascorbate oxidase, is involved in directional growth of Arabidopsis roots (Sedbrook Figure 10.…”

A Single-Electron Reducing Quinone Oxidoreductase Is Necessary to Induce Haustorium Development in the Root Parasitic Plant Triphysaria

“…Transcription of xenobiotic metabolizing enzymes is often regulated by their substrates and has been observed in plants, animals, and fungi (Prestera and Talalay, 1995;Testa, 1995;Akileswaran et al, 1999;Laskowski et al, 2002;Greenshields et al, 2005). DT-diaphorase (menadione reductase activity) is induced in mammalian cells treated with a wide range of electrophilic chemical carcinogens (Cadenas et al, 1992).…”

FaQR, Required for the Biosynthesis of the Strawberry Flavor Compound 4-Hydroxy-2,5-Dimethyl-3(2H)-Furanone, Encodes an Enone Oxidoreductase

“…Incubation experiments with NADPH instead of NADH yielded ;80% of the amount of HDMF compared with NADH. Addition of Zn 2þ ions did not increase the enzymatic activity, and the UV spectrum of the enzymatically active recombinant enzyme did not show the typical maximum of flavin-containing proteins at 450 nm (Laskowski et al, 2002).…”

“…The NAD(P)H binding motif GXXGXXG is marked. (Laskowski et al, 2002) does not match the protein deduced sequence from the FaQR cDNA. Finally, using the National Center for Biotechnology Information Conserved Domain Search program, we compared the deduced FaQR protein with domains included in the database.…”