title: Molecular evolution of two  consecutive carotenoid cleavage dioxygenase genes in strigolactone biosynthesis  in plants.
abstract: Strigolactones  are newly discovered plant hormones that perform various functions, from  signaling in symbiotic interactions with arbuscular mycorrhizal fungi to  controlling outgrowth of axillary buds. We examined the phylogenetic  relationships of two carotenoid cleavage dioxygenase genes (CCD7 and CCD8)  that are involved in consecutive upstream steps of the proposed strigolactone  biosynthesis pathway. The CCD7 and CCD8 sequences from 11 model  species, divided into two clades, correspond to sequences from monocotyledons  and dicotyledons. However, the sequences from the primitive moss, Physcomitrella  patens, appeared to be evolutionarily distinct from those of the  angiosperms. CCD7 and CCD8 are much conserved, since no  significant positive selection was detected among these plants. Ks values  indicated that CCD7 and CCD8 diverged about 290 to 430 million  years ago. As essential genes in the strigolactone pathway, the divergence  timing of the conserved CCD7 and CCD8 genes reflects the  approximate time of generation of strigolactone as a regulatory substance. This  timing calculation also coincides with initiation of symbiosis between plants  and microorganisms, inferred from the fossil record. Molecular evolution  analyses of genes in metabolic pathways can provide insight concerning gene  evolution.
authors.affiliation: National Key Laboratory for Crop Genetics and Germplasm Enhancement, National Center for Soybean Improvement, Soybean Research Institute, Nanjing Agricultural University, Nanjing, PR China.
authors.forename: R K
authors.initials: RK
authors.lastname: Wang
authors.forename: J J
authors.initials: JJ
authors.lastname: Lu
authors.forename: G N
authors.initials: GN
authors.lastname: Xing
authors.forename: J Y
authors.initials: JY
authors.lastname: Gai
authors.forename: T J
authors.initials: TJ
authors.lastname: Zhao
mesh_terms: D001483:Base Sequence; D002338:Carotenoids / Q000378:metabolism*; D049308:Dioxygenases / Q000235:genetics*; D019143:Evolution, Molecular; D005091:Exons / Q000235:genetics; D017343:Genes, Plant / Q000235:genetics*; D014644:Genetic Variation; D007438:Introns / Q000235:genetics; D007783:Lactones / Q000378:metabolism*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000201:enzymology* / Q000235:genetics*; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D013729:Terpenes / Q000378:metabolism*; D013997:Time Factors
chemical_list: D007783:Lactones; D010940:Plant Proteins; D013729:Terpenes; D002338:Carotenoids; D049308:Dioxygenases