February 11, 2015

Boutanaev et al. "Investigation of terpene diversification across multiple sequenced plant genomes"

Alexander M. Boutanaev, Tessa Moses, Jiachen Zi, David R. Nelson, Sam T. Mugford, Reuben J. Peters, and Anne Osbourn

This actually came out the end of last year, but since terpene synthases have been a theme lately, this one is well worth including. Boutanaev et al. used comparative genomics to identify associations between two groups of enzymes that are important for making terpenes: terpene synthases (TS), which generate olefinic hydrocarbons or alcohols from prenylated diphosphate precursors of varying chain lengths, and cytochrome P450s (CYPs), which introduce various oxygen functionalities into the carbon skeleton through regiospecific oxidation reactions once the diphosphate has been removed.  By comparing TS/CYP gene pairs from many sequenced plant genomes, they determined that the evolution of terpenoid biosynthetic pathways, which requires TS and CYP activities among others, has occurred differently in monocot and dicot lineages. In monocots, individual TY and CYP genes were recombined in dynamic genome rearrangements whereas new terpenoid diversity was acquired in dicots by gene duplication and subfunctionalization of TS/CYP pairs. Their approach also facilitated the identification of functional pairing of TS and CYP genes in previously unknown gene clusters.

vol. 112 no. 1 Alexander M. Boutanaev,  E81–E88, doi: 10.1073/pnas.1419547112
The original paper can be seen here 

From the article


Plants produce an array of specialized metabolites, including chemicals that are important as medicines, flavors, fragrances, pigments and insecticides. The vast majority of this metabolic diversity is untapped. Here we take a systematic approach toward dissecting genetic components of plant specialized metabolism. Focusing on the terpenes, the largest class of plant natural products, we investigate the basis of terpene diversity through analysis of multiple sequenced plant genomes. The primary drivers of terpene diversification are terpenoid synthase (TS) “signature” enzymes (which generate scaffold diversity), and cytochromes P450 (CYPs), which modify and further diversify these scaffolds, so paving the way for further downstream modifications. Our systematic search of sequenced plant genomes for all TS and CYP genes reveals that distinct TS/CYP gene pairs are found together far more commonly than would be expected by chance, and that certain TS/CYP pairings predominate, providing signals for key events that are likely to have shaped terpene diversity. We recover TS/CYP gene pairs for previously characterized terpene metabolic gene clusters and demonstrate new functional pairing of TSs and CYPs within previously uncharacterized clusters. Unexpectedly, we find evidence for different mechanisms of pathway assembly in eudicots and monocots; in the former, microsyntenic blocks of TS/CYP gene pairs duplicate and provide templates for the evolution of new pathways, whereas in the latter, new pathways arise by mixing and matching of individual TS and CYP genes through dynamic genome rearrangements. This is, to our knowledge, the first documented observation of the unique pattern of TS and CYP assembly in eudicots and monocots. 

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