Molecular analyses in wheat and Aegilops tauschii reveal a new orthologue of the leaf rust resistance gene Lr19 on chromosome 7DL of Ae. tauschii

Leaf rust is one of the most devastating wheat diseases worldwide, to which many resistance genes have been successfully introgressed from wheat wild relatives. Though the Thinopyrum ponticum‐derived leaf rust resistance gene Lr19 is widely effective, and previous studies have shown its likely presence in Aegilops tauschii, no thorough investigation has been conducted to confirm this. The current study examined the presence of Lr19 in Ae. tauschii using molecular and bioinformatic analyses. Accordingly, the wheat cultivar Thatcher was used as a susceptible control, and the Lr19‐carrying genotypes; Thatcher + Lr19 (TcLr19) and Agatha were used as resistant controls. Phenotyping using pathotype CDHLQ accompanied with genotyping using two DNA markers verified previous results of the likely presence of an orthologue for Lr19 on chromosome 7DL of Ae. tauschii (AtLr19). Sequencing of the STS GB marker products from Ae. tauschii and TcLr19 showed 99% homology between the corresponding fragments, confirming the phenotyping and genotyping results. Both sequenced fragments matched to the melatonin biosynthesis gene, O‐methyltransferase‐2 (OMT2). A hierarchical gene network was reconstructed using all identified putative genes within a genomic region containing 2.5 cM upstream and downstream of OMT2. Results indicated that numerous important biotic stress‐responsive genes such as RPM1, RGA2, TRIUR3, BURP12 and myosin‐11, were located downstream of melatonin as a master regulator molecule through the OMT2 node. To our knowledge, this is the first report of the identification of an orthologue for Lr19 in Ae. tauschii, which provides insights into the possible regulatory route of this gene.