Tansley Review No. 116

N., A.; Söderbäck, Erik; Bergman, Birgitta

doi:10.1046/j.1469-8137.2000.00720.x

Cited by 308 publications

(56 citation statements)

References 292 publications

(316 reference statements)

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“…Overall, DDN released from internal symbionts should be easier and faster accessible to the coral host as compared to DDN released from external symbionts. This has been previously shown for terrestrial plant-diazotroph symbioses in which DDN release by diazotrophs and uptake by the host occurs at interfaces where both partner are in close contact to each other (Rai et al, 2000). conditions.…”

Section: Mechanisms Of Ddn Uptake and Transfer Among Compartments Of supporting

confidence: 64%

“…However, the exact mechanisms of release and uptake remain unexplored also for plant-diazotroph symbioses, but many of the interface membranes of both partners possess H + -ATPase, implying the presence of transport systems (Rai et al, 2000). Using multi-isotope imaging mass spectrometry Lechene et al (2007) imaged and measured N 2 fixation by endosymbiotic diazotrophs associated with shipworms.…”

Section: Mechanisms Of Ddn Uptake and Transfer Among Compartments Of mentioning

confidence: 99%

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Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

2017

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Coral reefs are highly productive ecosystems thriving in nutrient-poor waters. Their productivity depends largely on the availability of nitrogen, the proximate limiting nutrient for primary production. In reefs, the major nitrogen pathways include regeneration, nitrification, ammonification and dinitrogen (N 2 ) fixation. N 2 fixation is performed by prokaryotes called "diazotrophs" that abound in coral rubbles, sandy bottoms, microbial mats, or seagrass meadows. Corals, which are the main reef builders, have developed a partnership with dinoflagellates which transform dissolved inorganic nitrogen into amino acids and protein, and with diazotrophs to gain diazotrophically-derived nitrogen (DDN). Pioneering studies found active diazotrophic cyanobacteria in the corals' mucus and/or tissue, and later high throughput sequencing efforts have described diverse communities of non-cyanobacterial diazotrophs associated with scleractinian corals. Yet, the metabolic processes behind these associations and how they benefit corals are currently not well understood. While genomic studies describe the diversity of diazotrophs and isotopic tracer experiments quantify N 2 fixation rates, combined advanced methods are needed to elucidate the mechanisms behind the transfer of DDN to the coral holobiont and whether these mechanisms change according to the identity of the diazotrophs or coral species. Here we review our current knowledge on N 2 fixation in corals: the diversity and localization of diazotrophs in the coral holobiont, the environmental factors controlling N 2 fixation, the fate of DDN within the coral symbiosis as well as its potential role in coral resilience. We finally summarize the unknowns: are the diversity, abundance and localization of diazotrophs within the holobiont species-and/or site-specific? Do they have an impact on DDN production? What are the metabolic mechanisms implicated? Do they change spatially, temporally or according to environmental factors? We encourage scientists to undertake research efforts to tackle these questions in order to shed light on nitrogen cycling in reef ecosystems and to understand if coral-associated N 2 fixation can improve coral's resilience in the face of climate change.

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Section: Mechanisms Of Ddn Uptake and Transfer Among Compartments Of supporting

confidence: 64%

Section: Mechanisms Of Ddn Uptake and Transfer Among Compartments Of mentioning

confidence: 99%

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

2017

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“…It has been shown that nitrogen deprivation stimulates modern symbiotic associations [86,90] and that nitrogenrich conditions on the contrary facilitate the dissipation of pre-established symbiotic relationships [86]. If nitrogen was the key factor for the host and symbiont to form the initial association, it is congruent with the finding that present-day members of filamentous, heterocyst-forming and N 2 -fixing cyanobacterial sections IV and V have a collection of genes most similar to that possessed by the plastid ancestor [39,46].…”

Section: Plastid Origin and The Origin Of Oxygenic Photosynthesismentioning

confidence: 99%

“…In nature, highly diverse taxonomic hosts form symbiotic or endosymbiotic associations with photosynthesizing and N 2 -fixing cyanobacteria in various environments. They range from autotrophic algae and plants [86] to heterotrophic fungi where over 1500 species represent cases of lichen symbioses with cyanobacteria [87]. Specifically in plants, cyanobacterial symbioses are present in the four main groups -gymnosperms, angiosperms, pteridophytes and bryophytes [86].…”

Section: Why: the Physiological Context Of Plastid Originmentioning

confidence: 99%

“…Another example is the angiosperm Gunnera manicata that uses the nitrogen provided by the filamentous symbiont (Nostoc punctiforme) and continues growing under N-limited conditions in the presence of the symbiont [90]. In gymnosperms, a nitrogen-fixing cyanobacterial symbiont (Nostoc) was found in the roots of most known cycad species [91,92].It has been shown that nitrogen deprivation stimulates modern symbiotic associations [86,90] and that nitrogenrich conditions on the contrary facilitate the dissipation of pre-established symbiotic relationships [86]. If nitrogen was the key factor for the host and symbiont to form the initial association, it is congruent with the finding that present-day members of filamentous, heterocyst-forming and N 2 -fixing cyanobacterial sections IV and V have a collection of genes most similar to that possessed by the plastid ancestor [39,46].…”

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Plastid origin: who, when and why?

Roettger

Zimorski

et al. 2014

Acta Soc Bot Pol

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Plastid origin: 110 years since MereschkowskyPlastids are eukaryotic metabolic compartments responsible for photosynthesis [1] and a variety of metabolic functions including the biosynthesis of amino acids [2], nucleotides [3], lipids [4], and cofactors [5]. The importance of plastids to photosynthetic lineages of eukaryotes cannot be overstated. In 1905, Mereschkowsky proposed a fully articulated version of endosymbiotic theory positing that plastids originated from cyanobacteria that came to reside as symbionts in eukaryotic cells [6,7]. The theory did not make its way into mainstream biological thinking until it was revived in a synthesis by Margulis [8,9] that also incorporated Wallin's [10] -and Paul Portier's (published in French, cited in Sapp [11]) -ideas about endosymbiotic theory for mitochondrial origin, yet adorned by Margulis' own suggestion of a spirochaete origin of flagella. The spirochaete story never took hold, leaving endosymbiotic theory with three main players: the plastid, the mitochondrion, and its host, which is now understood to be an archaeon [12]. Well into the 1970s, resistance to the concept of endosymbiosis for the origin of plastids (and mitochondria) was stiff [13][14][15].With the availability of protein and DNA sequences, of which Mereschkowsky knew nothing, strong evidence had accumulated by the early 1980s that plastids originated through endosymbiosis from cyanobacteria, rather than autogenously [16]. However, there have been recurrent suggestions, starting with Mereschkowsky [6] and tracing into the 1970's [17], that there were several independent origins of plastids from cyanobacteria. Today it is widely, but not universally [18,19], accepted that plastids had a single origin. The strongest evidence for that view is that the protein import machinery, a good marker for endosymbiotic events [20], in the three lineages of Archaeplastida -eukaryotes with primary plastids [21] -consists of homologous host-originated components [22][23][24], which would not be the case had plastids in those lineages arisen from independent cyanobacterial symbioses.Genomics has enriched our understanding of plastid origin. We now know that the plastid genome has undergone extreme reduction while leaving its imprints in the nuclear genome through endosymbiotic gene transfer [25,26] and that plastids have spread across eukaryotes through symbiosis and become secondary and tertiary plastids [27]. Genomic data also supports the case for a single plastid origin. Despite some concerns about incomplete sampling and phylogenetic artifacts [18], recent analyses from different groups, incorporating improved phylogenetic algorithms and sampling of cyanobacteria, provide two lines of evidence, in addition to * Corresponding author. Email: bill@hhu.deHandling Editor: Andrzej Bodył INVITED REVIEW Acta Soc Bot Pol 83(4): 281-289 DOI: 10.5586/asbp.2014.045 Received: 2014-11-20 Accepted: 2014-12-04 Published electronically: 2014 Plastid origin: who, when and why?Chuan Ku, Mayo Roettger, Verena Zimorski, Shijulal...

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