The hijacking of a wheat Exo70-like protein by a fungal pathogen triggers disease
Tan spot is an economically important fungal disease of wheat that occurs globally. In this necrotrophic pathosystem, pathogen effectors are recognized by wheat genes in an inverse gene-for-gene manner, leading to the hijacking of host defense mechanisms and ultimately disease susceptibility. Here, we identified the tan spot susceptibility gene Tsc2 through positional cloning, mutagenesis, and transgenic complementation. Tsc2 encodes a diverged form of the exocyst subunit Exo70FX15 that localizes to the nucleus and cytoplasm and does not interact directly with the fungal effector. A 21‑nucleotide deletion in Tsc2 occurred in durum wheat more than a century ago and subsequently spread to common wheat through breeding practices, which allowed recognition of the pathogen effector and subsequent hijacking of the host immune system. We demonstrate that elimination of Tsc2 through conventional breeding using a diagnostic marker or disruption of Tsc2 by gene editing can be used to improve tan spot resistance in wheat.