Light influences how the fungal toxin deoxynivalenol affects plant cell death and defense responses.

The Fusarium mycotoxin deoxynivalenol (DON) can cause cell death in wheat (Triticum aestivum), but can also reduce the level of cell death caused by heat shock in Arabidopsis (Arabidopsis thaliana) cell cultures. We show that 10 µg mL(-1) DON does not cause cell death in Arabidopsis cell cultures, and its ability to retard heat-induced cell death is light dependent. Under dark conditions, it actually promoted heat-induced cell death. Wheat cultivars differ in their ability to resist this toxin, and we investigated if the ability of wheat to mount defense responses was light dependent. We found no evidence that light affected the transcription of defense genes in DON-treated roots of seedlings of two wheat cultivars, namely cultivar CM82036 that is resistant to DON-induced bleaching of spikelet tissue and cultivar Remus that is not. However, DON treatment of roots led to genotype-dependent and light-enhanced defense transcript accumulation in coleoptiles. Wheat transcripts encoding a phenylalanine ammonia lyase (PAL) gene (previously associated with Fusarium resistance), non-expressor of pathogenesis-related genes-1 (NPR1) and a class III plant peroxidase (POX) were DON-upregulated in coleoptiles of wheat cultivar CM82036 but not of cultivar Remus, and DON-upregulation of these transcripts in cultivar CM82036 was light enhanced. Light and genotype-dependent differences in the DON/DON derivative content of coleoptiles were also observed. These results, coupled with previous findings regarding the effect of DON on plants, show that light either directly or indirectly influences the plant defense responses to DON.

Components of the gene network associated with genotype-dependent response of wheat to the Fusarium mycotoxin deoxynivalenol.

The Fusarium mycotoxin deoxynivalenol (DON) facilitates fungal spread within wheat tissue and the development of Fusarium head blight disease. The ability of wheat spikelets to resist DON-induced bleaching is genotype-dependent. In wheat cultivar (cv.) CM82036 DON resistance is associated with a quantitative trait locus, Fhb1, located on the short arm of chromosome 3B. Gene expression profiling (microarray and real-time RT-PCR analyses) of DON-treated spikelets of progeny derived from a cross between cv. CM82036 and the DON-susceptible cv. Remus discriminated ten toxin-responsive transcripts associated with the inheritance of DON resistance and Fhb1. These genes do not exclusively map to Fhb1. Based on the putative function of the ten Fhb1-associated transcripts, we discuss how cascades involving classical metabolite biotransformation and sequestration processes, alleviation of oxidative stress and promotion of cell survival might contribute to the host response and defence against DON.

Retrotransposon and gene activation in wheat in response to mycotoxigenic and non-mycotoxigenic-associated Fusarium stress.

Despite inhibition of protein synthesis being its mode of action, the trichothecene mycotoxin deoxynivalenol (DON) induced accumulation of transcripts encoding translation elongation factor 1alpha (EF-1alpha), class III plant peroxidase (POX), structure specific recognition protein, basic leucine zipper protein transcription factor (bZIP), retrotransposon-like homologs and genes of unknown function in the roots of wheat cultivars CM82036 and Remus. Fusarium head blight (FHB) studies using Fusarium graminearum and its trichothecene-minus (Tri5 ( - )) mutant derivative and adult plant DON tests showed that these transcripts were responsive to both mycotoxigenic- and non-mycotoxigenic-associated Fusarium stress. In tests using the parents 'CM82036', 'Remus' and 14 double-haploid progeny that segregated for quantitative trait locus (QTL) Fhb1 on chromosome 3BS (syn. Qfhs.ndsu-3BS) (from 'CM82036' that confers DON tolerance), bZIP expression was significantly more DON-up-regulated in lines that inherited this QTL. Basal accumulation of the bZIP transcript in spikelets treated with Tween20 (control), DON and in DON-relative to Tween20-treated spikelets was negatively correlated with DON-induced bleaching above (but not below) the treated spikelets (AUDPC(DON)) (r = -0.41, -0.75 and -0.72, respectively; P < or = 0.010). bZIP-specific PCR analysis of 'Chinese spring' and its 3BS deletion derivatives indicated that bZIP is located in chromosomal region(s) other than 3BS. These results, and the fact that a homologous cold-regulated wheat bZIP (wLIP19) maps to group 1 chromosomes suggests that wheat bZIP may participate in defence response cascades associated with Fhb1 and that there is a cross-talk between biotic and abiotic stress signalling pathways.