Evidence of a chimeric genome in the cyanobacterial ancestor of plastids

Background

Horizontal gene transfer (HGT) is a vexing fact of life for microbial phylogeneticists. Given the substantial rates of HGT observed in modern-day bacterial chromosomes, it is envisaged that ancient prokaryotic genomes must have been similarly chimeric. But where can one find an ancient prokaryotic genome that has maintained its ancestral condition to address this issue? An excellent candidate is the cyanobacterial endosymbiont that was harnessed over a billion years ago by a heterotrophic protist, giving rise to the plastid. Genetic remnants of the endosymbiont are still preserved in plastids as a highly reduced chromosome encoding 54 – 264 genes. These data provide an ideal target to assess genome chimericism in an ancient cyanobacterial lineage.

Results

Here we demonstrate that the origin of the plastid-encoded gene cluster for menaquinone/phylloquinone biosynthesis in the extremophilic red algae Cyanidiales contradicts a cyanobacterial genealogy. These genes are relics of an ancestral cluster related to homologs in Chlorobi/Gammaproteobacteria that we hypothesize was established by HGT in the progenitor of plastids, thus providing a 'footprint' of genome chimericism in ancient cyanobacteria. In addition to menB, four components of the original gene cluster (menF, menD, menC, and menH) are now encoded in the nuclear genome of the majority of non-Cyanidiales algae and plants as the unique tetra-gene fusion named PHYLLO. These genes are monophyletic in Plantae and chromalveolates, indicating that loci introduced by HGT into the ancestral cyanobacterium were moved over time into the host nucleus.

Conclusion

Our study provides unambiguous evidence for the existence of genome chimericism in ancient cyanobacteria. In addition we show genes that originated via HGT in the cyanobacterial ancestor of the plastid made their way to the host nucleus via endosymbiotic gene transfer (EGT).

     

Setae thickening in <Emphasis Type="Italic">Daphnia magna</Emphasis> alleviates the food stress caused by the filamentous cyanobacteria

It is assumed that daphnids adjust the filter screen morphology in order to minimize the interference with cyanobacterial filaments. The aim of this study was to investigate the impact of filamentous cyanobacteria (Aphanizomenon gracile Lemmermann, Cylindrospermopsis raciborskii Woloszynska Seenaya et Subba Raju) on the thickness and length of setae of the third pair of thoracic limbs of Daphnia magna. The second objective was to assess whether the setae modifications could improve the performance of daphnids in the presence of cyanobacteria. Three clones of Daphnia magna Straus were cultured with: green algae; green algae with filaments of Cylindrospermopsis; and green algae with filaments of Aphanizomenon. The size and age of animals in the first reproduction cycle as well as the number of offspring were recorded. Setae thickness and length were measured in the central part of each endopodite. Additionally, we analyzed how the changes in setae morphology affect the fitness of experimental animals using the intrinsic rate of population increase calculated with the Euler–Lotka equation. The results showed that the thickness and length of setae increased in the presence of filamentous cyanobacteria. Moreover, cyanobacteria-induced setae thickening was positively correlated to the fitness of daphnids, which may indicate setae thickening as a phenotypic adaptation to cope with food stress caused by filamentous cyanobacteria.     

Distribution of alkaline phosphatase genes in cyanobacteria and the role of alkaline phosphatase on the acquisition of phosphorus from dissolved organic phosphorus for cyanobacterial growth

Phosphorus is a vital nutrient for cyanobacterial growth. Aside from dissolved inorganic phosphorus, dissolved organic phosphorus (DOP) is used by cyanobacterial species via the activity of alkaline phosphatase (APase), which likely plays an important role in acquiring phosphorus for algal growth in the same manner as it does in other bacteria. In this work, APase genes phoA, phoD, and phoX were found distributed in the cyanobacterial strains included in the algal genome collection of the NCBI database. PhoX has a wider distribution than the classical phoA and phoD. Furthermore, multiple types of APase genes were simultaneously identified in a single strain or genome. Anabaena flos-aquae FACHB-245 was selected as a typical strain to study the performance of cyanobacteria growing on DOP. In algal growth involving AMP or lecithin, APase regulates the release of phosphorus from DOP as confirmed by the relative quantification of phoD and phoX expression levels. Our results confirmed that the distribution of APase is prevalent in cyanobacteria and thus provides a new insight into the potential role of cyanobacterial APase on phosphorus acquisition in natural environment.     

Phylogenetic analysis of proteins involved in the stringent response in plant cells

The nucleotide (p)ppGpp is a second messenger that controls the stringent response in bacteria. The stringent response modifies expression of a large number of genes and metabolic processes and allows bacteria to survive under fluctuating environmental conditions. Recent genome sequencing analyses have revealed that genes responsible for the stringent response are also found in plants. These include (p)ppGpp synthases and hydrolases, RelA/SpoT homologs (RSHs), and the pppGpp-specific phosphatase GppA/Ppx. However, phylogenetic relationship between enzymes involved in bacterial and plant stringent responses is as yet generally unclear. Here, we investigated the origin and evolution of genes involved in the stringent response in plants. Phylogenetic analysis and primary structures of RSH homologs from different plant phyla (including Embryophyta, Charophyta, Chlorophyta, Rhodophyta and Glaucophyta) indicate that RSH gene families were introduced into plant cells by at least two independent lateral gene transfers from the bacterial Deinococcus-Thermus phylum and an unidentified bacterial phylum; alternatively, they were introduced into a proto-plant cell by a lateral gene transfer from the endosymbiotic cyanobacterium followed by gene loss of an ancestral RSH gene in the cyanobacterial linage. Phylogenetic analysis of gppA/ppx families indicated that plant gppA/ppx homologs form an individual cluster in the phylogenetic tree, and show a sister relationship with some bacterial gppA/ppx homologs. Although RSHs contain a plastidial transit peptide at the N terminus, GppA/Ppx homologs do not, suggesting that plant GppA/Ppx homologs function in the cytosol. These results reveal that a proto-plant cell obtained genes for the stringent response by lateral gene transfer events from different bacterial phyla and have utilized them to control metabolism in plastids and the cytosol.     

Effectiveness of cyanobacteria and green algae in enhancing the photosynthetic performance and growth of willow (<Emphasis Type="Italic">Salix viminalis</Emphasis> L.) plants under limited synthetic fertilizers application

The physiological response of plants to triple foliar biofertilization with cyanobacteria and green algae under the conditions of limited use of chemical fertilizers was investigated. Triple foliar biofertilization with intact cells of Microcystis aeruginosa MKR 0105, Anabaena sp. PCC 7120, and Chlorella sp. significantly enhanced physiological performance and growth of plants fertilized with a synthetic fertilizer YaraMila Complex (1.0, 0.5, and 0.0 g per plant). This biofertilization increased the stability of cytomembranes, chlorophyll content, intensity of net photosynthesis, transpiration, stomatal conductance, and decreased intercellular CO2 concentration. Applied monocultures augmented the quantity of N, P, K in plants, the activity of enzymes, such as dehydrogenases, RNase, acid or alkaline phosphatase and nitrate reductase. They also improved the growth of willow plants. This study revealed that the applied nontoxic cyanobacteria and green algae monocultures have a very useful potential to increase production of willow, and needed doses of chemical fertilizers can be reduced.     

Nitrogen-fixing cyanobacterium <Emphasis Type="Italic">Trichormus variabilis</Emphasis> of the Lake Baikal phytoplankton

A new filamentous cyanobacterial strain BAC 9610 was isolated from the lake Baikal pelagial. Data obtained by light, scanning, and transmission electron microscopy, along with 16S rRNA gene sequence analysis, allowed the bacterium identification as Trichormus variabilis, previously known as Anabaena variabilis. Trichormus is a cyanobacterial genus not presented in the list of Baikal plankton algae; A. variabilis also hasn’t been previously detected in Baikal phytoplankton. T. variabilis nitrogen fixation ability was demonstrated. The gene responsible for nitrogen fixation, nifH, was identified by PCR and was partially sequenced. No hepatotoxin synthesis genes were revealed in the strain.     

The SbcC and SbcD homologs of the cyanobacterium <Emphasis Type="Italic">Anabaena</Emphasis> sp. strain PCC7120 (Alr3988 and All4463) contribute independently to DNA repair

The ubiquitous SbcCD exonuclease complex has been shown to perform an important role in DNA repair across prokaryotes and eukaryotes. However, they have remained uncharacterized in the ancient and stress-tolerant cyanobacteria. In the cyanobacterium Anabaena sp. strain PCC7120, SbcC and SbcD homologs, defined on the basis of the presence of corresponding functional domains, are annotated as hypothetical proteins, namely Alr3988 and All4463 respectively. Unlike the presence of sbcC and sbcD genes in a bicistronic operon in most organisms, these genes were distantly placed on the chromosome in Anabaena, and found to be negatively regulated by LexA. Both the genes were found to be essential in Anabaena as the individual deletion mutants were non-viable. On the other hand, the proteins could be individually overexpressed in Anabaena with no effect on normal cell physiology. However, they contributed positively to enhance the tolerance to different DNA damage-inducing stresses, such as mitomycin C and UV- and γ-radiation. This indicated that the two proteins, at least when overexpressed, could function independently and mitigate the damage caused due to the formation of DNA adducts and single- and double-strand breaks in Anabaena. This is the first report on possible independent in vivo functioning of SbcC and SbcD homologs in any bacteria, and the first effort to functionally characterize the proteins in any cyanobacteria.     

Metatrancriptomic analysis from the Hepatopancreas of adult white leg shrimp (<Emphasis Type="Italic">Litopenaeus vannamei)</Emphasis>

The amoeba, Mayorella viridis contains several hundred symbiotic green algae in its cytoplasm. Transmission electron microscopy revealed strong resemblance between symbiotic algae from M. viridis the symbiotic Chlorella sp. in the perialgal vacuoles of Paramecium bursaria and other ciliates. Although it is thought that the M. viridis and symbiotic algae could be model organisms for studying endosymbiosis between protists and green algae, few cell biological observations of the endosymbiosis between M. viridis and their symbiotic algae have been published. In this study, we characterized the specificity of endosymbiotic relationships between green algae and their hosts. Initially, we established stable cultures of M. viridis in KCM medium by feeding with Chlorogonium capillatum. Microscopic analyses showed that chloroplasts of symbiotic algae in M. viridis occupy approximately half of the algal cells, whereas those in P. bursaria occupy entire algal cells. The symbiotic algae in P. bursaria contain several small spherical vacuoles. The labeling of actin filaments using Acti-stain? 488 Fluorescent Phalloidin revealed no relationship between host actin filaments and symbiotic algal localization, although the host mitochondria were localized around symbiotic algae. Symbiotic algae from M. viridis could infect algae-free P. bursaria but could not support P. bursaria growth without feeding, whereas the original symbiotic algae of P. bursaria supported its growth without feeding. These data indicated the specificity of endosymbiotic algae relationships in M. viridis and P. bursaria.     

Isolation of <Emphasis Type="Italic">Serratia marcescens</Emphasis> involved in chitin degradation in the bulb mite <Emphasis Type="Italic">Rhizoglyphus robini</Emphasis>

Cymbomonas tetramitiformis is a peculiar green alga that unites in one cell the abilities of photosynthesis and phagocytosis, which makes it a very useful model for the study of the evolution of plastid endosymbiosis. We have pondered over this issue and propose an evolutionary scenario of trophic strategies in eukaryotes, including primary and secondary plastid endosymbioses. C. tetramitiformis is a prototroph, just like the common ancestor of Archaeplastida was, and can synthesize most small organic molecules contrary to other eukaryotic phagotrophs, e.g. some metazoans, amoebozoans, and ciliates, which have not evolved tight endosymbiotic relationships. In order to establish a permanent photosynthetic endosymbiont they do not have to become prototrophs, but have to acquire the genes necessary for plastid retention via horizontal (including endosymbiotic) gene transfer. Such processes occurred successfully in the ancestors of eukaryotes with permanent secondary plastids and thus led to their great diversification. The preservation of phagocytosis in Cymbomonas (and some other prasinophytes as well) seems to result from nutrient deficiency in their oligotrophic habitats. This forces them to supplement their diet with phagocytized prey, in contrasts to the thecate amoeba Paulinella chromatophora, which also successfully transformed cyanobacteria into permanent organelles. Although Paulinella endosymbionts were acquired very recently in comparison to primary plastids, Paulinella has lost the ability to phagocytose, most probably due to the fact that it inhabits nutrient-rich environments, which renders the phagotrophy nonessential.     

Ecophysiological response of native and invasive <Emphasis Type="Italic">Spartina</Emphasis> species to extreme temperature events in Mediterranean marshes

The recent IPCC WG2 5th Assessment Report (IPCC 2014), notes an increase in the frequency and duration of extreme climatic events, especially for the Mediterranean region. Together with climate change, the invasion of natural communities by non-indigenous species (NIS) constitutes a serious threat to biodiversity. One of these NIS is the American Spartina patens, now present in Western European marshes. The present study aims to understand the biochemical and photochemical responses of S. patens compared with S. maritima under extreme temperature events. Under normal and extreme heat conditions, S. patens had a higher photosynthetic efficiency (α), compared with cold wave events, where the native S. maritima was far more efficient. This reduced photosynthetic efficiency was mostly due to a decrease in the connectivity between photosystem II (PSII) antennae. This was accompanied by severe damage to the oxygen-evolving complex of PSII. On the other hand, S. patens oxygen evolving complexes (OECs) seem to be temperature insensitive. The light absorption capacity was maintained due to a higher net rate of reaction centre (RC) closure as a counteractive measure of the reduced number of RC, especially in S. maritima. The loss of connectivity between PSII antennae and damage in OECs under heat stress leads to a severe reduction in the maximum yield for photochemistry enhanced by the low probability of each absorbed quanta to produce electronic work. However, while S. maritima presents high energy losses under heat stress, S. patens developed efficient quenching mechanisms under thermal stress, through auroxanthin. In S. patens, cold wave-treated individuals also displayed a very active line of enzymatic defences for reactive oxygen species scavenging. In fact, only cold treated individuals of this species presented higher activities of anti-oxidant enzymes, revealing some degree of adaptation to this new environment. In contrast, in S. maritima the exposure to extreme heat periods led, in most cases, to a decrease in the enzymatic defences, leaving the cell prone to oxidative damage. In summary, S. patens appears to have a higher fitness for the incoming climatic scenarios, being more tolerant to heat stress, while S. maritima will have its photobiological fitness decreased. This will impose a shift in the salt marsh biodiversity, favouring the non-indigenous S. patens expansion.     

Waterbird response indicates floodplain wetland restoration

Filamentous cyanobacteria disturb food collection in Daphnia by mechanical interference with the filtering apparatus by the long trichomes. The intensity of this interference depends on the water temperature and the Daphnia body size. However, Daphnia are capable of breaking down the filaments, therefore improving the palatability of the cyanobacteria. The main objective of this study was to test whether the shortening of cyanobacterial filaments and the ensuing clearance rate of Daphnia would increase at higher temperatures to a greater degree in small-bodied Daphnia species than in large-bodied one. Laboratory feeding experiments were conducted in order to measure variation in the length of Cylindrospermopsis raciborskii trichomes and to calculate clearance rate. The filament length and the cyanobacteria clearance rate by Daphnia were calculated following their exposure to grazing by large-bodied D. pulicaria and small-bodied D. longispina in 20, 24, and 28°C. Rising temperature did not affect the intensity of breakage of C. raciborskii trichomes by D. pulicaria and caused decrease in clearance rate of this species, whereas for D. longispina, the temperature increase enhanced both filament breakage and clearance rate. We suggest that these temperature-related changes may affect relative competitive performance of Daphnia species in the presence of cyanobacteria.     

Comparative study on mitogenomes of green tide algae

Since 2007, the annual green tide disaster in the Yellow Sea has brought serious economic losses to China. There is no research on the genetic similarities of four constituent species of green tide algae at the genomic level. We previously determined the mitochondrial genomes of Ulva prolifera, Ulva linza and Ulva flexuosa. In the present work, the mitochondrial genome of another green tide (Ulva compressa) was sequenced and analyzed. With the length of 62,311 bp, it contained 29 encoding genes, 26 tRNAs and 10 open reading frames. By comparing these four mitochondrial genomes, we found that U. compressa was quite different from the other three types of Ulva species. However, there were similarities between U. prolifera and U. linza in the number, distribution and homology of open reading frames, evolutionary and codon variation of tRNA, evolutionary relationship and selection pressure of coding genes. Repetitive sequence analysis of simple sequence repeats, tandem repeat and forward repeats further supposed that they have evolved from the same origin. In addition, we directly analyzed gene homologies and translocation of four green tide algae by Mauve alignment. There were gene order rearrangements among them. With fast-evolving genomes, these four green algal mitochondria have both conservatism and variation, thus opening another window for the understanding of origin and evolution of Ulva.     

<Emphasis Type="Italic">Sr33</Emphasis> and <Emphasis Type="Italic">Sr35</Emphasis> gene homolog identification in genomes of cereals related to <Emphasis Type="Italic">Aegilops tauschii</Emphasis> and <Emphasis Type="Italic">Triticum monococcum</Emphasis>

Using bioinformatics analysis, the homologs of genes Sr33 and Sr35 were identified in the genomes of Triticum aestivum, Hordeum vulgare, and Triticum urartu. It is known that these genes confer resistance to highly virulent wheat stem rust races (Ug99). To identify amino acid sites important for this resistance, the found homologs were compared with the Sr33 and Sr35 protein sequences. It was found that sequences S5DMA6 and E9P785 are the closest homologs of protein RGAle, a Sr33 gene product, and sequences M7YFA9 (CNL-C) and F2E9R2 are homologs of protein CNL9, a Sr35 gene product. It is assumed that the homologs of genes Sr33 and Sr35, which were obtained from the wild relatives of wheat and barley, can confer resistance to various forms of stem rust and can be used in the future breeding programs aimed at improvement of national wheat varieties.     

Morphological and molecular characterization of cyanobacteria from a Brazilian facultative wastewater stabilization pond and evaluation of microcystin production

The cyanobacterial population in the Cajati waste stabilization pond system (WSP) from São Paulo State, Brazil was assessed by cell isolation and direct microscope counting techniques. Ten strains, belonging to five genera (Synechococcus, Merismopedia, Leptolyngbya, Limnothrix, and Nostoc), were isolated and identified by morphological and molecular analyses. Morphological identification of the isolated strains was congruent with their phylogenetic analyses based on 16S rDNA gene sequences. Six cyanobacterial genera (Synechocystis, Aphanocapsa, Merismopedia, Lyngbya, Phormidium, and Pseudanabaena) were identified by direct microscope inspection. Both techniques were complementary, since, of the six genera identified by direct microscopic inspection, only Merismopedia was isolated, and the four other isolated genera were not detected by direct inspection. Direct microscope counting of preserved cells showed that cyanobacteria were the dominant members (>90%) of the phytoplankton community during both periods evaluated (summer and autumn). ELISA tests specific for hepatotoxic microcystins gave positive results for six strains (Synechococcus CENA108, Merismopedia CENA106, Leptolyngbya CENA103, Leptolyngbya CENA112, Limnothrix CENA109, and Limnothrix CENA110), and for wastewater samples collected from raw influent (3.70 μg microcystins/l) and treated effluent (3.74 μg microcystins/l) in summer. Our findings indicate that toxic cyanobacteria in WSP systems are of concern, since the treated effluent containing cyanotoxins will be discharged into rivers, irrigation channels, estuaries, or reservoirs, and can affect human and animal health.     

Evaluation of growth and phycobiliprotein composition of cyanobacteria isolates cultivated in different nitrogen sources

Phycobiliproteins, light-harvesting pigments found in cyanobacteria and in some eukaryotic algae, have numerous commercial applications in food, cosmetic, and pharmaceutical industries. Colorant production from cyanobacteria offers advantages over their production from higher plants, as cyanobacteria have fast growth rate and high photosynthetic efficiency and require less space. In this study, three cyanobacteria strains were studied for phycobiliprotein production and the influence of sodium nitrate, potassium nitrate and ammonium chloride on the growth and phycobiliprotein composition of the strains were evaluated. In the batch culture period of 12 days, Phormidium sp. and Pseudoscillatoria sp. were able to utilize all tested nitrogen sources; however, ammonium chloride was the best nitrogen source for both strains to achieve maximum growth rate μ?=?0.284?±?0.03 and μ?=?0.274?±?0.13 day^?1, chlorophyll a 16.2?±? 0.5 and 12.2?±? 0.2 mg L^?1, and phycobiliprotein contents 19.38?±?0.09 and 19.99?±?0.14% of dry weight, whereas, for Arthrospira platensis, the highest growth rate of μ?=?0.304?±?0.0 day^?1, chlorophyll a 19.1?±?0.5 mg L^?1, and phycobiliprotein content of 22.27?±?0.21% of dry weight were achieved with sodium nitrate. The phycocyanin from the lyophilized cyanobacterial biomass was extracted using calcium chloride and food grade purity (A₆₂₀/A₂₈₀ ratio >?0.7) was achieved. Furthermore, phycocyanin was purified using two-step chromatographic method and the analytical grade purity (A₆₂₀/A₂₈₀ ratio >?4) was attained. SDS-PAGE demonstrated the purity and presence of two bands corresponding to α- and β-subunits of the C-phycocyanin. The results showed that Phormidium sp. and Pseudoscillatoria sp. could be good candidates for phycocyanin production.     

Lipid metabolism and potentials of biofuel and high added-value oil production in red algae

Biomass production is currently explored in microalgae, macroalgae and land plants. Microalgal biofuel development has been performed mostly in green algae. In the Japanese tradition, macrophytic red algae such as Pyropia yezoensis and Gelidium crinale have been utilized as food and industrial materials. Researches on the utilization of unicellular red microalgae such as Cyanidioschyzon merolae and Porphyridium purpureum started only quite recently. Red algae have relatively large plastid genomes harboring more than 200 protein-coding genes that support the biosynthetic capacity of the plastid. Engineering the plastid genome is a unique potential of red microalgae. In addition, large-scale growth facilities of P. purpureum have been developed for industrial production of biofuels. C. merolae has been studied as a model alga for cell and molecular biological analyses with its completely determined genomes and transformation techniques. Its acidic and warm habitat makes it easy to grow this alga axenically in large scales. Its potential as a biofuel producer is recently documented under nitrogen-limited conditions. Metabolic pathways of the accumulation of starch and triacylglycerol and the enzymes involved therein are being elucidated. Engineering these regulatory mechanisms will open a possibility of exploiting the full capability of production of biofuel and high added-value oil. In the present review, we will describe the characteristics and potential of these algae as biotechnological seeds.     

Bio-optical characterization of selected cyanobacteria strains present in marine and freshwater ecosystems

The optical properties, i.e., absorption and scattering spectra of ten strains of cyanobacteria from the Baltic Sea and Pomeranian lakes (Aphanizomenon flos-aquae KAC 15, Microcystis aeruginosa CCNP 1101, Anabaena sp. CCNP 1406, Synechocystis salina CCNP 1104, Phormidium sp. CCNP 1317, Nodularia spumigena CCNP 1401, Synechococcus sp. CCNP 1108, Nostoc sp. CCNP 1411, Cyanobacterium sp. CCNP 1105, Pseudanabaena cf. galeata CCNP 1312) grown under low light conditions were investigated. Moreover, the chlorophylls, carotenoids, and phycobilin composition as well as the size structure of chosen cyanobacteria were measured. Studied species revealed high diversity both in optical properties with the absorption spectra similarity index ranging from 0.67 to 0.94 and the pigment composition. The chlorophyll-specific absorption coefficient at 440 nm a _ph *(440) varied between 0.017 and 0.065 m² mg^?1. The influence of the package effect was only observed in the case of large filamentous cyanobacteria like N. spumigena or Nostoc sp. Interestingly, the package effect factor Q _a *(675) for large-celled Anabaena sp. was 0.92. Besides chlorophyll a, only echinenone, β-carotene, and phycocyanin were present in all analyzed cyanobacteria strains. Zeaxanthin, which is widely used as a marker pigment for cyanobacteria, was absent in the toxic N. spumigena and Anabaena sp., which are the species that occur in the Baltic Sea most frequently causing summer cyanobacterial blooms. The investigation also showed that the sample preservation technique can introduce some major errors within the absorption band affected by the phycocyanin absorption.     

Experimental associations of cyanobacteria and actinomycetes

Associations of cyanobacteria with actinomycetes are not being investigated. The purpose of this study is to investigate the biological aspects of coexistence of the free-living Anabaena variabilis with actinomycetes isolated from apogeotropic roots of Strangeria eriopus and Cycas micholitzii; with the cyanobacterium Oscillatoria terebriformis (Ag.) Elenk. emend., which were isolated from the natural cyanobacterial mat taken from the Kamchatkan thermal spring; and with actinomycetes isolated from the accumulating culture of cyanobacterium. Positive tropism of actinomycete hyphae to cyanobacterial trichomes and that of the cyanobacterium to streptomycetes were observed. Stimulation of growth of O. terebriformis in the associated culture with the streptomycete was recorded. The increase of fixation of nitrogen by A. variabilis and of photosynthetic activity of O. terebriformis in the associated culture with the streptomycete was recorded.     

Heterologous expression of two <Emphasis Type="Italic">Physcomitrella patens</Emphasis> group 3 late embryogenesis abundant protein (LEA3) genes confers salinity tolerance in arabidopsis

Salinity stress is a major limiting factor in agriculture and adversely affecting the whole plant. As a halophyte, the moss Physcomitrella patens, has been suggested to be an ideal model plant to study salinity tolerance and adaption. Two abiotic stress-responsive Group 3 Late Embryogenesis Abundant protein genes had been identified in P. patens and named as PpLEA3-1 and PpLEA3-2, respectively. Functions of these two genes were analyzed by heterologous expressions in Arabidopsis, driven either by their native P. patens promoters or by the 35S CaMV constitutive promoter. Phenotype analysis revealed that pLEA3::LEA3, pLEA3::LEA3::GFP and 35S::LEA3::GFP transgenic lines had stronger salinity resistance than that in the wild type and empty-vector control. Further analysis showed that the contents of proline and soluble sugar were increased and the malondialdehyde (MDA) were repressed in these transgenic plants after exposure to salinity stress. Our observations indicate that these two Group 3 PpLEA genes played a role in the adaption to salinity stress.