A reminiscence of evolutionary hourglass: The pattern of ergot alkaloid gene divergence in Claviceps purpurea

Citation

M. Liu, W. Findlay, P. Shoukouhi, K. Dadej, H. D. T. Nguyen, J. G. Menzies, K. A. Seifert. 2019. A reminiscence of evolutionary hourglass: The pattern of ergot alkaloid gene divergence in Claviceps purpurea.

Abstract

The pattern of genetic divergence during embryo development in animal and plants was interpreted as following an early conservation model until an hourglass model was proposed in 1990s, i.e. diverged early and late stages connected by a conserved middle stage. The debate over which model holds true is inconclusive, while comparative genomics provided evidence to support the hourglass model at the molecular level. According to the biogenetic hypothesis, ontogeny recapitulates phylogeny. It is possible that these models exist in other evolutionary processes, such as metabolic biosynthesis pathways. Mycotoxins produced by ergot fungi have significant detrimental and beneficial impacts on the economy, ecology and health, leading to the in-depth study and clarification of the biosynthesis pathway, and a good system to test these hypotheses. In Claviceps purpurea and close relatives, ergot alkaloids synthesis (EAS) involves 12 genes expressed at the early (dmaW, easF, easC, easE), middle (easD, easA, easG) and late (easH, lpsA, lpsB, lpsC) stages in the biosynthetic pathway (cloA in both middle and late stages). Full DNA sequences of 11 EAS genes (excluding lpsA) were extracted from complete genomes of 30 strains belonging to six closely related Claviceps species. Comparison of DNA polymorphisms showed that divergence level (K) was apparently lower in the middle stages, especially easD and easA, resembling the hourglass model. This pattern was observed among six species and within C. purpurea and confirmed using a tree-based divergence analysis. We believe this is the first report of hourglass model in a secondary metabolic pathway.

Publication date

2019-02-01

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