A new cyanogenic metabolite in Arabidopsis required for inducible pathogen defence

Abstract

SUMMARYThousands of putative biosynthetic genes in Arabidopsis thaliana have no known function, suggesting that there are numerous molecules contributing to plant fitness that have not yet been discovered1,2. Prime among these uncharacterized genes are cytochromes P450 upregulated in response to pathogens3,4. Starting with a single pathogen-induced P4505, CYP82C2, we used a combination of untargeted metabolomics and co-expression analysis to uncover the complete biosynthetic pathway to a previously unknown Arabidopsis metabolite, 4-hydroxyindole-3-carbonyl nitrile (4-OH-ICN), which harbors cyanogenic functionality that is unprecedented in plants and exceedingly rare in nature6,7. The aryl cyanohydrin intermediate in the 4-OH-ICN pathway reveals a latent capacity for cyanogenic glucoside biosynthesis8,9 in Arabidopsis. By expressing 4-OH-ICN biosynthetic enzymes in Saccharomyces cerevisiae and Nicotiana benthamiana, we reconstitute the complete pathway in vitro and in vivo and validate the functions of its enzymes. 4-OH-ICN pathway mutants show increased susceptibility to the bacterial pathogen Pseudomonas syringae, consistent with a role in inducible pathogen defense. Arabidopsis has been the preeminent model system10,11 for studying the role of small molecules in plant innate immunity12; our results uncover a new branch of indole metabolism distinct from the canonical camalexin pathway, and support a role for this pathway in the Arabidopsis defense response.13 These results establish a more complete framework for understanding how the model plant Arabidopsis uses small molecules in pathogen defense.

Plastic Transcriptomes Stabilize Immunity to Pathogen Diversity: The Jasmonic Acid and Salicylic Acid Networks within the Arabidopsis/Botrytis Pathosystem

“…While camalexin controls resistance to some B. cinerea isolates depending upon their genotype, little is known about how this phytoalexin may influence the interaction with a broad population of isolates (Kliebenstein et al, 2005;Bednarek et al, 2011;Rajniak et al, 2015;Frerigmann et al, 2016). Comparing the transcript accumulation for all the enzymes in the biochemical pathway and the final defense metabolite showed that while camalexin accumulation is highly diminished in the coi1-1 background, the transcriptional response of the genes encoding the biosynthetic enzyme is largely intact in this JA mutant ( Figure 4A; Supplemental Figure 1).…”

Glucosinolates from Host Plants Influence Growth of the Parasitic Plant Cuscuta gronovii and Its Susceptibility to Aphid Feeding

“…As noted above, camalexin and 4OH-ICN are phytoalexins that function against bacterial, fungal, and oomycete pathogens (Rogers et al, 1996;Glazebrook et al, 1997;Ferrari et al, 2007;Schlaeppi et al, 2010;Wang et al, 2013;Rajniak et al, 2015) and also vary in our Arabidopsis lines. Whether these metabolites also function in deterring parasitic plants is an open question.…”

“…As noted above, the mutants exhibiting contrasting effects on dodder growth, atr1D and cyp79B2/B3, have opposite effects on levels of indole-3-acetaldoxime, a key precursor for multiple indole metabolites that function in development and defense. Known downstream species include auxin, camalexin, indole-3-carbonyl nitrile, and indole glucosinolates (Zhao et al, 2002;Glawischnig et al, 2004;Celenza et al, 2005;Rajniak et al, 2015), each of which merits consideration for potential involvement in host-plant resistance to dodder, as discussed below.…”

Illuminating a plant’s tissue-specific metabolic diversity using computational metabolomics and information theory

“…Regulatory mechanisms coordinating these processes are only beginning to be uncovered for some model metabolic pathways such as the metabolic pathways of the family of glucosinolates in Brassicacae (9). Coexpression analysis using information about gene and secondary metabolite cross-tissue expression patterns has been applied successfully to infer biosynthetic genes in secondary metabolism (4,10,11). In Arabidopsis, several "-omics"-based tissue atlases (e.g., for gene expression, alternative splicing, proteome) are publicly accessible to conduct such types of analysis (12).…”