Arabidopsis Displays Centromeric DNA Hypomethylation and Cytological Alterations of Heterochromatin Upon Attack by Pseudomonas syringae

Abstract

Plant tissues display major alterations upon the perception of microbial pathogens. Changes of cytoplasmic and apoplastic components that sense and transduce plant defenses have been extensively characterized. In contrast, less information is available about modifications affecting the plant nuclear genome under these circumstances. Here, we investigated whether the Arabidopsis thaliana DNA methylation status is altered in tissues responding to the attack of Pseudomonas syringae pv. tomato DC3000. We applied amplified fragment length polymorphism analysis to monitor cytosine methylation at anonymous 5'-CCGG-3' and 5'-GATC-3' sites in naive and infected samples. Plant genomic fragments reducing methylation upon infection, including peri/centromeric repeats such as the 180-bp unit, Athila retrotansposon, and a portion of the nuclear insertion of mitochondrial DNA, were isolated and characterized. P. syringae pv. tomato-induced hypomethylation was detected by high-performance liquid chromatography assays and at the molecular level it did not seem to equally affect all 5-methyl cytosine (5-mC) residues. Nuclei from challenged tissues displayed structural chromatin alterations, including loosening of chromocenters, which also were stimulated by avirulent P. syringae pv. tomato, but not by the P. syringae pv. tomato hrpL- mutant. Finally, P. syringae pv. tomato-induced hypomethylation was found to occur in the absence of DNA replication, suggesting that it involves an active demethylation mechanism. All these responses occurred at 1 day postinfection, largely preceding massive plant cell death generated by pathogen attack.

Next-Generation Systemic Acquired Resistance

“…Hence, DNA hypomethylation in the ddc mutant mimics transgenerational priming of SA-dependent defense. Since infection by PstDC3000 induces DNA hypomethylation in Arabidopsis (Pavet et al, 2006), our results indicate that transgenerational resistance from PstDC3000-infected plants is transmitted by hypomethylated DNA.…”

“…In particular DNA hypomethylation has been associated with plant defense. For instance, Arabidopsis responds to infection by PstDC3000 by hypomethylation of genomic DNA (Pavet et al, 2006). Furthermore, inbreeding of the Arabidopsis decrease in DNA methylation1 mutation, causing genome-wide DNA hypomethylation, gives rise to a heritable but metastable defense allele, called bal1, which confers NPR1-dependent resistance (Stokes et al, 2002;Yi and Richards, 2009).…”

“…By contrast, there is ample evidence for transmission of DNA methylation to following generations. It is also known that PstDC3000 triggers DNA hypomethylation in Arabidopsis (Pavet et al, 2006). To examine the role of DNA methylation in PstDC3000-induced transgenerational resistance, we compared transgenerational resistance phenotypes between wild-type plants and the drm1drm2cmt3 triple mutant (ddc), which is reduced in non-CpG DNA methylation (Chan et al, 2006).…”

Is DNA methylation modulated by wounding-induced oxidative burst in maize?

“…When maize seedlings were exposed to cold stress, a genome-wide demethylation occurred in root tissues, but not in leaf blades or stem (Steward et al, 2002). Hypomethylation was also induced upon pathogen infection in tobacco (Wada et al, 2004) and Arabidopsis (Pavet et al, 2006). Some hypomethylated genes involved in stress responses were found to be transcriptionally activated (Wada et al, 2004;Choi and Sano, 2007).…”

Early genomic responses to salicylic acid in Arabidopsis

“…tomato strain DC3000 that expresses the AvrRpm1 gene (Pst/AvrRpm1). A bacterial suspension of 5 9 10 6 cfu/ml in 10 mM MgCl 2 was infiltrated on the abaxial side of the leaves with a 1 ml syringe (Pavet et al 2006). Mock-treated plants were infiltrated with 10 mM MgCl 2 .…”