No abstract

Summary Taxonomically‐restricted orphan genes play an important role in environmental adaptation, as recently demonstrated by the fact that the Pooideae‐specific orphan TaFROG (Triticum aestivum Fusarium Resistance Orphan Gene) enhanced wheat resistance to the economically devastating Fusarium head blight (FHB) disease. Like most orphan genes, little is known about the cellular function of the encoded protein TaFROG, other than it interacts with the central stress regulator TaSnRK1α. Here, we functionally characterized a wheat (T. aestivum) NAC–like transcription factor TaNACL‐D1 that interacts with TaFROG and investigated its’ role in FHB using studies to assess motif analyses, yeast transactivation, protein‐protein interaction, gene expression and the disease response of wheat lines overexpressing TaNACL‐D1. TaNACL‐D1 is a Poaceae‐divergent NAC transcription factor that encodes a Triticeae‐specific protein C‐terminal region with transcriptional activity and a nuclear localisation signal. The TaNACL‐D1/TaFROG interaction was detected in yeast and confirmed in planta, within the nucleus. Analysis of multi‐protein interactions indicated that TaFROG could form simultaneously distinct protein complexes with TaNACL‐D1 and TaSnRK1α in planta. TaNACL‐D1 and TaFROG are co‐expressed as an early response to both the causal fungal agent of FHB, Fusarium graminearum and its virulence factor deoxynivalenol (DON). Wheat lines overexpressing TaNACL‐D1 were more resistant to FHB disease than wild type plants. Thus, we conclude that the orphan protein TaFROG interacts with TaNACL‐D1, a NAC transcription factor that forms part of the disease response evolved within the Triticeae.

The mycotoxin deoxynivalenol (DON) serves as a plant disease virulence factor for the fungi Fusarium graminearum and F. culmorum during the development of Fusarium head blight (FHB) disease on wheat. A wheat cytochrome P450 gene from the subfamily CYP72A, TaCYP72A, was cloned from wheat cultivar CM82036. TaCYP72A was located on chromosome 3A with homeologs present on 3B and 3D of the wheat genome. Using gene expression studies, we showed that TaCYP72A variants were activated in wheat spikelets as an early response to F. graminearum, and this activation was in response to the mycotoxic Fusarium virulence factor deoxynivalenol (DON). Virus induced gene silencing (VIGS) studies in wheat heads revealed that this gene family contributes to DON resistance. VIGS resulted in more DON-induced discoloration of spikelets, as compared to mock VIGS treatment. In addition to positively affecting DON resistance, TaCYP72A also had a positive effect on grain number. VIGS of TaCYP72A genes reduced grain number by more than 59%. Thus, we provide evidence that TaCYP72A contributes to host resistance to DON and conclude that this gene family warrants further assessment as positive contributors to both biotic stress resistance and grain development in wheat.