Abstract
BackgroundCruciferous plants synthesize a large variety of tryptophan-derived phytoalexins in response to pathogen infection, UV irradiation, or high dosages of heavy metals. The major phytoalexins of Eutrema salsugineum (Thellungiella salsuginea), which has recently been established as an extremophile model plant, are probably derivatives of indole glucosinolates, in contrast to Arabidopsis, which synthesizes characteristic camalexin from the glucosinolate precursor indole-3-acetaldoxime.ResultsThe transcriptional response of E. salsugineum to UV irradiation and AgNO3 was monitored by RNAseq and microarray analysis. Most transcripts (respectively 70% and 78%) were significantly differentially regulated and a large overlap between the two treatments was observed (54% of total). While core genes of the biosynthesis of aliphatic glucosinolates were repressed, tryptophan and indole glucosinolate biosynthetic genes, as well as defence-related WRKY transcription factors, were consistently upregulated. The putative Eutrema WRKY33 ortholog was functionally tested and shown to complement camalexin deficiency in Atwrky33 mutant.ConclusionsIn E. salsugineum, UV irradiation or heavy metal application resulted in substantial transcriptional reprogramming. Consistently induced genes of indole glucosinolate biosynthesis and modification will serve as candidate genes for the biosynthesis of Eutrema-specific phytoalexins.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0506-5) contains supplementary material, which is available to authorized users.
Highlights
Cruciferous plants synthesize a large variety of tryptophan-derived phytoalexins in response to pathogen infection, UV irradiation, or high dosages of heavy metals
We show that genes of tryptophan and indole glucosinolate biosynthesis and modification are highly upregulated providing candidates for phytoalexin biosynthesis
We investigated whether EsWRKY33 can functionally replace AtWRKY33 as a positive regulator of camalexin biosynthesis and expressed EsWRKY33 in the Arabidopsis wrky33-1 mutant [54]
Summary
Cruciferous plants synthesize a large variety of tryptophan-derived phytoalexins in response to pathogen infection, UV irradiation, or high dosages of heavy metals. The major phytoalexins of Eutrema salsugineum (Thellungiella salsuginea), which has recently been established as an extremophile model plant, are probably derivatives of indole glucosinolates, in contrast to Arabidopsis, which synthesizes characteristic camalexin from the glucosinolate precursor indole-3-acetaldoxime. The synthesis of bioactive compounds for adaptation to abiotic stress conditions and for defence against herbivores and pathogen infections is a fundamental survival strategy of plants. In Arabidopsis thaliana, a variety of compounds are synthesized from the intermediate indole-3-acetonitrile (IAN) in response. Eutrema salsugineum has been established recently as an alternative model system for crucifers in addition to Arabidopsis, because of its high tolerance of various. Gene and transcript sequences isolated from Shandong ecotype have been deposited under the species names T. halophila, T. salsuginea and E. salsugineum. According to work by Koch and German [14], the species name T. salsuginea is acceptable, but E. salsugineum, which we refer to in this manuscript, is preferred
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