Abstract: Accelerated gene evolution is a hallmark of pathogen adaptation and is crucial to enable host-range expansions and host-jumps. Effector proteins that are translocated into the host cell to facilitate infection evolve rapidly, leading to increased rates of adaptive mutations and presence/absence polymorphisms. Adaptive evolution has been demonstrated within Magnaporthe oryzae lineages, as with the AVR-Pik effector of the rice lineage. However, adaptive effector evolution associated with host jumps, i.e. across host-specific lineages, is poorly understood. Here, we describe a ubiquitous effector, APikL2, which effector belongs to a diverse effector family distributed across multiple host-specific lineages of M. oryzae. All effectors in this family show lineage-specific presence/absence polymorphisms with the exception APikL2, which is conserved across all lineages. Using biochemical, biophysical, and structural methods, we show an adaptive mutation in the binding interface expands the target-binding spectrum of APikL2 to heavy-metal associated domain containing proteins (HMAs). By reconstructing the ancestry and analysing the structural consequences of allelic diversification, we further identify a common mechanism of effector specialization across the family that involves two major interfaces. Together, our results provide detailed information about the molecular evolution of plant pathogen effectors and suggest effector diversification in a certain host-specific lineage that enabled host jumps.

Bio: Adam Bentham first entered into plant immunity as an undergraduate student at Flinders University, South Australia, where he worked on the TIR domains of the flax NLRs M and L6 under the guidance of Peter Anderson. In 2014, he began a PhD between the labs of Peter Anderson and Bostjan Kobe (University of Queensland), where he trained as a biochemist & structural biologist. During his PhD, Adam worked under the supervision of Simon Williams (ANU) on the N-terminal domains of several NLRs including CC domains of Sr33, MLA10 and Rx, and the TIR domain of RPP1, addressing how self-association of the N-terminal domains of NLRs is related to signalling activity. In 2017, Adam joined the lab of Mark Banfield at the John Innes Centre, Norwich, as postdoctoral scientist on a shared ERC grant with Sophien Kamoun, where he works on the molecular mechanism of effector recognition by integrated domains in NLRs.