Date: Saturday, January 14, 2012
Time: 1:50 PM
Time: 1:50 PM
Ethylene (ET) has been shown to be important for resistance to necrotrophic pathogens in Arabidopsis. While it remains unclear as to whether Fusarium graminearum is a hemibiotroph or a necrotroph, its necrotrophic mode of growth is most damaging. Thus, ET is a potential candidate for disease resistance signaling. We have used a Virus-Induced Gene Silencing (VIGS) system to silence genes in both the ethylene biosynthesis pathway and the ethylene signaling pathway. The genes were silenced in the resistant variety ‘Ning’ 7840. Upon application of the virus containing a portion of a wheat gene, the plants were screened for conversion from resistance to susceptibility. S-adenosylmethionine synthetase (SAMs) and an Ethylene Response Factor (ERF) in particular demonstrated remarkable conversion to susceptibility upon silencing. The importance of ethylene signaling was also observed using the gaseous inhibitor of ethylene signaling 1-Methylcyclopropene (1-MCP). Ning plants exposed to this inhibitor became significantly more susceptible to F. graminearum than control plants. These plants also become substantially more sensitive to the toxin deoxynivalenol. Additionally, the susceptible variety ‘Bobwhite’ becomes significantly more susceptible when exposed to 1-MCP and challenged with F. graminearum. 1-aminocyclopropane-1-carboxylic-acid (ACC) is a precursor of ethylene and is converted by the enzyme ACC-oxidase into ethylene. Both varieties become significantly more resistant to spray (Type I resistance assay) and point (Type II resistance assay) inoculations when treated with ACC. Our findings contradict recently published work proposing that F. graminearum exploits ethylene signaling to create susceptibility in wheat.