Deoxynivalenol Biosynthesis-Related Gene Expression During Wheat Kernel Colonization by Fusarium graminearum

Abstract

Deoxynivalenol (DON) is a potent mycotoxin and virulence factor produced by Fusarium graminearum. We examined the expression of the core DON biosynthetic gene Tri5 during wheat head infection of susceptible and resistant cultivars and susceptible cultivars treated with strobilurin fungicides (e.g., azoxystrobin). DON was quantified to correlate expression with toxin accumulation. The highest Tri5 expression relative to housekeeping genes occurred at the infection front. As infection progressed, earliest-infected kernels showed diminished relative Tri5 expression but Tri5 expression never ceased during the 21 days observed. Azoxystrobin treatment showed no significant effect on either relative Tri5 expression or DON quantity. The resistant cultivar ‘Alsen’ showed minimal spread of the fungus, with no fungus detected by day 21. DON was not detected in significant quantities in Alsen in the later stages sampled. In Wheaten, DON levels were negligible at 8 days postinoculation (dpi), with detectable DON at later-sampled time points. Tri5 was detected even in fully senesced kernels 21 dpi. Our data demonstrate the presence of Tri5 transcripts in a susceptible cultivar over a much longer time period than has been previously documented. This suggests the ability of the fungus to rapidly resume toxin biosynthesis in dried infected grain should conducive environmental conditions be present, and provides a possible mechanism for high DON levels in asymptomatic grain.

The completed genome sequence of the pathogenic ascomycete fungus Fusarium graminearum

“…Deoxynivalenol (DON) produced by Fusarium graminearum is a potent B-type trichothecene mycotoxin [33] and virulence factor to disease formation in wheat floral tissue [34]. Commonly found in harvested cereal grains, DON lowers grain quality and is a serious health concern to humans and animals [35].…”

Impact of Fusarium graminearum inoculum availability and fungicide application timing on Fusarium head blight in wheat

“…DON functions as a virulence factor in the colonization of wheat by F. graminearum, allowing hyphae to colonize the rachis node and move from spikelet to spikelet (Brown et al, 2010;Jansen et al, 2005). DON has been shown to be most active at the infection front and transcription of DON biosynthesis genes has been detected within 24 h of initial infection (Hallen-Adams et al, 2011). DON levels have also been shown to increase in wheat tissue up to 45 DAA and to be positively influenced by increased levels of moisture during grain fill up to 30 DAA (Cowger and Arellano, 2013).…”

Fusarium Mycotoxins and Their Role in Plant–Pathogen Interactions

“…DON is produced early in the interaction, in specialized infection structures [103] and TRI genes are transcribed in the moving infection front [104]. An immunohistochemistry study with antisera raised against DON showed that DON can move ahead of the fungus and presumably conditions susceptibility by interfering with translation.…”