Niche differentiation and evolution of the wood decay machinery in the invasive fungus Serpula lacrymans

Ecological niche breadth and the mechanisms facilitating its evolution are fundamental to understanding adaptation to changing environments, persistence of generalist and specialist lineages and the formation of new species. Woody substrates are structurally complex resources utilized by organisms with specialized decay machinery. Wood-decaying fungi represent ideal model systems to study evolution of niche breadth, as they vary greatly in their host range and preferred decay stage of the substrate. In order to dissect the genetic basis for niche specialization in the invasive brown rot fungus Serpula lacrymans, we used phenotyping and integrative analysis of phylogenomic and transcriptomic data to compare this species to wild relatives in the Serpulaceae with a range of specialist to generalist decay strategies. Our results indicate specialist species have rewired regulatory networks active during wood decay towards decreased reliance on enzymatic machinery, and therefore nitrogen-intensive decay components. This shift was likely accompanied with adaptation to a narrow tree line habitat and switch to a pioneer decomposer strategy, both requiring rapid colonization of a nitrogen-limited substrate. Among substrate specialists with narrow niches, we also found evidence for pathways facilitating reversal to generalism, highlighting how evolution may move along different axes of niche space.

生态位宽度（Ecological niche breadth）及其演化促进机制，是理解生物适应环境变化、维持广适性与特化类群存续，以及新物种形成的核心基础。木质基质是结构复杂的资源，仅携带有特化腐朽酶系的生物方可利用此类资源。木腐真菌（wood-decaying fungi）是研究生态位宽度演化的理想模式系统，因其宿主范围与偏好的基质腐朽阶段存在显著差异。为解析入侵性褐腐真菌干朽菌（Serpula lacrymans）的生态位特化遗传基础，我们采用表型分型（phenotyping）及系统基因组学（phylogenomics）与转录组学（transcriptomics）数据的整合分析策略，将该物种与干朽菌科（Serpulaceae）中拥有从特化到广适性腐朽策略的野生近缘物种进行对比。研究结果显示，特化类群在木质腐朽过程中激活的调控网络已发生重编程，转向降低对酶系统的依赖，进而减少高氮消耗型腐朽组分的合成。这一转变可能伴随了对狭窄林线生境的适应，以及向先锋分解者策略的转变——这两类过程均需在氮限制基质中实现快速定殖。在生态位狭窄的基质特化类群中，我们还发现了支持其向广适性生态位逆转的通路证据，这揭示了演化如何沿着生态位空间的不同维度进行推进。