Aldoxime Metabolism Is Linked to Phenylpropanoid Production in Camelina sativa

Abstract

Plants produce diverse secondary metabolites. Although each metabolite is made through its respective biosynthetic pathway, plants coordinate multiple biosynthetic pathways simultaneously. One example is an interaction between glucosinolate and phenylpropanoid pathways in Arabidopsis thaliana. Glucosinolates are defense compounds made primarily from methionine and tryptophan, while phenylpropanoids are made from phenylalanine. Recent studies have shown that the accumulation of glucosinolate intermediate such as indole-3-acetaldoxime (IAOx) or its derivatives represses phenylpropanoid production via the degradation of phenylalanine ammonia lyase (PAL) functioning at the entry point of the phenylpropanoid pathway. Given that IAOx is a precursor of other bioactive compounds other than glucosinolates and that the phenylpropanoid pathway is present in most plants, we hypothesized that this interaction is relevant to other species. Camelina sativa is an oil crop and produces camalexin from IAOx. We enhanced IAOx production in Camelina by overexpressing Arabidopsis CYP79B2 which encodes an IAOx-producing enzyme. The overexpression of AtCYP79B2 results in increased auxin content and its associated morphological phenotypes in Camelina but indole glucosinolates were not detected in Camelina wild type as well as the overexpression lines. However, phenylpropanoid contents were reduced in AtCYP79B2 overexpression lines suggesting a link between aldoxime metabolism and phenylpropanoid production. Interestingly, the expression of PALs was not affected in the overexpression lines although PAL activity was reduced. To test if PAL degradation is involved in the crosstalk, we identified F-box genes functioning in PAL degradation through a phylogenetic study. A total of 459 transcript models encoding kelch-motifs were identified from the Camelina sativa database. Among them, the expression of CsKFBs involved in PAL degradation is up-regulated in the transgenic lines. Our results suggest a link between aldoxime metabolism and phenylpropanoid production in Camelina and that the molecular mechanism behind the crosstalk is conserved in Arabidopsis and Camelina.

Aldoximes are precursors of auxins in Arabidopsis and maize

“…We verified that all four KFBs that functioned redundantly in PAL degradation were upregulated in both ox‐1/WT and ox‐2/WT in a manner similar to IAOx‐based or aliphatic aldoxime‐based induction (Fig. 5e) (Kim et al, 2020; Zhang et al, 2020). This suggested that IAOx and PAOx shared all three of the known outcomes of aldoxime metabolism in Brassicales species: production of defence compounds, auxin biosynthesis and repression of the phenylpropanoid pathway (Fig.…”

“…The 35S:AtCYP79A2 and 35S:ZmCYP79A61 constructs were introduced into wild‐type (Col‐0), or ref2‐1 plants via Agrobacterium tumefaciens (GV3101)‐mediated transformation by following a method shown in Zhang et al . (2020). More than 10 T1 plants were screened by application of 0.2% Basta (Rely 280; BASF, NJ, USA).…”

“…Total RNA was extracted from whole aerial parts of 2-wk-old plants unless otherwise specified using the TRIzol method as per the manufacturer's protocol (15596026; Thermo Fisher Scientific). DNase treatment, cDNA synthesis and qRT-PCR analysis were conducted by following a method shown in a previous report (Zhang et al, 2020). 750 ng RNA was used for first-strand cDNA synthesis using reverse transcription kit (4368814; Thermo Fisher Scientific) and qPCR reactions were performed in a 10 µl volume mix using SYBR Green components (A25742; Thermo Fisher Scientific).…”

“…In Arabidopsis, tryptophan is converted to IAOx by the action of two redundant cytochrome P450 monooxygenases, CYP79B2 (At4g39950) and CYP79B3 (At5g05260) (Zhao, 2002). CYP79B2 overexpression lines in Arabidopsis and Camelina sativa contain increased levels of IAA, whereas cyp79b2 cyp79b3 double mutants (from this point forwards called b2b3 ) are deficient in high‐temperature‐dependent IAA production (Zhao, 2002; Zhang et al, 2020). Furthermore, IAOx consumption mutants such as ref5 and sur1 accumulate IAA due to the redirection of IAOx to IAA (Mikkelsen et al, 2004; Kim et al, 2015).…”

“…IAOx metabolism impacts plant growth not only via IAOxderived IAA production, but also through modulating phenylpropanoid metabolism (Kim et al, 2015(Kim et al, , 2020. The accumulation of IAOx or its derivatives increased the degradation of phenylalanine ammonia lyase (PAL), the entry point to the phenylpropanoid pathway in Arabidopsis and other Brassicales plants such as Camelina sativa (Kim et al, 2020;Zhang et al, 2020).…”