Abstract
Disease resistance (R) genes are key components in plant immunity. Here, we show that Arabidopsis (Arabidopsis thaliana) E3 ubiquitin ligase genes HISTONE MONOUBIQUITINATION1 (HUB1) and HUB2 regulate the expression of R genes SUPPRESSOR OF npr1-1, CONSTITUTIVE1 (SNC1) and RESISTANCE TO PERONOSPORA PARASITICA4. An increase of SNC1 expression induces constitutive immune responses in the bonzai1 (bon1) mutant, and the loss of HUB1 or HUB2 function reduces SNC1 up-regulation and suppresses the bon1 autoimmune phenotypes. HUB1 and HUB2 mediate histone 2B (H2B) monoubiquitination directly at the SNC1 R gene locus to regulate its expression. In addition, SNC1 and HUB1 transcripts are moderately up-regulated by pathogen infection, and H2B monoubiquitination at SNC1 is enhanced by pathogen infection. Together, this study indicates that H2B monoubiquitination at the R gene locus regulates its expression and that this histone modification at the R gene locus has an impact on immune responses in plants.
Highlights
Disease resistance (R) genes are key components in plant immunity
Fine tuning R gene expression is important for plant defense responses and, balancing plant immunity, growth, and development. This is exemplified by the large impact of SNC1 expression on growth and immunity, because an increase of its transcript level leads to autoimmune responses and greatly reduced stature (Zhang et al, 2003; Yang and Hua, 2004; Yang et al, 2006; Li et al, 2010b; Zhu et al, 2013)
We show that HISTONE MONOUBIQUITINATION1 (HUB1) directly modifies the chromatin of the SNC1 locus and regulates the expression of SNC1 and two other genes in the RPP5 gene cluster
Summary
We show that Arabidopsis (Arabidopsis thaliana) E3 ubiquitin ligase genes HISTONE MONOUBIQUITINATION1 (HUB1) and HUB2 regulate the expression of R genes SUPPRESSOR OF npr, CONSTITUTIVE1 (SNC1) and RESISTANCE TO PERONOSPORA PARASITICA4. This study indicates that H2B monoubiquitination at the R gene locus regulates its expression and that this histone modification at the R gene locus has an impact on immune responses in plants. In addition to its critical role in development, HUB1 was recently shown to be required for resistance to the necrotrophic pathogen Botrytis cinerea (Dhawan et al, 2009) These results indicate that H2Bub plays important roles in plant stress responses
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