Kemen Ariane C, Agler Matthew T, Kemen Eric
Max Planck Research Group Fungal Biodiversity, Max Planck Institute for Plant Breeding Research, Carl-von-Linne Weg 10, 50829, Cologne, Germany.
New Phytol. 2015 Jun;206(4):1207-28. doi: 10.1111/nph.13284. Epub 2015 Jan 26.
Research on obligate biotrophic plant parasites, which reproduce only on living hosts, has revealed a broad diversity of filamentous microbes that have independently acquired complex morphological structures, such as haustoria. Genome studies have also demonstrated a concerted loss of genes for metabolism and lytic enzymes, and gain of diversity of genes coding for effectors involved in host defense suppression. So far, these traits converge in all known obligate biotrophic parasites, but unexpected genome plasticity remains. This plasticity is manifested as transposable element (TE)-driven increases in genome size, observed to be associated with the diversification of virulence genes under selection pressure. Genome expansion could result from the governing of the pathogen response to ecological selection pressures, such as host or nutrient availability, or to microbial interactions, such as competition, hyperparasitism and beneficial cooperations. Expansion is balanced by alternating sexual and asexual cycles, as well as selfing and outcrossing, which operate to control transposon activity in populations. In turn, the prevalence of these balancing mechanisms seems to be correlated with external biotic factors, suggesting a complex, interconnected evolutionary network in host-pathogen-microbe interactions. Therefore, the next phase of obligate biotrophic pathogen research will need to uncover how this network, including multitrophic interactions, shapes the evolution and diversity of pathogens.
对专性活体营养型植物寄生虫（仅在活寄主上繁殖）的研究揭示了丝状微生物的广泛多样性，这些微生物独立获得了复杂的形态结构，如吸器。基因组研究还表明，代谢基因和裂解酶基因协同丢失，而编码参与抑制寄主防御的效应子的基因多样性增加。到目前为止，这些特征在所有已知的专性活体营养型寄生虫中都有体现，但仍存在意想不到的基因组可塑性。这种可塑性表现为转座元件（TE）驱动的基因组大小增加，观察到这与选择压力下毒力基因的多样化有关。基因组扩张可能是由于病原体对生态选择压力（如寄主或养分可用性）的反应，或对微生物相互作用（如竞争、超寄生和有益合作）的反应受到调控所致。通过交替进行有性和无性周期，以及自交和异交来平衡扩张，这些过程可控制种群中转座子的活性。反过来，这些平衡机制的普遍程度似乎与外部生物因素相关，这表明在寄主 - 病原体 - 微生物相互作用中存在一个复杂的、相互关联的进化网络。因此，专性活体营养型病原体研究的下一阶段需要揭示这个网络，包括多营养相互作用，如何塑造病原体的进化和多样性。
