Encoding a glutathione S-transferase (GST) and conferring resistance to Fusarium head blight (FHB), Fhb7 was successfully isolated from the newly assembled Thinopyrum elongatum genome by researchers, with blasting searches revealing that Thinopyrum gained Fhb7 through horizontal gene transfer from an endophytic Epichloë species. On the contrary, our molecular evidence reveals that the homologs of Fhb7 are distributed commonly in Triticeae. Other than Thinopyrum, the Fhb7 homologs were also detected in four other genera, Elymus, Leymus, Roegneria and Pseudoroegneria, respectively. Sequence comparisons revealed that the protein sequences were at least 94% identical across all of the Fhb7 homologs in Triticeae plants, which in turn suggested that the horizontal gene transfer of the Fhb7 might have occurred before Triticeae differentiation instead of Thinopyrum. The multiple Fhb7 homologs detected in some Triticeae accessions and wheat-Thinopyrum derivatives might be attributed to the alloploid nature and gene duplication during evolution. In addition, we discovered that some wheat-Thinopyrum derivatives carrying the Fhb7 homologs had a completely different reaction to Fusarium head blight, which made us question the ability of the GST-encoding Fhb7 to resist FHB.

The lack of resistance resources is a major bottleneck for wheat Fusarium head blight (FHB) resistance breeding. Three wheat- Th. elongatum FHB resistant translocation lines have been developed and used for wheat breeding without yield penalty. Transcriptomic analysis identified a derivative glutathione S-transferase transcript T26102, which was homologous to Fhb7 and induced dramatically by Fusarium graminearum . Unlike other studies, Fhb7 homologs were detected not only in Thinopyrum but also in Elymus , Leymus , Pseudoroegeria and Roegeria . We also found that several wheat- Th. ponticum derivatives carrying Fhb7 and its homologs were highly susceptible to FHB. Moreover, the transgenic plants expressing Fhb7 and its homolog on different backgrounds did not improve the FHB resistance. One Sentence Summary: The GST-encoding Fhb7 candidate cannot improve Fusarium head blight resistance in wheat breeding.