Sulforaphane Modifies Histone H3, Unpacks Chromatin, and Primes Defense

Abstract

Modern crop production calls for agrochemicals that prime plants for enhanced defense. Reliable test systems for spotting priming-inducing chemistry, however, are rare. We developed an assay for the high-throughput search for compounds that prime microbial pattern-induced secretion of antimicrobial furanocoumarins (phytoalexins) in cultured parsley cells. The screen produced 1-isothiocyanato-4-methylsulfinylbutane (sulforaphane; SFN), a secondary metabolite in many crucifers, as a novel defense priming compound. While elucidating SFN's mode of action in defense priming, we found that in Arabidopsis (<i>Arabidopsis</i><i>thaliana</i>) the isothiocyanate provokes covalent modification (K4me3, K9ac) of histone H3 in the promoter and promoter-proximal region of defense genes <i>WRKY6</i> and <i>PDF1</i><i>2</i>, but not <i>PR1</i> SFN-triggered H3K4me3 and H3K9ac coincide with chromatin unpacking in the <i>WRKY6</i> and <i>PDF1</i><i>2</i> regulatory regions, primed <i>WRKY6</i> expression, unprimed <i>PDF1</i><i>2</i> activation, and reduced susceptibility to downy mildew disease (<i>Hyaloperonospora arabidopsidis</i>). Because SFN also directly inhibits <i>H</i><i>arabidopsidis</i> and other plant pathogens, the isothiocyanate is promising for the development of a plant protectant with a dual mode of action.