Abstract
Plant secondary metabolites and their biosynthesis have attracted great interest, but investigations of the activities of hidden intermediates remain rare. Gossypol and related sesquiterpenes are the major phytoalexins in cotton. Among the six biosynthetic intermediates recently identified, 8-hydroxy-7-keto-δ-cadinene (C234) crippled the plant disease resistance when accumulated upon gene silencing. C234 harbours an α,β-unsaturated carbonyl thus is a reactive electrophile species. Here, we show that C234 application also dampened the Arabidopsis resistance against the bacterial pathogen Pseudomonas syringae pv. maculicola (Psm). We treated Arabidopsis with C234, Psm and (Psm+C234), and analysed the leaf transcriptomes. While C234 alone exerted a mild effect, it greatly stimulated an over-response to the pathogen. Of the 7335 genes affected in the (Psm+C234)-treated leaves, 3476 were unresponsive without the chemical, in which such functional categories as ‘nucleotides transport’, ‘vesicle transport’, ‘MAP kinases’, ‘G-proteins’, ‘protein assembly and cofactor ligation’ and ‘light reaction’ were enriched, suggesting that C234 disturbed certain physiological processes and the protein complex assembly, leading to distorted defence response and decreased disease resistance. As C234 is efficiently metabolized by CYP71BE79, plants of cotton lineage have evolved a highly active enzyme to prevent the phytotoxic intermediate accumulation during gossypol pathway evolution.This article is part of the theme issue ‘Biotic signalling sheds light on smart pest management’.
Highlights
As sessile organisms, plants protect themselves from herbivores and pathogens by synthesizing structurally diversified secondary metabolites, many of which exert defence function by their cytotoxicity [1]
The cDNAs were synthesized from 2 mg RNAs by genomic DNA removal and cDNA synthesis kit (Transgene, Beijing), followed by amplification with gene-specific primers designed according to National Center for Biotechnology Information (NCBI) Primer-Blast
To test whether the influence of C234 on plant defence is general or specific to cotton, we examined its activity on Arabidopsis
Summary
Plants protect themselves from herbivores and pathogens by synthesizing structurally diversified secondary (specialized) metabolites, many of which exert defence function by their cytotoxicity [1]. In cotton plants gossypol and related sesquiterpene aldehydes are the major phytoalexins against pathogens and pests They are generally toxic [9,10] and stored in pigmented glands of aerial organs and in epidermal layers of roots [6]. To determine the proportions of the C234 and Psm responsive genes in gene families (http://www.arabidopsis.org/), MAPMAN categories and the respective gene sets were aligned to the RNA-seq datasets using Microsoft EXCEL [18]. The cDNAs were synthesized from 2 mg RNAs by genomic DNA removal and cDNA synthesis kit (Transgene, Beijing), followed by amplification with gene-specific primers designed according to National Center for Biotechnology Information (NCBI) Primer-Blast (www.ncbi.nlm.nih.gov/tools/primer-blast/). The sequencing data have been deposited in the NCBI (https:// www.ncbi.nlm.nih.gov/) under the accession numbers of SRR7686004– SRR7686015
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