Bio-Protection Research Centre, Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.
Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA.
New Phytol. 2013 Apr;198(2):525-535. doi: 10.1111/nph.12161. Epub 2013 Mar 1.
Plant pathogens use a complex arsenal of weapons, such as toxic secondary metabolites, to invade and destroy their hosts. Knowledge of how secondary metabolite pathways evolved is central to understanding the evolution of host specificity. The secondary metabolite dothistromin is structurally similar to aflatoxins and is produced by the fungal pine pathogen Dothistroma septosporum. Our study focused on dothistromin genes, which are widely dispersed across one chromosome, to determine whether this unusual distributed arrangement evolved from an ancestral cluster. We combined comparative genomics and population genetics approaches to elucidate the origins of the dispersed arrangement of dothistromin genes over a broad evolutionary time-scale at the phylum, class and species levels. Orthologs of dothistromin genes were found in two major classes of fungi. Their organization is consistent with clustering of core pathway genes in a common ancestor, but with intermediate cluster fragmentation states in the Dothideomycetes fungi. Recombination hotspots in a D. septosporum population matched sites of gene acquisition and cluster fragmentation at higher evolutionary levels. The results suggest that fragmentation of a larger ancestral cluster gave rise to the arrangement seen in D. septosporum. We propose that cluster fragmentation may facilitate metabolic retooling and subsequent host adaptation of plant pathogens.
植物病原体利用一系列复杂的武器，如有毒次生代谢物，来入侵和破坏它们的宿主。了解次生代谢途径的进化如何是理解宿主特异性进化的核心。次生代谢物多托菌素在结构上与黄曲霉毒素相似，由真菌松材病原体多托曲霉菌产生。我们的研究集中在多托菌素基因上，这些基因广泛分布在一条染色体上，以确定这种不寻常的分散排列是否是从祖先簇进化而来的。我们结合比较基因组学和群体遗传学方法，在门、纲和种水平上阐明了多托菌素基因在广泛进化时间尺度上的分散排列的起源。在两种主要真菌类群中发现了多托菌素基因的同源基因。它们的组织与核心途径基因在共同祖先中的聚类一致，但在 Dothideomycetes 真菌中存在中间聚类片段状态。在 D. septosporum 种群中的重组热点与基因获取和聚类片段化的位点在更高的进化水平上相匹配。结果表明，较大的祖先聚类的片段化导致了 D. septosporum 中所见的排列。我们提出，聚类片段化可能促进植物病原体的代谢重构和随后的宿主适应。
