Comparative proteomics unveils cross species variations in Anabaena under salt stress

Exploring the membrane proteome of the diazotropic cyanobacterium Anabaena PCC7120 through gel-based proteomics and in silico approaches

This paper focuses on the gel-based membrane proteomics from diazotrophic cyanobacterium Anabaena PCC7120 by modifying the protocol of Hall et al. [1]. The bioinformatic analysis revealed that 59 (29 integral, 30 peripheral) of the 67 proteins identified were membrane proteins. Of the 29 integral proteins, except Alr0834, the remaining 28 contained 1-12 transmembrane helices. Sixteen integral proteins harboring signal peptides (Sec/TAT/LipoP) suggest that protein targeting in Anabaena involves both sec-dependent and sec-independent pathways. While majority of photosynthesis and respiration proteins (21 of 24) were confined to broad pH gradient the hypothetical and unknown (12 of 13), and cell envelope proteins (3 of 3) preferred the narrow pH range. Of the 5 transporters and binding proteins, Na(+)/H(+)-exchanging protein and Alr2372 were present in broad, pstS1 and cmpD in narrow and cmpA was common to both pH ranges. The distribution of proteins across pH gradient, thus clearly indicates the functional and structural diversity in membrane proteome of Anabaena. It requires mention that protochlorophyllide oxido-reductase, Na(+)/H(+)-exchanging protein, All1355, Alr2055, Alr3514, Alr2903 and Alr2751 were new entries to the 2DE membrane protein profile of Anabaena. This study demonstrates suitability of the modified protocol for the study of membrane protein from filamentous cyanobacteria.

SIGNIFICANCE

Anabaena sp. PCC7120 is used as a model organism due to its agriculture significance as biofertilizer, close resemblance with higher plant chloroplast and availability of full genome sequence. Although cytosolic proteome has been explored a lot membrane proteins are still understudied as they are notoriously difficult to display using 2-D technology. Identification and characterization of these proteins is therefore required to elucidate and understand cellular mechanisms. The purpose of this study was to develop a protocol suitable for membrane protein extraction from Anabaena. Additionally, by homology comparison or domain assignment a possible function could be ascribed to novel uncharacterized proteins which will serve as a useful reference for further detailed studies of membrane system in filamentous cyanobacteria. Resolution of membrane proteins ranging from least (single transmembrane helix) to highly hydrophobic (several transmembrane helices) one on 2D gels recommends the gel based approach for identification of membrane proteomics from filamentous cyanobacteria. This article is part of a Special Issue entitled: Proteomics in India.

Comparative proteomics of oxidative stress response in three cyanobacterial strains native to Indian paddy fields

Three strains of photoautotrophic, heterocystous, nitrogen-fixing cyanobacterium Anabaena, native to Indian paddy fields, were examined for their tolerance and proteomic response to the frequently used weedicide paraquat (methyl viologen). Anabaena 7120 (LD50 dose: 2μM for 6h) and Anabaena L-31 (LD50 dose: 2μM for 5h) showed distinctly better tolerance than Anabaena doliolum (LD50 dose: 2μM for 3h), to methyl viologen induced oxidative stress. The proteomic response, at respective LD50 dose, was mapped by 2D gel protein electrophoresis followed by protein identification by MALDI-ToF mass spectrometry. About 92 and 41 oxidative stress-responsive proteins were identified from Anabaena L-31 and A. doliolum, respectively, and compared with methyl viologen responsive proteins reported from Anabaena 7120 earlier. Upregulation of proteins involved in oxidative stress alleviation and protein homeostasis and downregulation of photosynthesis and carbon metabolism related enzymes appeared to underlie the oxidative stress response in all three Anabaena strains. Reduced photosynthesis and cellular reserves of molecular energy [ATP+NAD(P)H] seemed to overwhelm the cellular machinery to combat oxidative stress and protein denaturation, in preference to other adaptations, while the strain specific differences observed in proteome response appeared to determine the methyl viologen tolerance of individual cyanobacterial strains. This article is part of a Special Issue entitled: Proteomics in India.

UV-B stress induced metabolic rearrangements explored with comparative proteomics in three Anabaena species

Comparative proteomics together with physiological variables revealed different responses among three species of diazotrophic cyanobacterium Anabaena exposed to UV-B stress at the same time points. Perceptible decline in PSII activity, ATP pool, nitrogenase activity and respiration rate was observed for all the three species; this being maximum in Anabaena doliolum, followed by Anabaena sp. PCC 7120 and minimum in Anabaena L31. Statistical analysis of the protein abundance divided majority of them as early accumulated in A. L31, late accumulated in A. sp. PCC 7120 and downregulated in A. doliolum. Tolerance of A. L31 may be ascribed to post-translational modification reflected through the highest number of protein isoforms in its proteome followed by A. PCC 7120 and A. doliolum. Furthermore, increase in abundance of cyanophycinase, glutamine synthetase and succinate semialdehyde dehydrogenase in A. L31 suggests operation of an alternate pathway for assimilation of nitrogen and carbon under UV-B stress. An early accumulation of four proteins viz., glutamate ammonia ligase (Alr2328), transketolase (Alr3344), inorganic pyrophosphatase (All3570), and trigger protein (Alr3681) involved respectively in amino acid metabolism, energy metabolism, biosynthesis of cofactor and trigger protein and chaperone like activity across three species, suggests them to be marker of UV-B stress in Anabaena spp. This article is part of a Special Issue entitled: Proteomics in India.

Birth of plant proteomics in India: a new horizon

In the post-genomic era, proteomics is acknowledged as the next frontier for biological research. Although India has a long and distinguished tradition in protein research, the initiation of proteomics studies was a new horizon. Protein research witnessed enormous progress in protein separation, high-resolution refinements, biochemical identification of the proteins, protein-protein interaction, and structure-function analysis. Plant proteomics research, in India, began its journey on investigation of the proteome profiling, complexity analysis, protein trafficking, and biochemical modeling. The research article by Bhushan et al. in 2006 marked the birth of the plant proteomics research in India. Since then plant proteomics studies expanded progressively and are now being carried out in various institutions spread across the country. The compilation presented here seeks to trace the history of development in the area during the past decade based on publications till date. In this review, we emphasize on outcomes of the field providing prospects on proteomic pathway analyses. Finally, we discuss the connotation of strategies and the potential that would provide the framework of plant proteome research.

BIOLOGICAL SIGNIFICANCE

The past decades have seen rapidly growing number of sequenced plant genomes and associated genomic resources. To keep pace with this increasing body of data, India is in the provisional phase of proteomics research to develop a comparative hub for plant proteomes and protein families, but it requires a strong impetus from intellectuals, entrepreneurs, and government agencies. Here, we aim to provide an overview of past, present and future of Indian plant proteomics, which would serve as an evaluation platform for those seeking to incorporate proteomics into their research programs. This article is part of a Special Issue entitled: Proteomics in India.

Salt acclimation of cyanobacteria and their application in biotechnology

The long evolutionary history and photo-autotrophic lifestyle of cyanobacteria has allowed them to colonize almost all photic habitats on Earth, including environments with high or fluctuating salinity. Their basal salt acclimation strategy includes two principal reactions, the active export of ions and the accumulation of compatible solutes. Cyanobacterial salt acclimation has been characterized in much detail using selected model cyanobacteria, but their salt sensing and regulatory mechanisms are less well understood. Here, we briefly review recent advances in the identification of salt acclimation processes and the essential genes/proteins involved in acclimation to high salt. This knowledge is of increasing importance because the necessary mass cultivation of cyanobacteria for future use in biotechnology will be performed in sea water. In addition, cyanobacterial salt resistance genes also can be applied to improve the salt tolerance of salt sensitive organisms, such as crop plants.

The long goodbye: the rise and fall of flavodoxin during plant evolution

Ferredoxins are electron shuttles harbouring iron-sulfur clusters that connect multiple oxido-reductive pathways in organisms displaying different lifestyles. Some prokaryotes and algae express an isofunctional electron carrier, flavodoxin, which contains flavin mononucleotide as cofactor. Both proteins evolved in the anaerobic environment preceding the appearance of oxygenic photosynthesis. The advent of an oxygen-rich atmosphere proved detrimental to ferredoxin owing to iron limitation and oxidative damage to the iron-sulfur cluster, and many microorganisms induced flavodoxin expression to replace ferredoxin under stress conditions. Paradoxically, ferredoxin was maintained throughout the tree of life, whereas flavodoxin is absent from plants and animals. Of note is that flavodoxin expression in transgenic plants results in increased tolerance to multiple stresses and iron deficit, through mechanisms similar to those operating in microorganisms. Then, the question remains open as to why a trait that still confers plants such obvious adaptive benefits was not retained. We compare herein the properties of ferredoxin and flavodoxin, and their contrasting modes of expression in response to different environmental stimuli. Phylogenetic analyses suggest that the flavodoxin gene was already absent in the algal lineages immediately preceding land plants. Geographical distribution of phototrophs shows a bias against flavodoxin-containing organisms in iron-rich coastal/freshwater habitats. Based on these observations, we propose that plants evolved from freshwater macroalgae that already lacked flavodoxin because they thrived in an iron-rich habitat with no need to back up ferredoxin functions and therefore no selective pressure to keep the flavodoxin gene. Conversely, ferredoxin retention in the plant lineage is probably related to its higher efficiency as an electron carrier, compared with flavodoxin. Several lines of evidence supporting these contentions are presented and discussed.

Positive correlation between PSI response and oxidative pentose phosphate pathway activity during salt stress in an intertidal macroalga

Studies have demonstrated that photosynthetic limitations and starch degradation are responses to stress; however, the relationship between the two is seldom described in detail. In this article, the effects of salt stress on photosynthesis, the levels of NADPH and total RNA, the starch content and the activities of glucose-6-phosphate dehydrogenase (G6PDH) and ribulose-5-phosphate kinase (RPK) were evaluated. In thalli that underwent salt treatments, the cyclic electron flow through PSI showed greater stress tolerance than the flow through PSII. Even though the linear electron flow was suppressed by DCMU, the cyclic electron flow still operated. The electron transport rate I (ETRI) increased as the salinity increased when the thalli recovered in seawater containing DCMU. These results suggested that PSI receives electrons from a source other than PSII. Furthermore, the starch content and RPK activity decreased, while the content of NADPH and total RNA, and the activity of G6PDH increased under salt stress. Soluble sugar from starch degradation may enter the oxidative pentose phosphate pathway (OPPP) to produce NADPH and ribose 5-phosphate. Data analysis suggests that NADPH provides electrons for PSI in Ulva prolifera during salt stress, the OPPP participates in the stress response and total RNA is synthesized in excess to assist recovery.