Genome rearrangements during Anabaena heterocyst differentiation

The filamentous cyanobacterium Anabaena sp. PCC 7120 produces specialized, terminally differentiated cells called heterocysts that are the sites of nitrogen fixation. The genome of Anabaena undergoes at least two specific developmentally regulated DNA rearrangements during heterocyst differentiation. One rearrangement involves the nitrogen-fixation genes nifH, nifD, and nifK. During heterocyst differentiation, an 11-kilobase (kb) DNA element is excised from the 3′ coding region of the nifD gene by site-specific recombination within 11 base pair, directly repeated sequences present at the ends of the element. The excision results in formation of a complete nifD coding sequence and allows transcription of all three genes from a single promoter upstream of nifH. The gene xisA, located at one end of the 11-kb element, is believed to encode the site-specific recombinase responsible for excision of the element from the nifD gene. A second DNA rearrangement occurs close to the 5′ end of the nifS gene and results in placing the genes rbcL and rbcS approximately 10 kb from the nif gene cluster. This rearrangement is also a deletion from the chromosome but involves a significantly larger segment of the genome, 55 kb. The genomic breakpoints of the nifS rearrangement have been cloned and sequenced. The recombination sites show no homology to those involved in the nifD rearrangement. This suggests that each rearrangement is catalyzed by a different site-specific recombination system and that the two arrangements may be independently regulated.

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Rearrangement of nif genes during cyanobacterial heterocyst differentiation

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1987.0055 ◽

1987 ◽

Vol 317 (1184) ◽

pp. 173-181 ◽

Cited By ~ 7

Keyword(s):

Dna Sequences ◽

Transcription Unit ◽

Gene Arrangement ◽

Filamentous Cyanobacterium ◽

Gene Encoding ◽

Α Subunit ◽

Site Specific ◽

Heterocyst Differentiation ◽

Site Specific Recombination ◽

Recombination System

Anabaena is a filamentous cyanobacterium that produces specialized cells, called heterocysts, at regular intervals along each filament when deprived of fixed nitrogen under aerobic conditions. Heterocysts are anaerobic factories for nitrogen fixation. In Anabaena vegetative-cell DNA, the nifD gene, encoding the α subunit of nitrogenase, is interrupted by an 11 000 base pair DNA element. During the differentiation of heterocysts from vegetative cells, this 11 kilobase (kb) element is excised by site-specific recombination between short, directly repeated DNA sequences present at the ends of the element. The excision results in restoration of the nifD coding sequence and of the entire nifHDK transcription unit. A gene has been identified, within the 11 kb element, that is believed to encode the site-specific recombinase responsible for excision of the element during heterocyst differentiation. A second developmentally regulated gene arrangement has also been observed in Anabaena . This event occurs close to the nifS gene and involves a different set of repeated sequences, implying a different site-specific recombination system.

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The CRP-family transcriptional regulator DevH regulates expression of heterocyst-specific genes at the later stage of differentiation in the cyanobacterium Anabaena sp. strain PCC 7120

10.1101/2020.04.22.054668 ◽

2020 ◽

Author(s):

Yohei Kurio ◽

Yosuke Koike ◽

Yu Kanesaki ◽

Satoru Watanabe ◽

Shigeki Ehira

Keyword(s):

Nitrogen Fixation ◽

Gene Cluster ◽

Transcriptional Regulator ◽

Heterocyst Differentiation ◽

Differentiated Cells ◽

Cyanobacterium Anabaena ◽

Anabaena Sp ◽

Oxygen Evolving ◽

Pcc 7120 ◽

Polysaccharide Layer

SummaryHeterocysts are terminally differentiated cells of filamentous cyanobacteria, which are specialized for nitrogen fixation. Because nitrogenase, an enzyme for nitrogen fixation, is easily inactivated by oxygen, the intracellular environment of heterocysts is kept microoxic. In heterocysts, the oxygen-evolving photosystem II is inactivated, a heterocyst-specific envelope with an outer polysaccharide layer and an inner glycolipid layer is formed to limit oxygen entry, and oxygen consumption is activated. Heterocyst differentiation, which is accompanied by drastic morphological and physiological changes, requires strictly controlled gene expression systems. Here, we investigated the functions of a CRP-family transcriptional regulator, DevH, in the process of heterocyst differentiation. A devH-knockdown strain, devHKD, was created by replacing the original promoter with the gifA promoter, which is repressed during heterocyst differentiation. Although devHKD formed morphologically distinct cells with the heterocyst envelope polysaccharide layer, it was unable to grow diazotrophically. Genes involved in construction of the microoxic environment, such as cox operons and the hgl island, were not upregulated in devHKD. Moreover, expression of the nif gene cluster was completely abolished. Even under anaerobic conditions, the nif gene cluster was not induced in devHKD. Thus, DevH is necessary for the establishment of a microoxic environment and induction of nitrogenase in heterocysts.

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Effect on Heterocyst Differentiation of Nitrogen Fixation in Vegetative Cells of the Cyanobacterium Anabaena variabilisATCC 29413

Journal of Bacteriology ◽

10.1128/jb.183.1.280-286.2001 ◽

2001 ◽

Vol 183 (1) ◽

pp. 280-286 ◽

Cited By ~ 58

Author(s):

Teresa Thiel ◽

Brenda Pratte

Keyword(s):

Nitrogen Fixation ◽

Wild Type Strain ◽

Regulatory Protein ◽

Growth Conditions ◽

Vegetative Cells ◽

Heterocyst Differentiation ◽

Anoxic Conditions ◽

Differentiated Cells ◽

Cyanobacterium Anabaena

ABSTRACT Heterocysts are terminally differentiated cells of some filamentous cyanobacteria that fix nitrogen for the entire filament under oxic growth conditions. Anabaena variabilis ATCC 29413 is unusual in that it has two Mo-dependent nitrogenases; one, called Nif1, functions in heterocysts, while the second, Nif2, functions under anoxic conditions in vegetative cells. Both nitrogenases depended on expression of the global regulatory protein NtcA. It has long been thought that a product of nitrogen fixation in heterocysts plays a role in maintenance of the spaced pattern of heterocyst differentiation. This model assumes that each cell in a filament senses its own environment in terms of nitrogen sufficiency and responds accordingly in terms of differentiation. Expression of the Nif2 nitrogenase under anoxic conditions in vegetative cells was sufficient to support long-term growth of a nif1 mutant; however, that expression did not prevent differentiation of heterocysts and expression of thenif1 nitrogenase in either the nif1 mutant or the wild-type strain. This suggested that the nitrogen sufficiency of individual cells in the filament did not affect the signal that induces heterocyst differentiation. Perhaps there is a global mechanism by which the filament senses nitrogen sufficiency or insufficiency based on the external availability of fixed nitrogen. The filament would then respond by producing heterocyst differentiation signals that affect the entire filament. This does not preclude cell-to-cell signaling in the maintenance of heterocyst pattern but suggests that overall control of the process is not controlled by nitrogen insufficiency of individual cells.

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Gene insertion and replacement in Schizosaccharomyces pombe mediated by the Streptomyces bacteriophage φC31 site-specific recombination system

Molecular Genetics and Genomics ◽

10.1007/s004380100498 ◽

2001 ◽

Vol 265 (6) ◽

pp. 1031-1038 ◽

Cited By ~ 59

Author(s):

L. Thomason ◽

R. Calendar ◽

D. Ow

Keyword(s):

Schizosaccharomyces Pombe ◽

Site Specific ◽

Site Specific Recombination ◽

Gene Insertion ◽

Recombination System ◽

Site Specific Recombination System

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Vika/vox, a novel efficient and specific Cre/loxP-like site-specific recombination system

Nucleic Acids Research ◽

10.1093/nar/gks1037 ◽

2012 ◽

Vol 41 (2) ◽

pp. e37-e37 ◽

Cited By ~ 24

Author(s):

Madina Karimova ◽

Josephine Abi-Ghanem ◽

Nicolas Berger ◽

Vineeth Surendranath ◽

Maria Teresa Pisabarro ◽

...

Keyword(s):

Site Specific ◽

Site Specific Recombination ◽

Recombination System ◽

Site Specific Recombination System

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Manipulation of Pattern of Cell Differentiation in a hetR Mutant of Anabaena sp. PCC 7120 by Overexpressing hetZ Alone or with hetP

Life ◽

10.3390/life8040060 ◽

2018 ◽

Vol 8 (4) ◽

pp. 60 ◽

Cited By ~ 5

Author(s):

He Zhang ◽

Xudong Xu

Keyword(s):

Cell Differentiation ◽

Peptide Inhibitor ◽

Filamentous Cyanobacterium ◽

Heterocyst Differentiation ◽

Cyanobacterium Anabaena ◽

Anabaena Sp ◽

Pcc 7120

In the filamentous cyanobacterium, Anabaena sp. PCC 7120, single heterocysts differentiate at semi-regular intervals in response to nitrogen stepdown. HetR is a principal regulator of heterocyst differentiation, and hetP and hetZ are two genes that are regulated directly by HetR. In a hetR mutant generated from the IHB (Institute of Hydrobiology) substrain of PCC 7120, heterocyst formation can be restored by moderate expression of hetZ and hetP. The resulting heterocysts are located at terminal positions. We used a tandem promoter, PrbcLPpetE, to express hetZ and hetP strongly in the hetR mutant. Co-expression of hetZ and hetP enabled the hetR mutant to form multiple contiguous heterocysts at both terminal and intercalary positions. Expression of hetZ, alone resulted in terminally located heterocysts, whereas expression of hetP, alone produced enlarged cells in strings. In the absence of HetR, formation of heterocysts was insensitive to the peptide inhibitor, RGSGR.

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