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Sequencing and analysis of plastid genome in mycoheterotrophic orchid Neottia nidus-avis.

ABSTRACT: Plastids are the semiautonomous organelles that possess their own genome inherited from the cyanobacterial ancestor. The primary function of plastids is photosynthesis so the structure and evolution of plastid genomes are extensively studied in photosynthetic plants. In contrast, little is known about the plastomes of nonphotosynthetic species. In higher plants, plastid genome sequences are available for only three strictly nonphotosynthetic species, the liverwort Aneura mirabilis and two flowering plants, Epifagus virginiana and Rhizanthella gardneri. We report here the complete sequence of a plastid genome of nonphotosynthetic mycoheterotrophic orchid Neottia nidus-avis, determined using 454 pyrosequencing technology. It was found to be reduced in both genome size and gene content; this reduction is however not as drastic as in the other nonphotosynthetic orchid, R. gardneri. Neottia plastome lacks all genes encoding photosynthetic proteins, RNA polymerase subunits but retains most genes of translational apparatus. Those genes that are retained have an increased rate of both synonymous and nonsynonymous substitutions but do not exhibit relaxation of purifying selection either in Neottia or in Rhizanthella.

SUBMITTER: Logacheva MD

PROVIDER: S-EPMC3228488 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Sequencing and analysis of plastid genome in mycoheterotrophic orchid Neottia nidus-avis.

Logacheva Maria D MD Schelkunov Mikhail I MI Penin Aleksey A AA

Genome biology and evolution 20111004

Plastids are the semiautonomous organelles that possess their own genome inherited from the cyanobacterial ancestor. The primary function of plastids is photosynthesis so the structure and evolution of plastid genomes are extensively studied in photosynthetic plants. In contrast, little is known about the plastomes of nonphotosynthetic species. In higher plants, plastid genome sequences are available for only three strictly nonphotosynthetic species, the liverwort Aneura mirabilis and two flower ...[more]

PMID: 21971517

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Project description:Background and aimsDespite their significant capacity to propagate vegetatively, most orchids reproduce via seeds. Sexual reproduction via seed is commonly reported, in contrast to apomixis, whereby seeds are clones of the mother. Although insect pollination and autonomous self-pollination exist in mycoheterotrophic plants, the reproductive embryology of these plants remains under-studied. This paper provides evidence for the co-occurrence of both sexual and apomictic reproduction in a population of mycoheterotrophic plants - Epipogium aphyllum We investigated seed formation via open pollination, induced autogamy, autogamy sensu stricto and autonomous apomixis.MethodsThe study was performed on a population of E. aphyllum located in northern Poland. The research included studies of the micromorphology, histochemistry and embryology of four types of reproductive systems. Scanning, fluorescence and light microscopy accompanied by graphical and statistical analyses were employed.Key resultsWe observed gametophyte development, from the one-nucleate stage to maturity, in unpollinated flower buds. The lack of zygotes in flower buds indicated that fertilization did not occur at this stage. Manual self-pollination led to a zygote, followed by embryo formation. Fertilization and embryo development derived from embryogenesis via open pollination is delayed compared with hand pollination. Isolation from external pollination resulted only in structures resembling zygotes that may originate either sexually or independent of fertilization. Parthenogenetic structures that resembled zygotes were observed in flowers that were emasculated and isolated from pollination. Zygotes formed at significantly higher frequencies via open pollination and induced autogamy in comparison to the parthenogenetic structures formed in other treatments.ConclusionsWe showed the absence of pre-zygotic barriers for autogamy in E. aphyllum Self-pollination and self-fertilization are possible; however, natural self-pollination is unlikely or rare due to the position of the pollinia. Incidental parthenogenesis in E. aphyllum is very likely, given the biology of ovule development of this mycoheterotrophic orchid. This species therefore has the potential to produce seeds via both sexual and asexual means, although the contribution of apomixis to this process appears largely negligible.

Dataset Information

Sequencing and analysis of plastid genome in mycoheterotrophic orchid Neottia nidus-avis.

Publications

Sequencing and analysis of plastid genome in mycoheterotrophic orchid Neottia nidus-avis.

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