Browsing by Author "Keshawanand Tripathi"

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An alkaline phosphatase/phosphodiesterase, PhoD, induced by salt stress and secreted out of the cells of Aphanothece halophytica, a halotolerant cyanobacterium
(2011) Hakuto Kageyama; Keshawanand Tripathi; Ashwani K. Rai; Suriyan Cha-Um; Rungaroon Waditee-Sirisattha; Teruhiro Takabe
Alkaline phosphatases (APases) are important enzymes in organophosphate utilization. Three prokaryotic APase gene families, PhoA, PhoX, and PhoD, are known; however, their functional characterization in cyanobacteria largely remains to be clarified. In this study, we cloned the phoD gene from a halotolerant cyanobacterium, Aphanothece halophytica (phoD Ap). The deduced protein, PhoD Ap, contains Tat consensus motifs and a peptidase cleavage site at the N terminus. The PhoD Ap enzyme was activated by Ca 2+ and exhibited APase and phosphodiesterase (APDase) activities. Subcellular localization experiments revealed the secretion and processing of PhoD Ap in a transformed cyanobacterium. Expression of the phoD Ap gene in A. halophytica cells was upregulated not only by phosphorus (P) starvation but also under salt stress conditions. Our results suggest that A. halophytica cells possess a PhoD that participates in the assimilation of P under salinity stress. © 2011, American Society for Microbiology.
Fungal Siderophore: Biosynthesis, Transport, Regulation, and Potential Applications
(Springer, 2020) Keshawanand Tripathi; Narendra Kumar; Meenakshi Singh; Ravi Kant Singh
Iron (Fe) is an essential nutrient for life and the fourth most abundant element in the earth. The availability of ferric iron (Fe III) is less in soil solution due to the low solubility of ferric hydroxides, oxides, and oxyhydroxides. Therefore, the Fe availability to microbes and plants is limited, albeit its abundance in the environment. Therefore, the availability of Fe to microbes and plants has evolved strategies based on acidification through proton extrusion and organic acid production, chelation, ligands like siderophore and phytosiderophore production, and enzymatic reduction involving reductase enzymes. This review attempts to explain the fungal siderophore, its biosynthesis, transport, and practical application. Thus, siderophore is an iron-binding molecule synthesized by fungi, bacteria, cyanobacteria, and plants. The common types of siderophore are hydroxamates, catecholates, carboxylates, but hydroxamate type is dominant in fungi. L-ornithine is a biosynthetic precursor of siderophore and synthesized through multimodular large enzymes complex nonribosomal peptide synthetase (NRPSs) dependent/independent. Siderophore-Fe chelators protein (FIT1, FIT2, and FIT3) helps in the retention of siderophore. Saccharomyces cerevisiae expresses two genetically separate systems (reductive and a non-reductive system) at the plasma membrane, which converts Fe III into Fe II by ferrous-specific metallo-reductases enzyme complex, FRE reductases. Regulation of the siderophore gene expression on the promoter region by Fur Box protein depends on the availability of Fe in the external medium. Biotechnologically, it is more important due to its wide range of applications that include medical, remediation of heavy metal, biocontrol of plant pathogens, and enzyme inhibitions. © Springer Nature Singapore Pte Ltd. 2020.
Interplay of hydrogen sulfide and plant metabolites under environmental stress
(Elsevier, 2023) Akhilesh Kumar Pandey; Subhomoi Borokotoky; Keshawanand Tripathi; Arti Gautam
Hydrogen sulfide (H2S) has emerged as a potent regulator of several physiological processes of the plant system, including providing tolerance to various abiotic stresses. Initially, H2S was known for its toxic properties, but its versatile biological functions came into the limelight when its endogenous production inside plant cells was discovered. Endogenous production of H2S in plants occurs in cellular components and plays a key role in antioxidant activities, the synthesis of osmoregulators, the production of cell signaling proteins, various gene expressions, crucial metabolical activities and hence the synthesis of plant metabolites. Plant metabolites are intermediates and end products of metabolical processes that are essential for the existence of plants. Plant metabolites are directly or indirectly involved in various physiological and biochemical processes in plants and aid in normal plant growth and development. H2S has been investigated for its involvement in triggering gene expression to synthesize plant metabolites. It also interacts with metabolites such as nitric oxide, hydrogen peroxide (H2O2), calcium ions (Ca2+), abscisic acid, jasmonic acid, ethylene, salicylic acid, melatonin, polyamines, proline, and methylglyoxal in plants. This article presents current knowledge about the biosynthesis of H2S and its role in maintaining physiological homeostasis in plants. That presentation is followed by a detailed description of the roles of plant metabolites in metabolic processes and basic life functions. This chapter summarizes the interactive roles of H2S and plant metabolites in regulating various physiological functions essential for plant survival. © 2024 Elsevier Inc. All rights reserved.
Low cellular P-quota and poor metabolic adaptations of the freshwater cyanobacterium Anabaena fertilissima Rao during Pi-limitation
(2013) Keshawanand Tripathi; Naveen K. Sharma; Vandna Rai; Ashwani K. Rai
Anabaena fertilissima is a filamentous freshwater N2-fixing cyanobacterium, isolated from a paddy field. Growth of the cyanobacterium was limited by the non-availability of inorganic phosphate (Pi) in the growth medium and was found to be directly related to the cellular P quota, which declined rapidly in Pi-deficient cells. To overcome Pi-deficiency, cells induced both cell-bound and cell-free alkaline phosphatase activities (APase). The activity of cell-bound APase was rapid and 5-6 times higher than that of the cell-free APase activity. Native gel electrophoresis revealed the presence of two APase activity bands for both the cell bound and cell-free APase (Mr ≈42 and 34 kDa). For Pi-deficient cells, APase activity was inversely related to cellular P-quota. In A. fertilissima phosphate uptake was facilitated by single high-affinity phosphate transporter (K s, 4.54 μM; V max, 4.84 μmol mg protein-1 min-1). Pi-deficiency severely reduced the photosynthetic rate, respiration rate and nitrate uptake, as well as the activities of nitrate reductase, nitrite reductase and nitrogenase enzymes. In photosynthesis, PSII activity was maximally inhibited, followed by PSI and whole chain activities. Transcript levels of five key glycolytic enzymes showed the poor adaptability of the cyanobacterium to switch its metabolic activity to PPi-dependent enzyme variants, which has rather constant cellular concentrations. © 2012 Springer Science+Business Media B.V.
Proteomic evaluation of the freshly isolated cyanobionts from Azolla microphylla exposed to salinity stress
(Springer Netherlands, 2019) Ravindra Kumar Yadav; Keshawanand Tripathi; Vagish Mishra; Pramod Wasudeo Ramteke; Pawan Kumar Singh; Gerard Abraham
The cyanobiont Anabaena azollae performs nitrogen fixation in the agronomically important Azolla-Anabaena system. However, the response of the cyanobiont to salinity has not been studied at the molecular level. In the present study Azolla microphylla plants were exposed to salinity (90 mM NaCl) for 3 days and the cyanobionts have been isolated. The proteome profile of the freshly isolated cyanobionts were investigated by Two dimensional gel electrophoresis (2DE) followed by MALDI-TOF-MS/MS analysis. Sixty eight protein spots showed significant changes in response to salinity treatment and out of those proteins, 18 protein spots were identified. Among them 12 proteins were up regulated whereas 6 proteins were down regulated. Up regulation of important proteins related to protein synthesis and cell signaling may be involved in the response of the cyanobiont to adapt to short term salinity exposure. The study might help in understanding the biological processes and stress proteins involved in salinity stress adaptation in the cyanobiont A. azollae. © 2018, Springer Nature B.V.
Salinity induced changes in the chloroplast proteome of the aquatic pteridophyte Azolla microphylla
(Springer Netherlands, 2018) Preeti Thagela; Ravindra Kumar Yadav; Keshawanand Tripathi; Pawan Kumar Singh; Altaf Ahmad; Anil Dahuja; Gerard Abraham
The growth of the nitrogen fixing aquatic pteridophyte Azolla microphylla is severely affected by salinity. Salinity exposure (0.5%) resulted in significant reduction in chlorophyll a and b content, altered chl a/b ratio and photosynthetic efficiency (Fv/Fm). Chloroplasts maintain photosynthesis but are highly sensitive to salinity stress. Chloroplast proteins extracted from A. microphylla was separated by two-dimensional electrophoresis (2DE) and approximately 200 proteins were observed on each gel. Forty two differentially expressed protein spots were detected and out of this 17 could be identified through MALDI-TOF-MS/MS analysis. Out of the 17 identified proteins, 15 were found to be down regulated and 2 proteins were up regulated. Most of the down regulated proteins were associated with Calvin cycle, ATP synthesis, oxygen evolution, photosystem I and ROS scavenging. The results show changes in proteome dynamics of the chloroplasts of A. microphylla and such changes may lead to reduction in growth and metabolism. The primary target of salinity in A. microphylla is photosynthesis and the changes in the proteome dynamics of the chloroplasts lead to reduced growth. © 2017, Springer Science+Business Media B.V.
Sample preparation method for tissue based proteomic analysis of Azolla microphylla
(Springer Netherlands, 2017) Preeti Thagela; Ravindra Kumar Yadav; Vagish Mishra; Keshawanand Tripathi; Altaf Ahmad; Anil Dahuja; Pawan Kumar Singh; Gerard Abraham
The nitrogen fixing aquatic pteridophyte Azolla is used as biofertilizer for rice paddy. It is also used as poultry and cattle feed due to high protein content. However, its mass cultivation and exploitation is constrained due to the abiotic stress conditions it is exposed to. The system is interesting due to the presence of symbiotic nitrogen fixing cyanobacteria and its interaction with the carbon fixing host. Therefore these interactions have to be studied at the molecular level using advanced techniques. Proteomics is a technique which can be employed to reveal the mechanism of cross talk between the host and its symbiont as well as its response to abiotc stress. The primary step that contributes to successful proteomic analysis is standardization of sound protocols for protein extraction and sufficient yield to initiate proteomic studies using 2-dimensional electrophoresis. However, reports are not available on the protein extraction procedures in Azolla. Therefore in the present study we attempted to optimize protein extraction protocol in the whole plant, roots and the chloroplast of Azolla microphylla using phenol extraction, TCA-acetone and phosphate buffer methods. Our studies showed the efficacy of phenol extraction method in terms of maximum yield and resolution of proteins in Azolla. © 2016, Springer Science+Business Media Dordrecht.