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Red algae lose key mitochondrial genes in response to becoming parasitic.

ABSTRACT: Red algal parasites are unusual because the vast majority of them parasitize species with which they share a recent common ancestor. This strategy has earned them the name "adelphoparasites," from the Greek, adelpho, meaning "kin." Intracellular adelphoparasites are very rare in nature, yet have independently evolved hundreds of times among the floridiophyte red algae. Much is known about the life history and infection cycle of these parasites but nearly nothing in known about their genomes. We sequenced the mitochondrial genomes of the free-living Gracilariopsis andersonii and its closely related parasite Gracilariophila oryzoides to determine what effect a parasitic lifestyle has on the genomes of red algal parasites. Whereas the parasite genome is similar to the host in many ways, the genes encoding essential proteins ATP8 and SDHC are pseudogenes in the parasite. The mitochondrial genome of parasite from a different class of red algae, Plocamiocolax puvinata, has lost the atp8 gene entirely, indicating that this gene is no longer critical in red algal parasite mitochondria.

SUBMITTER: Hancock L

PROVIDER: S-EPMC3014286 | biostudies-literature | 2010

REPOSITORIES: biostudies-literature

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Red algae lose key mitochondrial genes in response to becoming parasitic.

Hancock Lillian L Goff Lynda L Lane Christopher C

Genome biology and evolution 20101115

Red algal parasites are unusual because the vast majority of them parasitize species with which they share a recent common ancestor. This strategy has earned them the name "adelphoparasites," from the Greek, adelpho, meaning "kin." Intracellular adelphoparasites are very rare in nature, yet have independently evolved hundreds of times among the floridiophyte red algae. Much is known about the life history and infection cycle of these parasites but nearly nothing in known about their genomes. We ...[more]

PMID: 21081313

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Project description:Horizontal gene transfer (HGT) is relatively common in plant mitochondrial genomes but the mechanisms, extent and consequences of transfer remain largely unknown. Previous results indicate that parasitic plants are often involved as either transfer donors or recipients, suggesting that direct contact between parasite and host facilitates genetic transfer among plants.In order to uncover the mechanistic details of plant-to-plant HGT, the extent and evolutionary fate of transfer was investigated between two groups: the parasitic genus Cuscuta and a small clade of Plantago species. A broad polymerase chain reaction (PCR) survey of mitochondrial genes revealed that at least three genes (atp1, atp6 and matR) were recently transferred from Cuscuta to Plantago. Quantitative PCR assays show that these three genes have a mitochondrial location in the one species line of Plantago examined. Patterns of sequence evolution suggest that these foreign genes degraded into pseudogenes shortly after transfer and reverse transcription (RT)-PCR analyses demonstrate that none are detectably transcribed. Three cases of gene conversion were detected between native and foreign copies of the atp1 gene. The identical phylogenetic distribution of the three foreign genes within Plantago and the retention of cytidines at ancestral positions of RNA editing indicate that these genes were probably acquired via a single, DNA-mediated transfer event. However, samplings of multiple individuals from two of the three species in the recipient Plantago clade revealed complex and perplexing phylogenetic discrepancies and patterns of sequence divergence for all three of the foreign genes.This study reports the best evidence to date that multiple mitochondrial genes can be transferred via a single HGT event and that transfer occurred via a strictly DNA-level intermediate. The discovery of gene conversion between co-resident foreign and native mitochondrial copies suggests that transferred genes may be evolutionarily important in generating mitochondrial genetic diversity. Finally, the complex relationships within each lineage of transferred genes imply a surprisingly complicated history of these genes in Plantago subsequent to their acquisition via HGT and this history probably involves some combination of additional transfers (including intracellular transfer), gene duplication, differential loss and mutation-rate variation. Unravelling this history will probably require sequencing multiple mitochondrial and nuclear genomes from Plantago. See Commentary: http://www.biomedcentral.com/1741-7007/8/147.

Project description:BackgroundRed coralline algae are critical components of tropical reef systems, and their success and development is, at least in part, dependent on photosynthesis. However, natural variability in the photosynthetic characteristics of red coralline algae is poorly understood. This study investigated diurnal variability in encrusting Porolithon sp. and free-living Lithophyllum kotschyanum. Measured parameters included: photosynthetic characteristics, pigment composition, thallus reflectance and intracellular concentrations of dimethylsulphoniopropionate (DMSP), an algal antioxidant that is derived from methionine, an indirect product of photosynthesis. L. kotschyanum thalli were characterised by a bleached topside and a pigmented underside.ResultsMinimum saturation intensity and intracellular DMSP concentrations in Porolithon sp. were characterised by significant diurnal patterns in response to the high-light regime. A smaller diurnal pattern in minimum saturation intensity in the topside of L. kotschyanum was also evident. The overall reflectance of the topside of L. kotschyanum also exhibited a diurnal pattern, becoming increasingly reflective with increasing ambient irradiance. The underside of L. kotschyanum, which is shaded from ambient light exposure, exhibited a much smaller diurnal variability.ConclusionsThis study highlights a number of dynamic photoinhibition strategies adopted by coralline algae, enabling them to tolerate, rather than be inhibited by, the naturally high irradiance of tropical reef systems; a factor that may become more important in the future under global change projections. In this context, this research has significant implications for tropical reef management planning and conservation monitoring, which, if natural variability is not taken into account, may become flawed. The information provided by this research may be used to inform future investigations into the contribution of coralline algae to reef accretion, ecosystem service provision and palaeoenvironmental reconstruction.

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Red algae lose key mitochondrial genes in response to becoming parasitic.

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Red algae lose key mitochondrial genes in response to becoming parasitic.

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