Abstract
As sessile organisms, plants have to endure a wide variety of biotic and abiotic stresses, and accordingly they have evolved intricate and rapidly inducible defense strategies associated with the activation of a battery of genes. Among other mechanisms, changes in chromatin structure are thought to provide a flexible, global, and stable means for the regulation of gene transcription. In support of this idea, we demonstrate here that the Arabidopsis (Arabidopsis thaliana) histone methyltransferase SET DOMAIN GROUP8 (SDG8) plays a crucial role in plant defense against fungal pathogens by regulating a subset of genes within the jasmonic acid (JA) and/or ethylene signaling pathway. We show that the loss-of-function mutant sdg8-1 displays reduced resistance to the necrotrophic fungal pathogens Alternaria brassicicola and Botrytis cinerea. While levels of JA, a primary phytohormone involved in plant defense, and camalexin, a major phytoalexin against fungal pathogens, remain unchanged or even above normal in sdg8-1, induction of several defense genes within the JA/ethylene signaling pathway is severely compromised in response to fungal infection or JA treatment in mutant plants. Both downstream genes and, remarkably, also upstream mitogen-activated protein kinase kinase genes MKK3 and MKK5 are misregulated in sdg8-1. Accordingly, chromatin immunoprecipitation analysis shows that sdg8-1 impairs dynamic changes of histone H3 lysine 36 methylation at defense marker genes as well as at MKK3 and MKK5, which normally occurs upon infection with fungal pathogens or methyl JA treatment in wild-type plants. Our data indicate that SDG8-mediated histone H3 lysine 36 methylation may serve as a memory of permissive transcription for a subset of defense genes, allowing rapid establishment of transcriptional induction.
Highlights
As sessile organisms, plants have to endure a wide variety of biotic and abiotic stresses, and they have evolved intricate and rapidly inducible defense strategies associated with the activation of a battery of genes
H3K36me3 and H3K36me1 were undetectable in sdg8-1 (Supplemental Fig. S7; Supplemental Table S7). These results indicate that dynamic changes in H3K36 methylation at PDF1.2a and VSP2 occur in response to fungal infection and methyl jasmonate (MeJA) treatment and show that SET DOMAIN GROUP8 (SDG8)-mediated H3K36me3 is directly associated with transcriptional induction of these defense genes
We have demonstrated that SDG8 and H3K36 methylation are involved in the establishment of a chromatin state required for inducible defense against necrotrophic fungal pathogens
Summary
Plants have to endure a wide variety of biotic and abiotic stresses, and they have evolved intricate and rapidly inducible defense strategies associated with the activation of a battery of genes. Changes in chromatin structure are thought to provide a flexible, global, and stable means for the regulation of gene transcription In support of this idea, we demonstrate here that the Arabidopsis (Arabidopsis thaliana) histone methyltransferase SET DOMAIN GROUP8 (SDG8) plays a crucial role in plant defense against fungal pathogens by regulating a subset of genes within the jasmonic acid (JA) and/or ethylene signaling pathway. Our data indicate that SDG8-mediated histone H3 lysine 36 methylation may serve as a memory of permissive transcription for a subset of defense genes, allowing rapid establishment of transcriptional induction To compensate for their sessile nature, plants have evolved intricate and diverse strategies enabling them to survive and adapt to a broad range of biotic stresses, including insect, herbivore, and pathogen attacks. ATX1, a TrxG member involved in H3K4 trimethylation (Alvarez-Venegas and Avramova, 2005), was shown to be necessary for the induction of WRKY70, a transcription factor gene in the SA pathway involved in defense against bacterial pathogens (Alvarez-Venegas et al, 2007)
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