Summary: In this study, we report new insights into the function of a wheat (Triticum aestivum) MYB gene TaPIMP1 through overexpression and underexpression, and its underlying mechanism in wheat. Electrophoretic mobility shift and yeast‐one‐hybrid assays indicated that TaPIMP1 can bind to five MYB‐binding sites including ACI, and activate the expression of the genes with the cis‐element, confirming that TaPIMP1 is an MYB transcription activator. TaPIMP1‐overexpressing transgenic wheat exhibited significantly enhanced resistance to the fungal pathogen Bipolaris sorokiniana and drought stresses, whereas TaPIMP1‐underexpressing transgenic wheat showed more susceptibility to the stresses compared with untransformed wheat, revealing that TaPIMP1 positively modulates host‐defense responses to B. sorokiniana and drought stresses. Microarray analysis showed that a subset of defense‐ and stress‐related genes were up‐regulated by TaPIMP1. These genes, including TaPIMP1, RD22, TLP4 and PR1a, were regulated by ABA and salicylic acid (SA). TaPIMP1‐underexpressing transgenic wheat showed compromised induction of these stress‐responsive genes following ABA and SA treatments. In summary, TaPIMP1, as a positive molecular linker, mediates resistance to B. sorokiniana and drought stresses by regulation of stress‐related genes in ABA‐ and SA‐signaling pathways in wheat. Furthermore, TaPIMP1 may provide a transgenic tool for engineering multiple‐resistance wheat in breeding programs.

Sharp eyespot disease (primarily caused by the pathogen Rhizoctonia cerealis) and freezing stress are important yield limitations for the production of wheat (Triticum aestivum). Here, we report new insights into the function and underlying mechanisms of an ethylene response factor (ERF) in wheat, Pathogen-Induced ERF1 (TaPIE1), in host responses to R. cerealis and freezing stresses. TaPIE1-overexpressing transgenic wheat exhibited significantly enhanced resistance to both R. cerealis and freezing stresses, whereas TaPIE1-underexpressing wheat plants were more susceptible to both stresses relative to control plants. Following both stress treatments, electrolyte leakage and hydrogen peroxide content were significantly reduced, and both proline and soluble sugar contents were elevated in TaPIE1-overexpressing wheat, whereas these physiological traits in TaPIE1-underexpressing wheat exhibited the opposite trend. Microarray and quantitative reverse transcription-polymerase chain reaction analyses of TaPIE1-overexpressing and -underexpressing wheat plants indicated that TaPIE1 activated a subset of defense- and stress-related genes. Assays of DNA binding by electrophoretic mobility shift and transient expression in tobacco (Nicotiana tabacum) showed that the GCC boxes in the promoters of TaPIE1-activated genes were essential for transactivation by TaPIE1. The transactivation activity of TaPIE1 and the expression of TaPIE1-activated defense- and stress-related genes were significantly elevated following R. cerealis, freezing, and exogenous ethylene treatments. TaPIE1-mediated responses to R. cerealis and freezing were positively modulated by ethylene biosynthesis. These data suggest that TaPIE1 positively regulates the defense responses to R. cerealis and freezing stresses by activating defense- and stress-related genes downstream of the ethylene signaling pathway and by modulating related physiological traits in wheat.

Plant caffeic acid 3-O-methyltransferase (COMT) has been implicated in the lignin biosynthetic pathway through catalyzing the multi-step methylation reactions of hydroxylated monomeric lignin precursors. However, genetic evidence for its function in plant disease resistance is poor. Sharp eyespot, caused primarily by the necrotrophic fungus Rhizoctonia cerealis, is a destructive disease in hexaploid wheat (Triticum aestivum L.). In this study, a wheat COMT gene TaCOMT-3D, is identified to be in response to R. cerealis infection through microarray-based comparative transcriptomics. The TaCOMT-3D gene is localized in the long arm of the chromosome 3D. The transcriptional level of TaCOMT-3D is higher in sharp eyespot-resistant wheat lines than in susceptible wheat lines, and is significantly elevated after R. cerealis inoculation. After R. cerealis inoculation and disease scoring, TaCOMT-3D-silenced wheat plants exhibit greater susceptibility to sharp eyespot compared to unsilenced wheat plants, whereas overexpression of TaCOMT-3D enhances resistance of the transgenic wheat lines to sharp eyespot. Moreover, overexpression of TaCOMT-3D enhances the stem mechanical strength, and lignin (particular syringyl monolignol) accumulation in the transgenic wheat lines. These results suggest that TaCOMT-3D positively contributes to both wheat resistance against sharp eyespot and stem mechanical strength possibly through promoting lignin (especially syringyl monolignol) accumulation.