CYP83B1, a Cytochrome P450 at the Metabolic Branch Point in Auxin and Indole Glucosinolate Biosynthesis in Arabidopsis

Abstract

Auxins are growth regulators involved in virtually all aspects of plant development. However, little is known about how plants synthesize these essential compounds. We propose that the level of indole-3-acetic acid is regulated by the flux of indole-3-acetaldoxime through a cytochrome P450, CYP83B1, to the glucosinolate pathway. A T-DNA insertion in the CYP83B1 gene leads to plants with a phenotype that suggests severe auxin overproduction, whereas CYP83B1 overexpression leads to loss of apical dominance typical of auxin deficit. CYP83B1 N-hydroxylates indole-3-acetaldoxime to the corresponding aci -nitro compound, 1-aci -nitro-2-indolyl-ethane, with a K m of 3 M and a turnover number of 53 min Ϫ 1 . The aci -nitro compound formed reacts non-enzymatically with thiol compounds to produce an N -alkyl-thiohydroximate adduct, the committed precursor of glucosinolates. Thus, indole-3-acetaldoxime is the metabolic branch point between the primary auxin indole-3-acetic acid and indole glucosinolate biosynthesis in Arabidopsis. INTRODUCTIONApical dominance, cell expansion, vascular differentiation, lateral root and root hair formation, phototropism, and root gravitropism are among the many processes in plants controlled by auxins (Davies, 1995). The level of auxin is regulated by both de novo biosynthesis and reversible and irreversible conjugation to sugars, amino acids, and peptides as well as by degradation. Although the chemical structure of the primary auxin, indole-3-acetic acid (IAA), has been known since the 1930s (Wildman, 1997), not much is known about how plants actually synthesize this essential compound. Plants appear to be capable of synthesizing IAA by both tryptophan-dependent and tryptophan-independent pathways. Classical incorporation studies with radiolabeled compounds have not unambiguously identified the precursors or elucidated the biosynthetic pathway for IAA. (For a recent review of IAA metabolism, see Normanly and Bartel [1999].)Although a number of mutants in IAA metabolic pathways and perception have been described, the genes involved and their biochemical function and physiological relevance have not all been elucidated (reviewed in Bartel, 1997;Normanly and Bartel, 1999). For example, both the rty/sur1/hls3/alf1 (Boerjan et al., 1995;Celenza et al., 1995;King et al., 1995;Lehman et al., 1996) and sur2 mutants are known to accumulate increased levels of free auxin. Identification of the gene products affected and elucidation of the biochemical roles of these proteins should increase our limited knowledge of IAA biosynthesis and regulation.A link between indole glucosinolates and auxin has often been suggested in the literature. Glucosinolates are sulfurcontaining bioactive natural products derived from amino acids and sequestered in vacuoles of cruciferous plants (Halkier, 1999). It has recently been shown that the cytochromes CYP79B2 and CYP79B3 of Arabidopsis metabolize tryptophan to indole-3-acetaldoxime. This metabolite is often suggested to be the precursor of indole-3-acetonitrile (IAN...

Mechanisms and ecological implications of plant‐mediated interactions between belowground and aboveground insect herbivores

“…Auxins have been shown to be translocated from AG to BG plant parts where they regulate root growth and BG plant defenses (Shi et al 2006;Benjamins and Scheres 2008). The biosynthesis of the auxin indole-3-acetic acid (IAA) is closely connected to that of indole glucosinolates, providing a direct link between the two metabolic pathways, those of phytohormones and plant defensive compounds in Brassicaceae (Bak et al 2001;RadojcˇicŔ edovnikovic´et al 2008). Changes in CKs levels and CKs-regulated gene expression in response to herbivory have been found not only locally but also systemically (Scha¨fer et al 2015).…”

Inference of Longevity-Related Genes from a Robust Coexpression Network of Seed Maturation Identifies Regulators Linking Seed Storability to Biotic Defense-Related Pathways

“…Further analysis of the genes with cis-regulatory ARF elements points to a role of the degradation of Trp upstream of the indole-3-acetic acid (IAA) and indole glucosinolate biosynthetic pathways (Supplemental Data Set 6). Four nodes in the longevity module are linked to this degradation pathway: CYP79B2, which converts Trp to indo-3-acetaldoxime, a precursor of both IAA and indole glucosinolates (Kim et al, 2015); CYP83B1 (SUPERROOT2 [SUR2]), an enzyme in the metabolic branch point between IAA and indole glucosinolate biosynthesis, regulating IAA homeostasis (Bak et al, 2001); CYP76C7, involved both in the Trp catabolic process and regulating CYP79B2 and SUR2; and CYP82C2, shown to modulate indole glucosinolate biosynthesis as well as jasmonate-induced root growth inhibition and defense gene expression (Liu et al, 2010).…”

The Arabidopsis Thylakoid ADP/ATP Carrier TAAC Has an Additional Role in Supplying Plastidic Phosphoadenosine 5′-Phosphosulfate to the Cytosol

“…In search for such a plastidic PAPS exporter in Arabidopsis, we searched publically available transcriptome profiles for genes coexpressed with genes associated with GS biosynthesis (ATTED, www. atted.jp), such as CYP79B2, CYP83B1, SUR1, UGT74B1, and MYB122 (Mikkelsen et al, 2000(Mikkelsen et al, , 2004Bak et al, 2001;Naur et al, 2003;Gigolashvili et al, 2007a;Malitsky et al, 2008). Additionally, we searched for putative transporters among genes upregulated in the Arabidopsis apk1 apk2 mutant as almost all genes of the GS biosynthetic network were induced in this mutant .…”