A barley UDP-glucosyltransferase provides high levels of resistance to trichothecenes and Fusarium Head Blight in cereals

Abstract

Fusarium Head Blight (FHB) is a devastating disease that leads to severe economic losses to worldwide wheat (Triticum aestivum) and barley (Hordeum vulgare L.) production. During FHB disease development, the main causal fungal pathogen, Fusarium graminearum can infect a single spikelet and cause disease symptoms throughout the spike in susceptible wheat. Moreover, F. graminearum produces trichothecene mycotoxins (eg., deoxynivalenol (DON), nivalenol (NIV) and their derivatives) that facilitate FHB disease development, and toxin contamination of the grain poses a significant threat to human and animal health. Two major types of resistance have been identified and deployed in breeding programs including: type I (resistance to initial infection) and type II (resistance to spread of the symptoms). Although worldwide efforts have focused on germplasm screening and QTL mapping of FHB resistance, unfortunately, resistance to FHB is quantitatively controlled and only partial. Thus, research efforts have expanded to identifying genes and deploying them in transgenic wheat. Previous gene expression analysis in the barley cultivar ‘Morex’ led to discovery of a UDP-glucosyltransferase gene, HvUGT13248, that was shown to provide DON resistance in transgenic yeast and Arabidopsis thaliana via conjugation of DON to DON-3-O-glucoside (D3G), a much less toxic derivative. To test this promising gene in wheat, we developed transgenic wheat expressing HvUGT13248 and showed that these transgenic plants exhibited significant reduction of disease spread (type II resistance) in the spike compared with nontransformed controls. Expression of HvUGT13248 in transgenic wheat rapidly and efficiently conjugated DON to D3G. Under field conditions, FHB severity was variable between different transgenic lines; however, in some years the transgenic wheat showed significantly less severe disease phenotypes compared with the nontransformed controls. Moreover, HvUGT13248 is also capable of converting NIV to the detoxified derivative, NIV-3-O-β-D-glucoside (NIV3G). An enzymatic assay using HvUGT13248 purified from Escherichia coli showed that HvUGT13248 efficiently catalyzed NIV to NIV3G. Overexpression in yeast, Arabidopsis thaliana and wheat showed enhanced NIV resistance when grown on media containing different levels of NIV. Increased ability to convert nivalenol to NIV3G was observed in transgenic wheat, which also exhibits type II resistance to a NIV-producing F. graminearum strain. Transgenic wheat expressing HvUGT13248 also provides type II resistance to F. graminearum strains producing 3-ADON and NX-2, and resistance to root growth inhibition in 3,15-diANIV-containing media. Moreover, the HvUGT13248 transgene was introgressed into the elite wheat cultivars ‘Rollag’ and ‘Linkert’, and greenhouse point inoculation results showed that HvUGT13248 improved FHB resistance in elite backgrounds. HvUGT13248 overexpression in transgenic barley also enhanced DON resistance observed in a root assay. In conclusion, HvUGT13248 is a highly effective FHB resistant gene that can detoxify a wide spectrum of trichothecene chemotypes. Thus, the mechanism of resistance is by rapidly detoxifying trichothecenes to their glucoside forms.