Re-acquisition of the brittle rachis trait via a transposon insertion in domestication gene Q during wheat de-domestication.

De-domestication is a unique evolutionary process during which crops re-acquire wild-like traits to survive and persist in agricultural fields without the need for human cultivation. The re-acquisition of seed dispersal mechanisms is crucial for crop de-domestication. Common wheat is an important cereal crop worldwide. Tibetan semi-wild wheat is a potential de-domesticated common wheat subspecies. However, the crucial genes responsible for its brittle rachis trait have not been identified. Genetic mapping, functional analyses and phylogenetic analyses were completed to identify the gene associated with Qbr.sau-5A, which is a major locus for the brittle rachis trait of Tibetan semi-wild wheat. The cloned Qbr.sau-5A gene is a new Q allele (Qt ) with a 161-bp transposon insertion in exon 5. Although Qt is expressed normally, its encoded peptide lacks some key features of the APETALA2 family. The abnormal functions of Qt in developing wheat spikes result in brittle rachises. Phylogenetic and genotyping analyses confirmed that Qt originated from Q in common wheat and is naturally distributed only in Tibetan semi-wild wheat populations. The identification of Qt provides new evidence regarding the origin of Tibetan semi-wild wheat, and new insights into the re-acquisition of wild traits during crop de-domestication.

Functional Analysis of FgNahG Clarifies the Contribution of Salicylic Acid to Wheat (Triticum aestivum) Resistance against Fusarium Head Blight.

Salicylic acid (SA) is a key defense hormone associated with wheat resistance against Fusarium head blight, which is a severe disease mainly caused by Fusarium graminearum. Although F. graminearum can metabolize SA, it remains unclear how this metabolic activity affects the wheat⁻F. graminearum interaction. In this study, we identified a salicylate hydroxylase gene (FG05_08116; FgNahG) in F. graminearum. This gene encodes a protein that catalyzes the conversion of SA to catechol. Additionally, FgNahG was widely distributed within hyphae. Disrupting the FgNahG gene (ΔFgNahG) led to enhanced sensitivity to SA, increased accumulation of SA in wheat spikes during the early infection stage and inhibited development of head blight symptoms. However, FgNahG did not affect mycotoxin production. Re-introducing a functional FgNahG gene into the ΔFgNahG mutant recovered the wild-type phenotype. Moreover, the expression of FgNahG in transgenic Arabidopsis thaliana decreased the SA concentration and the resistance of leaves to F. graminearum. These results indicate that the endogenous SA in wheat influences the resistance against F. graminearum. Furthermore, the capacity to metabolize SA is an important factor affecting the ability of F. graminearum to infect wheat plants.