title: Origin and mechanism of crassulacean acid metabolism in orchids as implied by comparative transcriptomics and genomics of the carbon fixation pathway.
abstract: Crassulacean acid metabolism (CAM) is a CO2 fixation pathway that maximizes water-use efficiency (WUE), compared with the C3/C4 CO2 pathway, which permits CAM plants to adapt to arid environments. The CAM pathway provides excellent opportunities to genetically design plants, especially bioenergy crops, with a high WUE and better photosynthetic performance than C3/C4 in arid environments. The information available on the origin and evolution of CAM is scant, however. Here, we analyzed transcriptomes from 13 orchid species and two existing orchid genomes, covering CAM and C3 plants, with an emphasis on comparing 13 gene families involved in the complete carbon fixation pathway. The dosage of the core photosynthesis-related genes plays no substantial role in the evolution of CAM in orchids; however, CAM may have evolved primarily by changes at the transcription level of key carbon fixation pathway genes. We proposed that in both dark and light, CO2 is primarily fixed and then released through two metabolic pathways via known genes, such as PPC1, PPDK and PPCK. This study reports a comprehensive comparison of carbon fixation pathway genes across different photosynthetic plants, and reveals the importance of the level of expression of key genes in the origin and evolution of CAM.
authors.affiliation: Center for Genomics and Biotechnology, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
authors.forename: Liangsheng
authors.identifier: http://orcid.org/0000-0003-1919-3677
authors.initials: L
authors.lastname: Zhang
authors.affiliation: College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China.|Department of Plant Sciences, The University of Tennessee, Knoxville, TN, 37996, USA.
authors.forename: Fei
authors.identifier: http://orcid.org/0000-0002-4346-6906
authors.initials: F
authors.lastname: Chen
authors.affiliation: Shenzhen Key Laboratory for Orchid Conservation and Utilization, The National Orchid Conservation Center of China and The Orchid Conservation & Research Center of Shenzhen, Shenzhen, 518114, China.
authors.forename: Guo-Qiang
authors.initials: GQ
authors.lastname: Zhang
authors.affiliation: Shenzhen Key Laboratory for Orchid Conservation and Utilization, The National Orchid Conservation Center of China and The Orchid Conservation & Research Center of Shenzhen, Shenzhen, 518114, China.
authors.forename: Yong-Qiang
authors.initials: YQ
authors.lastname: Zhang
authors.affiliation: Shenzhen Key Laboratory for Orchid Conservation and Utilization, The National Orchid Conservation Center of China and The Orchid Conservation & Research Center of Shenzhen, Shenzhen, 518114, China.
authors.forename: Shance
authors.initials: S
authors.lastname: Niu
authors.affiliation: College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China.|Department of Plant Sciences, The University of Tennessee, Knoxville, TN, 37996, USA.
authors.forename: Jin-Song
authors.initials: JS
authors.lastname: Xiong
authors.affiliation: Department of Biology, Saint Louis University, St Louis, MO, 63103, USA.
authors.forename: Zhenguo
authors.initials: Z
authors.lastname: Lin
authors.affiliation: College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China.|Department of Plant Sciences, The University of Tennessee, Knoxville, TN, 37996, USA.
authors.forename: Zong-Ming Max
authors.initials: ZM
authors.lastname: Cheng
authors.affiliation: Shenzhen Key Laboratory for Orchid Conservation and Utilization, The National Orchid Conservation Center of China and The Orchid Conservation & Research Center of Shenzhen, Shenzhen, 518114, China.
authors.forename: Zhong-Jian
authors.initials: ZJ
authors.lastname: Liu
mesh_terms: D057486:Carbon Cycle; D019143:Evolution, Molecular; D017343:Genes, Plant; D029595:Orchidaceae / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D054046:Plant Stomata / Q000378:metabolism; D059467:Transcriptome
keywords: Orchidaceae; carbon fixation; crassulacean acid metabolism (CAM); gene family; photosynthesis; transcriptome