A single amino acid polymorphism in a conserved effector of the multihost blast fungus pathogen expands host-target binding spectrum

Abstract

Accelerated gene evolution is a hallmark of pathogen adaptation and specialization following host-jumps. However, the molecular processes associated with adaptive evolution between host-specific lineages of a multihost plant pathogen remain poorly understood. In the blast fungus Magnaporthe oryzae (Syn. Pyricularia oryzae), host specialization on different grass hosts is generally associated with dynamic patterns of gain and loss of virulence effector genes that tend to define the distinct genetic lineages of this pathogen. Here, we unravelled the biochemical and structural basis of adaptive evolution of APikL2, an exceptionally conserved paralog of the well-studied rice-lineage specific effector AVR-Pik. Whereas AVR-Pik and other members of the six-gene AVR-Pik family show specific patterns of presence/absence polymorphisms between grass-specific lineages of M. oryzae, APikL2 stands out by being ubiquitously present in all blast fungus lineages from 13 different host species. Using biochemical, biophysical and structural biology methods, we show that a single aspartate to asparagine polymorphism expands the binding spectrum of APikL2 to host proteins of the heavy-metal associated (HMA) domain family. This mutation maps to one of the APikL2-HMA binding interfaces and contributes to an altered hydrogen-bonding network. By combining phylogenetic ancestral reconstruction with an analysis of the structural consequences of allelic diversification, we revealed a common mechanism of effector specialization in the AVR-Pik/APikL2 family that involves two major HMA-binding interfaces. Together, our findings provide a detailed molecular evolution and structural biology framework for diversification and adaptation of a fungal pathogen effector family following host-jumps.

pOPIN-GG: A resource for modular assembly in protein expression vectors

“…The different pOPIN-GG acceptors are crosscompatible for co-expression, allowing for ease of co-expression and purification of protein complexes. Finally, the utility of the pOPIN-GG vectors presented here have already been successfully tested by the community for the expression and purification of a fungal effector from Parastagonospora nodorum (Outram et al, 2021), as well as for detailing the structural mechanisms underpinning the evolution of Magnaporthe oryzae effectors for a specific host target (Bentham et al, 2021).…”

Functional diversification gave rise to allelic specialization in a rice NLR immune receptor pair

“…The Pik NLR pair occurs as allelic series in both Japonica and Indica rice cultivars (Chaipanya et al, 2017; Costanzo and Jia, 2010; Hua et al, 2012; Xu et al, 2008). The AVR-Pik effectors are also polymorphic and present signatures of selection (Bentham et al, 2021; Bialas et al, 2018; Yoshida et al, 2009). Allelic Pik NLRs have differential recognition specificities for the AVR-Pik variants (De la Concepcion et al, 2021; Kanzaki et al, 2012), which is underpinned by differential effector binding to the Pik-1 HMA domain (De la Concepcion et al, 2018; De la Concepcion et al, 2021; Maqbool et al, 2015).…”

Regressive evolution of an effector following a host jump in the Irish Potato Famine Pathogen Lineage

“…However, very few of these studies have specifically focused on how effectors evolve to maintain their function in the context of a new cellular environment. A recent study looked at effector-target co-evolutionary dynamics in the blast fungus Magnaporthe oryzae (10). The authors identified a highly conserved effector, APikL2, that is present across all assayed host-specific pathogen lineages (10).…”

“…A recent study looked at effector-target co-evolutionary dynamics in the blast fungus Magnaporthe oryzae (10). The authors identified a highly conserved effector, APikL2, that is present across all assayed host-specific pathogen lineages (10). They found that a single naturally-occurring amino acid polymorphism in APikL2 expands the range of host targets that this effector can bind to, and conclude that the mutation is likely adaptive in the lineages where it is found (10).…”

“…The authors identified a highly conserved effector, APikL2, that is present across all assayed host-specific pathogen lineages (10). They found that a single naturally-occurring amino acid polymorphism in APikL2 expands the range of host targets that this effector can bind to, and conclude that the mutation is likely adaptive in the lineages where it is found (10). Other examples of research investigating the process of host specialization at the molecular level come from the Phytophthora clade 1c species (11).…”