Luo Hong, Cai Qing, Lüli Yunjiao, Li Xuan, Sinha Rohita, Hallen-Adams Heather E, Yang Zhu L
Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, Yunnan, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
IMA Fungus. 2018 Jul;9:225-242. doi: 10.5598/imafungus.2018.09.02.01. Epub 2018 Aug 1.
The biosynthetic pathway for amanitins and related cyclic peptides in deadly () mushrooms represents the first known ribosomal cyclic peptide pathway in the . Amanitins are found outside of the genus in distantly related agarics () and (). A long-standing question in the field persists: why is this pathway present in these phylogenetically disjunct agarics? Two deadly mushrooms, and , were deep sequenced, and sequences of biosynthetic genes encoding MSDINs (cyclic peptide precursor) and prolyl oligopeptidases ( and ) were obtained. The two species yielded 29 and 18 MSDINs, respectively. In addition, two MSDIN sequences were cloned from basidiomes. The toxin MSDIN genes encoding amatoxins or phallotoxins from the three genera were compared, and a phylogenetic tree constructed. Prolyl oligopeptidase B (POPB), a key enzyme in the biosynthetic pathway, was used in phylogenetic reconstruction to infer the evolutionary history of the genes. Phylogenies of and based on both coding and amino acid sequences showed very different results: while genes clearly reflected the phylogeny of the host species, did not; strikingly, it formed a well-supported monophyletic clade, despite that the species belong to different genera in disjunct families. , a known house-keeping gene, was shown to be restricted in a branch containing only species and the phylogeny resembled that of those species. Phylogenetic analyses of MSDIN and genes showed tight coordination and disjunct distribution. A gene tree was compared with a corresponding species tree, and distances and substitution rates were compared. The result suggested genes have significant smaller distances and rates than the house-keeping , discounting massive gene loss. Under this assumption, the incongruency between the gene tree and species tree was shown with strong support. Additionally, k-mer analyses consistently cluster and genes, while is distinct. Our result suggests that horizontal gene transfer (HGT), at least between and was involved in the acquisition of genes, which may shed light on the evolution of the α-amanitin biosynthetic pathway.
致命鹅膏菌及相关环肽的生物合成途径是担子菌中已知的首个核糖体环肽途径。鹅膏毒素在亲缘关系较远的伞菌目蘑菇如高大环柄菇属和离褶伞属中也有发现。该领域长期存在一个问题：为何这条途径会出现在这些系统发育上不连续的伞菌中？对两种致命蘑菇——致命鹅膏菌和鳞柄白鹅膏菌进行了深度测序，获得了编码MSDINs（环肽前体）和脯氨酰寡肽酶（POPA和POPB）的生物合成基因序列。这两种鹅膏菌分别产生了29个和18个MSDINs。此外，从豹斑鹅膏菌的子实体中克隆了两个MSDIN序列。对来自这三个属的编码鹅膏毒素或鬼笔毒素的毒素MSDIN基因进行了比较，并构建了系统发育树。脯氨酰寡肽酶B（POPB）是生物合成途径中的关键酶，用于系统发育重建以推断基因的进化历史。基于编码序列和氨基酸序列构建的高大环柄菇属和离褶伞属的系统发育树显示出非常不同的结果：高大环柄菇属基因清楚地反映了宿主物种的系统发育，而离褶伞属基因则没有；令人惊讶的是，尽管这些物种属于不同科的不同属，但它形成了一个得到有力支持的单系分支。已知的管家基因肌动蛋白被证明局限于一个仅包含高大环柄菇属物种的分支中，其系统发育与那些高大环柄菇属物种相似。对MSDIN和肌动蛋白基因的系统发育分析显示出紧密的协调性和不连续的分布。将一个肌动蛋白基因树与相应的物种树进行比较，并比较了距离和替换率。结果表明，与管家基因肌动蛋白相比，MSDIN基因的距离和替换率显著更小，排除了大量基因丢失的情况。在此假设下，基因树与物种树之间的不一致得到了有力支持。此外，k-mer分析始终将高大环柄菇属和离褶伞属基因聚类在一起，而豹斑鹅膏菌基因则是不同的。我们的结果表明，至少在高大环柄菇属和离褶伞属之间存在水平基因转移（HGT），这可能为α-鹅膏毒素生物合成途径的进化提供线索。
