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Barkman, T. J.

Publications and source records attributed to Barkman, T. J..

2 recordsLinked to original sources

Systematics of the fleshy-fruited Sonerileae (Melastomataceae)

With approximately 1080 species, Sonerileae is the second largest tribe in the Melastomataceae. Approximately 40% of Sonerileae species belong to fleshy-fruited genera (Catanthera, Heteroblemma, Kendrickia, Medinilla, Pachycentria, and Plethiandra). Relatively few species, especially of the fleshy-fruited taxa, have been sampled for phylogenetic study. Consequently, there is huge uncertainty resulting in many unanswered questions about their evolutionary history, including the monophyly of the largest genus, Medinilla. In this study, the phylogeny of the fleshy-fruited Sonerileae was reconstructed using 385 nuclear and 81 plastid protein-coding loci recovered from target capture. Our study revealed that the fleshy fruited Sonerileae are polyphyletic and belong to three lineages. Kendrickia is sister to an Afrotropical endemic clade. Heteroblemma and Catanthera belong to a second clade and are most closely related to some Phyllagathis and Driessenia species. Medinilla forms a third clade, and includes Pachycentria and Plethiandra. Within Medinilla, fifteen clades are identified and characterized. To make Medinilla monophyletic, the genus is redefined to include Pachycentria and Plethiandra. Major lineages identified within Medinilla lay the groundwork for an infrageneric classification system. Areas of the phylogenetic tree with high conflict or weak sampling are identified to aid further studies in the tribe.

plant biology↗

Yerba mate (Ilex paraguariensis) genome provides new insights into convergent evolution of caffeine biosynthesis

Yerba mate (Ilex paraguariensis) is an economically important crop marketed for the elaboration of mate, the third-most widely consumed caffeine-containing infusion worldwide. Here we report the first genome assembly of this species, which has a total length of 1.06 Gb and contains 53,390 protein-coding genes. Comparative analyses revealed that the large yerba mate genome size is partly due to a whole-genome duplication (Ip-) during the early evolutionary history of Ilex, in addition to the hexaploidization event ({gamma}) shared by core eudicots. Characterization of the genome allowed us to clone the genes encoding methyltransferase enzymes that catalyse multiple reactions required for caffeine production. To our surprise, this species has converged upon a different biochemical pathway compared to that of its relatives, coffee and tea. In order to gain insight into the structural basis for the convergent enzyme activities, we obtained a crystal structure for the terminal enzyme in the pathway that forms caffeine. The structure reveals that convergent solutions have evolved for substrate positioning because different amino acid residues facilitate a different substrate orientation such that efficient methylation occurs in the independently evolved enzymes in yerba mate and coffee. While our results show phylogenomic constraint limits the genes coopted for convergence of caffeine biosynthesis, the x-ray diffraction data suggests structural constraints are minimal for the convergent evolution of individual reactions.

plant biology↗