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. Significant efforts are being placed on understanding the secretomes of various pathogens as secreted peptides are believed to be the best candidates for avirulence effectors. In this work, a P. triticina haustorial cDNA library was evaluated for the presence of proteins containing secretion signals. Ten predicted proteins were found in the library, of which two were expressed in haustorial fractions. Three of the secreted proteins, Pt3, Pt12 and Pt27, were used in biolistic experiments to determine whether they could induce hypersensitive cell death, which is commonly observed in incompatible rust interactions with wheat leaf rust resistance genes. When Pt3 was co-bombarded with a β-glucoronidase (GUS)-expressing vector into wheat isolines with resistance genes Lr9 or Lr24, a significant reduction of GUS expression was observed, presumably due to hypersensitive cell death. In other co-bombardment experiments, Pt27 induced a significant reduction in GUS expression in the Lr26 isoline. These results suggest that Pt3 and Pt27 may function in avirulence against wheat leaf rust in resistant genotypes.