How does "RALPH" effector BEC1054 work? Investigating the mode of action of an RNAse-Like effector Protein associated with Haustoria in barley powdery mildew
P. SPANU (1), M. Przydacz (1), H. Pennington (1), R. Jones (1) (1) Imperial College London, United Kingdom

The Blumeria graminis genomes encode hundreds of candidate effectors organised in several families. In the barley powdery mildew fungus, B. graminis f. sp. hordei, we have previously shown that a large subset of these proteins are structurally similar to archetypal fungal RNAses. Moreover, two highly expressed and closely related paralog effectors, BEC1054 and BEC1011, are necessary for full development of haustoria and disease. BEC1054 and the other members of the Family 21 effector genes are all induced during infection, but there are subtle differences in the expression dynamics during infectious development. Expression of recombinant BEC1054 as a stable transgene in wheat and transiently in Nicotiana benthamiana leads to increased susceptibility to adapted biotrophic pathogens. Here we report the high-resolution 3D structure of BEC1054 derived from X-ray crystallography and NMR. This leads us to the identification of amino acid residues which may interact with a nucleic acid substrate. We test by a structure-informed targeted mutagenesis what the function of these amino acids are in the interaction with the plant. We observe that meJA induced modification of rRNA is inhibited by BEC1054 expressed as a transgene in wheat, and by infection with B. graminis. This supports the hypothesis that BEC1054 is delivered to the host cell, and interferes with the action of host Ribosome Inactivating Proteins (e.g. JIP60) and promotes suppression of a branch of plant immunity mediated by mJA.

Abstract Number: P9-233
Session Type: Poster