Transcriptome Analysis Based on Lr19-Virulent Mutants Strain Provides Clues for the Pathogenicity-Related Genes and Effectors of Puccinia Triticina

Background: Wheat leaf rust caused by Puccinia triticina (Pt) remains one of the most destructive diseases of common wheat worldwide. Cultivating resistant cultivars is an effective way to control this disease, but race-specific resistance can be overcome quickly due to the rapid evolution of Pt populations. The critical to control wheat leaf rust is to understand the pathogenicity mechanisms of Pt. Results: In this study, the spores of the Pt race PHNT (wheat leaf rust resistance gene Lr19-avirulent isolate) were mutagenized with ethyl methanesulfonate (EMS) and two Pt Lr19-virulent mutants named M1 and M2 were isolated, suggesting that they carry mutations affecting the Lr19-specific avirulent factor. RNA sequencing was performed on samples collected from the wheat cultivars Chinese Spring and TcLr19 that were infected by wild-type (WT) PHNT and the two Lr19-virulent mutant isolates at 14 days post-inoculation (dpi). The assembled transcriptome data were compared to the reference genome “Pt 1-1 BBBD Race 1.” A total of 216 differentially expressed genes (DEGs) were found from three different sample comparisons including M1-vs-WT, M2-vs-WT, and M1-vs-M2. Of these DEGs, 29 common DEGs were shared between M1-vs-WT and M2-vs-WT comparisons. Among the 216 DEGs encoding proteins, 30 were predicted to be effector candidates. Then 6 effector candidates (PTTG_27844, PTTG_05290, PTTG_27401, PTTG_27224, PTTG_26282, PTTG_25521) were verified that these genes were differentially expressed during Pt infection by quantitative real-time PCR (qRT-PCR) and were validated on tobacco, and the results showed that PTTG_27401 could inhibit progress of cell death (PCD) induced by BAX.Conclusions: Our results showed that a large number of genes participate in the interaction between Pt and TcLr19, which will provide valuable resources for the identification and targeting of AvrLr19 effector candidates and pathogenesis-related genes. Furthermore, our analyses are of great significance to reveal the pathogenesis of Pt.