Data_Sheet_1_The Mosaic Architecture of NRPS-PKS in the Arbuscular Mycorrhizal Fungus Gigaspora margarita Shows a Domain With Bacterial Signature.PDF

As obligate biotrophic symbionts, arbuscular mycorrhizal fungi (AMF) live in association with most land plants. Among them, Gigaspora margarita has been deeply investigated because of its peculiar features, i.e., the presence of an intracellular microbiota with endobacteria and viruses. The genome sequencing of this fungus revealed the presence of some hybrid non-ribosomal peptide synthases-polyketide synthases (NRPS-PKS) that have been rarely identified in AMF. The aim of this study is to describe the architecture of these NRPS-PKS sequences and to understand whether they are present in other fungal taxa related to G. margarita. A phylogenetic analysis shows that the ketoacyl synthase (KS) domain of one G. margarita NRPS-PKS clusters with prokaryotic sequences. Since horizontal gene transfer (HGT) has often been advocated as a relevant evolutionary mechanism for the spread of secondary metabolite genes, we hypothesized that a similar event could have interested the KS domain of the PKS module. The bacterial endosymbiont of G. margarita, Candidatus Glomeribacter gigasporarum (CaGg), was the first candidate as a donor, since it possesses a large biosynthetic cluster involving an NRPS-PKS. However, bioinformatics analyses do not confirm the hypothesis of a direct HGT from the endobacterium to the fungal host: indeed, endobacterial and fungal sequences show a different evolution and potentially different donors. Lastly, by amplifying a NRPS-PKS conserved fragment and mining the sequenced AMF genomes, we demonstrate that, irrespective of the presence of CaGg, G. margarita, and some other related Gigasporaceae possess such a sequence.

作为专性生物共生体，丛枝菌根真菌（AMF）与大多数陆生植物共生。其中，由于Gigaspora margarita具有独特的特征，即存在包含内生细菌和病毒的细胞内微生物群，因此该物种已被深入研究。该真菌的基因组测序揭示了其中存在一些在AMF中很少发现的混合非核糖体肽合成酶-聚酮合成酶（NRPS-PKS）。本研究旨在描述这些NRPS-PKS序列的架构，并探究它们是否存在于与G. margarita相关的其他真菌类群中。系统发育分析表明，G. margarita的一种NRPS-PKS的酮酰合成酶（KS）结构域与原核生物序列聚类。鉴于横向基因转移（HGT）常被提倡为次生代谢基因传播的相关进化机制，我们假设类似事件可能影响了PKS模块的KS结构域。G. margarita的细菌内共生体，即Candidatus Glomeribacter gigasporarum（CaGg），由于它拥有一个涉及NRPS-PKS的大型生物合成簇，因此被视为可能的供体。然而，生物信息学分析并未证实从内生细菌到真菌宿主的直接HGT假设：实际上，内生细菌和真菌序列显示出不同的进化轨迹和潜在的不同的供体。最后，通过扩增NRPS-PKS保守片段并挖掘测序的AMF基因组，我们证明了无论CaGg是否存在，G. margarita以及一些其他相关的Gigasporaceae类群均具有此类序列。