The NAC (NAM, ATAF1/2, and CUC2) is a defense-associated transcription factor (TF) family that positively regulates defense responses to pathogen infection. TaNAC069 positively regulates resistance in wheat to Puccinia triticina (Pt). However, the molecular mechanism of its interaction with a Pt effector is not clear. We found that Pt effector Pt-1234 interacts with TaNAC069 to subvert host immunity during Pt infection. Quantitative real-time PCR analysis showed that expression of Pt-1234 was significantly up-regulated during the early stage of Pt infection. Protein-mediated cell death assays in wheat showed that the Pt-1234 protein was unable to induce cell death in wheat near-isogenic lines carrying different leaf rust resistance genes, whereas it suppressed BAX-induced cell death in leaves of Nicotiana benthamiana. Silencing of Pt-1234 by host-induced gene silencing (HIGS) significantly reduced the virulence of Pt in the susceptible wheat variety Thatcher. The C subdomain of TaNAC069 was responsible for its interaction with Pt-1234, and the E subdomain was required for TaNAC069-mediated defense responses to Pt in planta. These findings indicate that Pt utilizes Pt-1234 to interact with wheat transcription factor TaNAC069 through its C subdomain, thereby modulating wheat immunity.

Puccinia triticina (Pt), as the causal agent of wheat leaf rust, employs a plethora of effector proteins to modulate wheat immunity for successful colonization. Understanding the molecular mechanisms underlying Pt effector-mediated wheat susceptibility remains largely unexplored. In this study, an effector Pt_21 was identified to interact with the apoplast-localized wheat thaumatin-like protein TaTLP1 using a yeast two-hybrid assay and the Pt_21-TaTLP1 interaction was characterized. The interaction between Pt_21 and TaTLP1 was validated by in vivo co-immunoprecipitation assay. A TaTLP1 variant, TaTLP1^C71A, that was identified by the site-directed mutagenesis failed to interact with Pt_21. Pt_21 was able to suppress Bax-mediated cell death in leaves of Nicotiana benthamiana and inhibit TaTLP1-mediated antifungal activity. Furthermore, infiltration of recombinant protein Pt_21 into leaves of transgenic wheat line overexpressing TaTLP1 enhanced the disease development of leaf rust compared to that in wild-type leaves. These findings demonstrate that Pt_21 suppresses host defense response by directly targeting wheat TaTLP1 and inhibiting its antifungal activity, which broadens our understanding of the molecular mechanisms underlying Pt effector-mediated susceptibility in wheat.

Thaumatin-like protein (TLP) plays an important role in combating plant pathogen infection. Common root rot caused by Bipolaris sorokiniana and leaf rust caused by Puccinia triticina (Pt) are major fungal diseases in wheat. The disease responses of TaTLP1-overexpressing transgenic lines (TaTLP1-OE) were evaluated after inoculation with each pathogen. The TaTLP1-OE lines had no apparent differences in tiller number and 1000-kernel weight from the wild type Jinan Wheat No. 1 (JW1), whereas resistance to leaf rust and common root rot was improved, resulting from activated peroxidase and β-1,3-glucanase after B. sorokiniana infection, and reactive oxygen species-related genes were upregulated in TaTLP1-OE lines after Pt infection. These results indicated that stable expression of TaTLP1 increased resistance against both diseases.