Aerolysin-like proteins from Armillaria ostoyae with potential roles in plant pathogenicity reveal a distant evolutionary relationship to toadfish natterins

Abstract

Understanding the evolutionary distribution and functional roles of toxins across diverse taxa remains a fundamental challenge in fungal biology. Aerolysin-like beta-pore-forming toxins are widely distributed across multiple kingdoms of life, yet their specific occurrence and structural diversity within the fungal kingdom remain poorly characterized. In our current study, we address this gap by investigating candidate aerolysin-like proteins in the basidiomycete Armillaria ostoyae using an integrated framework combining structural modeling, comparative genomics, and transcriptomic datasets spanning multiple developmental stages. Our results demonstrate that these candidate proteins are actively transcribed throughout the fungal life cycle, with consistent expression maintained in mature fruiting-body tissues. Notably, we show that the specific gene ARMOST_18480 undergoes significant upregulation under plant-invasive conditions, strongly supporting its role as a putative pathogenicity-associated factor. Structural characterization revealed a modular architecture with deeply conserved pore-forming domains including Alanine-Glycine-Isoleucine-Proline (AGIP)-like loop variants homologous to vertebrate natterins from Thalassophryne nattereri, despite low overall sequence identity. Importantly, phylogenetic inference robustly resolves these Armillaria proteins within distinct fungal lineages well-separated from their vertebrate counterparts. Together, these findings significantly expand the known evolutionary distribution of the aerolysin superfamily and identify key candidates for future functional validation regarding pore-forming activity, plant pathogenicity, and mushroom-associated bioactivity.