ISWI chromatin remodeling factors repress PAD4-mediated plant immune responses in Arabidopsis.

Chromatin remodeling proteins modulate nucleosome dynamic to affect global gene expression and other cellular processes. Their roles in the regulation of plant growth and development have been widely reported, but their roles in plant stress resistance, especially disease resistance, have not been extensively investigated. Here, we show that the Arabidopsis Immunity Switch (ISWI) chromatin-remodeling factors CHR11 and CHR17, are negative regulators of plant disease resistance. The loss of both CHR11 and CHR17 function led to upregulation of a large set of defense response genes in the absence of pathogen infection. The chr11 single mutant showed enhanced resistance against a virulent pathogen Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). Further analysis revealed that mutation of Phytoalexin Deficient4 (PAD4) reduced the upregulation of defense gene expression as well as resistance against Pst DC3000 in the chr11 chr17 double mutant. However, mutation of PAD4 does not rescue the growth defects of chr11 chr17. Together, our study revealed a function of ISWI in repressing defense response under non-pathogenic conditions and indicates distinct target genes of ISWI in regulating plant growth and plant immunity.