Ancient bacterial genes linked to plant hormone biosynthesis
image: Phylogenetic analysis of bacterial DCSs with DTCs and TSs. A) phylogenetic tree of α-domains from the five DCSs and bacterial TSs. The α-domain from the bacterial DCSs and the TSs from the same species are indicated by use of the same color, with the DCS α-domain marked with a triangle. Also indicated are four functionally known TSs: KS from B. japonicum (BjKS), KS (PtmT3) from S. platensis, terpentetriene synthase (Tpn3) from Kitasatospora sp. CB02891 and terpentetriene synthase (ORF12, Cyc2) from K. griseola. B) Phylogenetic tree of γβ-didomains from the five bacterial DCSs and bacterial DTCs. The γβ-didomain from the bacterial DCSs and the DTC from the same species, if present, are indicated by use of the same color, with the DCS γβ-didomain marked with a triangle. Also indicated are four functionally known DTCs: CPS from B. japonicum (BjCPS), CPS (PtmT2) from S. platensis, terpentedienyl diphosphate synthase (Tpn2) from Kitasatospora sp. CB02891 and terpentedienyl diphosphate synthase (ORF11, Cyc1) from K. griseola.
Credit: Horticulture Research
A new study has revealed the existence of bifunctional diterpene cyclases/synthases (DCSs) in bacteria, offering compelling evidence that the plant terpene synthase gene family, termed TPS, originated from bacterial genes. The research highlights the identification of five bacterial DCSs, three of which exhibit bifunctional activity, including one enzyme that produces ent-kaurene, a crucial intermediate in plant hormone biosynthesis. This breakthrough supports the theory that the ancestral TPS gene family in plants evolved from a fusion of bacterial genes, shedding new light on the origins of plant terpenoid biosynthesis.
Terpenoids are a diverse and essential group of natural products produced by plants, playing key roles in defense, communication, and hormone regulation. Their biosynthesis begins with prototypical plant terpene synthases (TPSs), enzymes believed to have evolved from a fusion of bacterial diterpene cyclases (DTCs) and terpene synthases (TSs). Despite this hypothesis, the origin of the fusion event remained unclear due to the absence of bifunctional diterpene cyclases/synthases (DCSs) in bacteria, which are crucial for understanding how plants acquired the ability to produce complex terpenoids. This research aims to fill this knowledge gap and provide deeper insights into the evolutionary pathways of TPSs.
Published (DOI: 10.1093/hr/uhae221) on August 3, 2024, in Horticulture Research, this study was led by researchers from the University of Tennessee and Iowa State University. The team identified bifunctional DCSs in bacteria, revealing that these enzymes share structural and functional similarities with plant TPSs, particularly in the production of ent-kaurene, a precursor for gibberellins—key plant hormones. These findings offer strong support for the hypothesis that the plant TPS gene family evolved from a bacterial gene fusion event, bridging the gap between bacterial and plant terpenoid biosynthesis.
The research team undertook extensive genome mining across 15,498 bacterial species, identifying five putative DCS genes. Biochemical analysis confirmed that three of these enzymes displayed bifunctional activity, with one enzyme, GseDCS from Candidatus Sericytochromatia bacterium, producing ent-kaurene. This compound is integral to gibberellin biosynthesis. Remarkably, GseDCS could be split into separate diterpene cyclase (DTC) and terpene synthase (TS) domains, mirroring the structure of plant TPSs. Further sequence alignment and mutational analysis revealed conserved catalytic motifs between bacterial DCSs and plant TPSs, particularly within the CPS and KS active sites. These findings strongly suggest that the ancestral TPS in plants originated from a bacterial DCS gene fusion.
"This discovery not only clarifies the evolutionary origins of TPSs but also highlights the dynamic nature of gene fusion events in bacteria," said Dr. Reuben Peters, a co-author of the study. "The ability to split these bifunctional enzymes into separate domains offers new insights into the structural and functional evolution of terpenoid biosynthesis."
The identification of bifunctional bacterial DCSs has profound implications for evolutionary biology and biotechnology. Understanding the origins of plant TPSs could lead to the development of novel enzymes for industrial terpenoid production, which has applications in agriculture, medicine, and other industries. Furthermore, the study opens up exciting possibilities for exploring the biochemical diversity of terpenoid biosynthesis in bacteria, potentially uncovering new pathways for the production of valuable natural products. The research also emphasizes the role of horizontal gene transfer in shaping the evolution of complex metabolic pathways in plants.
This study not only resolves a long-standing question in plant evolution but also lays the foundation for future investigations into the functional and evolutionary dynamics of terpenoid biosynthesis across different kingdoms of life.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae221
Funding information
This work was supported by an ASAP-SPRINT award from the University of Tennessee, AgResearch (to F.C.) and a grant from the NIH (GM131885 to R.J.P.).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2022. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.