Gene Structure and Function
Shyu, Shin-Yi , Hu, Jer-Ming .
Studies of plastid 16S rDNA suggest that the evolutionary rates vary among nonphotosynthetic plants.
NONPHOTOSYNTHETIC plants usually retain a reduced plastid genome, although most of the photosynthesis-related genes are lost or become pseudogenes. In order to elucidate the plastid genome evolution in non-photosynthetic plants, we examined plastid-derived 16S rDNAs of nine nonphotosynthetic plants, including some with partial photosynthetic ability. The 16S rDNA sequences from all examined taxa were included in a phylogenetic analysis with other land plants and green algae to show their relationships. To evaluate rate heterogeneity among various 16S rDNA sequences, a relative rate tests was conducted. Compared with other angiosperms, the 16S rDNA sequences show an increasing substitution rates in four nonphotosynthetic species: Balanophora laxiflora, Mitrastemon kanehirai, Cheilotheca humilis and Cheilotheca macrocarpa. However the other five species, Aeginetia indica, Cassytha filiformi, Cuscuta australis, Galeola lindleyana, and Orobanche coerulescens, exhibited only slightly higher rates relative to most angiosperms. Some of the high sequence divergences are accompanied by an increase in A+T content of the sequences, especially in M. kanehirai, which has the highest rate among the examined taxa. In species with higher evolutionary rates of 16S rDNAs, B. laxiflora, M. kanehirai are holoparasites and C. humilis, C. macrocarpa are mycoheterotrophs. Theses plants have completely lost their photosynthetic ability. However, among the other five species examined, C. filiformi is a hemiparasitic plant and can photosynthesize itself; G. lindleyana and young stage of C. australis are slight green and maybe retain some photosynthetic ability. Although A. indica and O. coerulescens are holoparasitc plants, Orobanchaceae parasites lost their photosynthetic ability recently, and may not have enough time to accumulate variations.
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1 - National Taiwan University, Institute of Ecology and Evolutionary Biology, Rm1227, Life Science Building, 1 Roosevelt Road, Sect.4, Taipei, 106, Taiwan
rDNA and plastid sequence data.
Presentation Type: Poster:Posters for Topics
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM