Two small secreted proteins from Puccinia triticina induce reduction of ß-glucoronidase transient expression in wheat isolines containing Lr9, Lr24 and Lr26

Little is known about the molecular interaction of wheat and leaf rust (Puccinia triticina Eriks). However, genomic tools are now becoming available so that the host-pathogen interactions can be better understood. Upon infecting, many pathogens secrete into their hosts a large number of small proteins, the virulence factors that help suppress the plant defense responses and coax the host into releasing nutrients for the benefit of the microbial pathogen for its own survival and propagation. Significant efforts are put into understanding the precise function of this so-called secretome of various pathogens. Importantly, some secreted virulence factors are believed to be avirulence effectors, that is, their action or interaction with host proteins triggers a defense response and hence stops the pathogen from further infection. Such host proteins are often the products of resistance genes and are valuable for breeding resistance into crops. Therefore, secreted pathogen effectors can be valuable tools to identify resistance genes for breeding purposes, and to understand defense in crop plants. In this work, ten P. triticina predicted secreted effector proteins were identified of which two were shown to be expressed during wheat infection. Three of these candidate secreted effector proteins, Pt3, Pt12, and Pt27, were used in a functional screen, using biolistic experiments, to determine whether they could induce hypersensitive cell death, which is indicative of interactions with wheat leaf rust resistance genes in wheat. We got indication that Pt3 may interact with wheat resistance genes Lr9 or Lr24, and that Pt27 may interact with wheat resistance gene Lr26 isoline. These results suggest that Pt3 and Pt27 may function in avirulence against wheat leaf rust in resistant genotypes, and may be used to search for the matching resistance genes.