Characterization of Oxidosqualene Cyclases in Brassicaceae: the ABCs (Arabidopsis, Brassica and Capsella)

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dc.contributor.advisorMatsuda, Seiichi P. T.en_US
dc.creatorJin, Jingen_US
dc.date.accessioned2019-10-24T21:19:37Zen_US
dc.date.available2020-05-01T05:01:10Zen_US
dc.date.created2019-05en_US
dc.date.issued2019-10-23en_US
dc.date.submittedMay 2019en_US
dc.date.updated2019-10-24T21:19:37Zen_US
dc.description.abstractOne major class of plant secondary metabolites is the triterpenes, whose biosynthesis from oxidosqualene is catalyzed by oxidosqualene cyclases (OSCs). This thesis describes the characterization of OSCs from plants within the Brassicaceae family, which include the model species Arabidopsis thaliana and Capsella rubella as well as the crop species Brassica rapa and Brassica oleracea. Detailed product profiles of those cyclases are combined with phylogenetic analysis, synteny analysis, active-site prediction, plant tissue extraction and transcriptome analysis to explore enzyme mechanisms and evolutionary relationships within the OSC family. First, detailed product profiles are constructed for four Arabidopsis thaliana OSCs. Those cyclases exemplify the range of product specificity among OSCs, ranging from the 94% specific At PEN4 to the multi-functional cyclase At LUP5 which makes two major products at similar levels. Despite their varying product specificity, all those OSCs form many minor products. Next, the characterization of three OSCs from Brassica species is detailed. Bra032185 was determined to be an astertarone A synthase, which is the first reported OSC with 6/6/6/5 20R stereospecificity. Bra039929 is the first reported euphol synthase and is another 6/6/6/5 20R specific cyclase. In addition, Bol021540 was amplified from broccoli seedling RNAs and it was determined to be a mixed-amyrin synthase. Those results were combined with Brassica plant extraction results to explore the triterpene biosynthesis in this species. Lastly, the complete characterization of all Capsella rubella OSCs is described. The triterpene biosynthetic capability of this plant includes one cycloartenol synthase, five functional OSCs in the secondary metabolism and one pseudogene. The only secondary metabolic OSC conserved between A. thaliana and C. rubella is camelliol C synthase (LUP3). In addition, three C. rubella cyclases show similarity to their A. thaliana counterparts but different products are made. Overall, the comparison of OSCs across species illustrates the fast divergence of plant secondary metabolism and explores OSC evolution among the Brassicaceae family. The OSC family showcases rapid enzyme functional evolution as evident by neofunctionalization and convergent evolution, and thus it can be a valuable model for enzyme evolution studies.en_US
dc.embargo.terms2020-05-01en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.citationJin, Jing. "Characterization of Oxidosqualene Cyclases in Brassicaceae: the ABCs (Arabidopsis, Brassica and Capsella)." (2019) Diss., Rice University. <a href="https://hdl.handle.net/1911/107502">https://hdl.handle.net/1911/107502</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/107502en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjecttriterpeneen_US
dc.subjectplanten_US
dc.subjectplant secondary metabolismen_US
dc.subjectoxidosqualene cyclaseen_US
dc.subjectBrassicaceaeen_US
dc.subjectbrassicaen_US
dc.subjectcapsellaen_US
dc.subjectArabidopsisen_US
dc.titleCharacterization of Oxidosqualene Cyclases in Brassicaceae: the ABCs (Arabidopsis, Brassica and Capsella)en_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentBiochemistry and Cell Biologyen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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