Long-lasting memory of jasmonic acid-dependent immunity requires DNA demethylation and ARGONAUTE1.

Stress can have long-lasting impacts on plants. Here we report the long-term effects of the stress hormone jasmonic acid (JA) on the defence phenotype, transcriptome and DNA methylome of Arabidopsis. Three weeks after transient JA signalling, 5-week-old plants retained induced resistance (IR) against herbivory but showed increased susceptibility to pathogens. Transcriptome analysis revealed long-term priming and/or upregulation of JA-dependent defence genes but repression of ethylene- and salicylic acid-dependent genes. Long-term JA-IR was associated with shifts in glucosinolate composition and required MYC2/3/4 transcription factors, RNA-directed DNA methylation, the DNA demethylase ROS1 and the small RNA (sRNA)-binding protein AGO1. Although methylome analysis did not reveal consistent changes in DNA methylation near MYC2/3/4-controlled genes, JA-treated plants were specifically enriched with hypomethylated ATREP2 transposable elements (TEs). Epigenomic characterization of mutants and transgenic lines revealed that ATREP2 TEs are regulated by RdDM and ROS1 and produce 21 nt sRNAs that bind to nuclear AGO1. Since ATREP2 TEs are enriched with sequences from IR-related defence genes, our results suggest that AGO1-associated sRNAs from hypomethylated ATREP2 TEs trans-regulate long-lasting memory of JA-dependent immunity.

First European interlaboratory study of the analysis of benzoxazinone derivatives in plants by liquid chromatography.

Six laboratories from four different countries participated in the first European interlaboratory comparison exercise within the framework of the "Fate and toxicity of allelochemicals (natural plant toxins) in relation to environment and consumer" (FATEALLCHEM) European Union Project. The study, organized between November 2002 and March 2003, involved the analyses of seven benzoxazinone derivatives in two standard solutions and one purified extract of root material. Results are reported from the first phase of the study that examined the variability associated with different detection methods and different laboratories. The analytical strategies were based on liquid chromatography (LC) with diode array detection, LC coupled to mass spectrometry (MS) and LC coupled to tandem MS. When data from all laboratories were pooled, the relative standard deviation values ranged from 2 to 14% for the determination of target compounds in standard solutions, and between 19 and 47% for the analysis in root material. Comparison of the three detection techniques leads to the conclusion that MS approaches are the most accurate and precise techniques for the determination of benzoxazinone derivatives at ng/microL level in plant material.