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Description
Premise of the study: Land-plant plastid genomes have only rarely undergone significant changes in gene content and order. Thus, discovery of additional examples adds power to tests for causes of such genome-scale structural changes.
Methods: Using next-generation sequence data, we assembled the plastid genome of saguaro cactus and probed the nuclear genome for transferred plastid genes and functionally related nuclear genes. We combined these results with available data across Cactaceae and seed plants more broadly to infer the history of gene loss and to assess the strength of phylogenetic association between gene loss and loss of the inverted repeat (IR).
Key results: The saguaro plastid genome is the smallest known for an obligately photosynthetic angiosperm (∼113 kb), having lost the IR and plastid ndh genes. This loss supports a statistically strong association across seed plants between the loss of ndh genes and the loss of the IR. Many nonplastid copies of plastid ndh genes were found in the nuclear genome, but none had intact reading frames; nor did three related nuclear-encoded subunits. However, nuclear pgr5, which functions in a partially redundant pathway, was intact.
Conclusions: The existence of an alternative pathway redundant with the function of the plastid NADH dehydrogenase-like complex (NDH) complex may permit loss of the plastid ndh gene suite in photoautotrophs like saguaro. Loss of these genes may be a recurring mechanism for overall plastid genome size reduction, especially in combination with loss of the IR.
Methods: Using next-generation sequence data, we assembled the plastid genome of saguaro cactus and probed the nuclear genome for transferred plastid genes and functionally related nuclear genes. We combined these results with available data across Cactaceae and seed plants more broadly to infer the history of gene loss and to assess the strength of phylogenetic association between gene loss and loss of the inverted repeat (IR).
Key results: The saguaro plastid genome is the smallest known for an obligately photosynthetic angiosperm (∼113 kb), having lost the IR and plastid ndh genes. This loss supports a statistically strong association across seed plants between the loss of ndh genes and the loss of the IR. Many nonplastid copies of plastid ndh genes were found in the nuclear genome, but none had intact reading frames; nor did three related nuclear-encoded subunits. However, nuclear pgr5, which functions in a partially redundant pathway, was intact.
Conclusions: The existence of an alternative pathway redundant with the function of the plastid NADH dehydrogenase-like complex (NDH) complex may permit loss of the plastid ndh gene suite in photoautotrophs like saguaro. Loss of these genes may be a recurring mechanism for overall plastid genome size reduction, especially in combination with loss of the IR.
ContributorsSanderson, Michael J. (Author) / Copetti, Dario (Author) / Burquez, Alberto (Author) / Bustamante, Enriquena (Author) / Charboneau, Joseph L. M. (Author) / Eguiarte, Luis E. (Author) / Kumar, Sudhir (Author) / Lee, Hyun Oh (Author) / Lee, Junki (Author) / McMahon, Michelle (Author) / Steele, Kelly (Author) / Wing, Rod (Author) / Yang, Tae-Jin (Author) / Zwickl, Derrick (Author) / Wojciechowski, Martin (Author) / College of Integrative Sciences and Arts (Contributor) / College of Liberal Arts and Sciences (Contributor) / School of Life Sciences (Contributor)
Created2015-07-01
Description
Sustainable purchasing has become and increasingly salient way by which local governments can decrease their resource consumptions, while also addressing broader climate action goals. Successfully implemented sustainable purchasing policies have the potential to reduce consumption and waste, expand green purchasing markets, and catalyze spillover benefits such as financial savings. Furthermore, city-level actions have become increasingly significant as the federal government ceases critical climate research and pulls out of collaborative climate deals (i.e. The Paris Climate Accord). Using data from the Sustainable Purchasing Researching Initiative at Arizona State University’s Center for Organization Research and Design, as well as qualitative policy analyses, the author investigates the elements of a city’s sustainable purchasing policy (SPP) that are related to its implementation success. Furthermore, the author compares these initial findings to the case study of Phoenix, AZ where she explores whether these elements are also present in the City of Phoenix’s sustainable purchasing policy. The author finds that six key policy elements are generally associated with higher SPP implementation success rates — mandatory requirements, accountability, multi-level governance, vendors requirements, advocacy, and continual improvement. While additional policy elements undoubtedly play a role in the successful implementation of a SPP, the author concludes cities that incorporate these specific elements are better positioned for successful and sustainable implementation. Conclusions further show that the City of Phoenix’s 2007 EPP contained only two of these policy elements. As a result of this project and the author’s work with the City, the 2017 revised SPP incorporates all six policy elements.
ContributorsBurwell, Caitlin (Author) / Darnall, Nicole (Contributor) / Schoon, Michael (Contributor)
Created2017-12-01