Kamala Gupta

Plant polyamines in abiotic stress responses

Significance of naturally occurring intracellular polyamines (PAs), such as spermine, spermidine, and putrescine, in relation to the mechanism and adaptation to combat abiotic stress has been well established in plants. Because of their polycationic nature at physiological pH, PAs bind strongly to negative charges in cellular components such as nucleic acids, proteins, and phospholipids. Accumulation of the three main PAs occurs under many types of abiotic stress, and modulation of their biosynthetic pathway confers tolerance to drought or salt stress. Maintaining crop yield under adverse environmental conditions is probably the major challenge faced by modern agriculture, where PAs can play important role. Over the last two decades, genetic, transcriptomic, proteomic, metabolomic, and phenomic approaches have unraveled many significant functions of different PAs in the regulation of plant abiotic stress tolerance. In recent years, much attention has also been devoted to the involvement of PAs in ameliorating different environmental stresses such as osmotic stress, drought, heat, chilling, high light intensity, heavy metals, mineral nutrient deficiency, pH variation, and UV irradiation. The present review discusses the various reports on the role of PAs in the abiotic stress of plants with a note on current research tendencies and future perspectives. Co-relating all these data into a signal network model will be an uphill task, and solving this will give a clearer picture of the intricate abiotic stress signalling network in the plant kingdom.

Polyamines as redox homeostasis regulators during salt stress in plants

The balance between accumulation of stress-induced polyamines and reactive oxygen species (ROS) is arguably a critical factor in plant tolerance to salt stress. Polyamines are compounds, which accumulate in plants under salt stress and help maintain cellular ROS homeostasis. In this review we first outline the role of polyamines in mediating salt stress responses through their modulation of redox homeostasis. The two proposed roles of polyamines in regulating ROS – as antioxidative molecules and source of ROS synthesis – are discussed and exemplified with recent studies. Second, the proposed function of polyamines as modulators of ion transport is discussed in the context of plant salt stress. Finally, we highlight the apparent connection between polyamine accumulation and programmed cell death induction during stress. Thus polyamines have a complex functional role in regulating cellular signaling and metabolism during stress. By focusing future efforts on how polyamine accumulation and turnover is regulated, research in this area may provide novel targets for developing stress tolerance.

Hydrogen Peroxide and Polyamines Act as Double Edged Swords in Plant Abiotic Stress Responses

The specific genetic changes through which plants adapt to the multitude of environmental stresses are possible because of the molecular regulations in the system. These intricate regulatory mechanisms once unveiled will surely raise interesting questions. Polyamines and hydrogen peroxide have been suggested to be important signaling molecules during biotic and abiotic stresses. Hydrogen peroxide plays a versatile role from orchestrating physiological processes to stress response. It helps to achieve acclimatization and tolerance to stress by coordinating intra-cellular and systemic signaling systems. Polyamines, on the other hand, are low molecular weight polycationic aliphatic amines, which have been implicated in various stress responses. It is quite interesting to note that both hydrogen peroxide and polyamines have a fine line of inter-relation between them since the catabolic pathways of the latter releases hydrogen peroxide. In this review we have tried to illustrate the roles and their multifaceted functions of these two important signaling molecules based on current literature. This review also highlights the fact that over accumulation of hydrogen peroxide and polyamines can be detrimental for plant cells leading to toxicity and pre-mature cell death.

Genome-wide analysis and evolutionary study of sucrose non-fermenting 1-related protein kinase 2 (SnRK2) gene family members in Arabidopsis and Oryza.

The over-expression of plant specific SnRK2 gene family members by hyperosmotic stress and some by abscisic acid is well established. In this report, we have analyzed the evolution of SnRK2 gene family in different plant lineages including green algae, moss, lycophyte, dicot and monocot. Our results provide some evidences to indicate that the natural selection pressure had considerable influence on cis-regulatory promoter region and coding region of SnRK2 members in Arabidopsis and Oryza independently through time. Observed degree of sequence/motif conservation amongst SnRK2 homolog in all the analyzed plant lineages strongly supported their inclusion as members of this family. The chromosomal distributions of duplicated SnRK2 members have also been analyzed in Arabidopsis and Oryza. Massively Parallel Signature Sequencing (MPSS) database derived expression data and the presence of abiotic stress related promoter elements within the 1 kb upstream promoter region of these SnRK2 family members further strengthen the observations of previous workers. Additionally, the phylogenetic relationships of SnRK2 have been studied in all plant lineages along with their respective exon-intron structural patterns. Our results indicate that the ancestral SnRK2 gene of land plants gradually evolved by duplication and diversification and modified itself through exon-intron loss events to survive under environmental stress conditions.

Isolation and characterization of heavy metal tolerant Gram-positive bacteria with bioremedial properties from municipal waste rich soil of Kestopur canal (Kolkata), West Bengal, India

The present study was conducted to determine the culturable bacterial profile from Kestopur canal (Kolkata, India) and analyze their heavy metal tolerance. In addition to daily sewage including solid and soluble wastes, a considerable load of toxic metals are released into this water body from industries, tanneries and agriculture, household as well as health sectors. Screening out microbes from such an environment was done keeping in mind their multifunctional application especially for bioremediation. Heavy metals are major environmental pollutants when present in high concentration in soil and show potential toxic effects on growth and development in plants and animals. Some edible herbs growing in the canal vicinity, and consumed by people, were found to harbour these heavy metals at sub-toxic levels. The bioconcentration factor of these plants being <1 indicates that they probably only absorb but not accumulate heavy metals. All the thirteen Grampositive bacteria isolated from these plants rhizosphere were found to tolerate high concentration of heavy metals like Co, Ni, Pb, Cr, Fe. Phylogenetic analysis of their 16S rDNA genes revealed that they belonged to one main taxonomic group — the Firmicutes. Seven of them were found to be novel with 92–95% sequence homology with known bacterial strains. Further microbiological analyses show that the alkaliphilic Bacillus weihenstephanensis strain IA1 and Exiguobacterium aestuarii strain CE1, with selective antibiotic sensitivity along with high Ni2+ and Cr6+ removal capabilities, respectively, can be prospective candidates for bioremediation.

Spermidine-mediated in vitro phosphorylation of transcriptional regulator OSBZ8 by SNF1-type serine/threonine protein kinase SAPK4 homolog in indica rice

Plants respond to abiotic stresses such as salinity, extreme temperature and drought by the activation of complex intracellular signaling cascades that regulate acclimatory biochemical and physiological changes. Protein kinases are major signal transduction factors that play a central role in mediating acclimation to environmental changes in eukaryotic organisms. It is well known that changes in abiotic conditions such as the concentration of ions, temperature and humidity lead to modulation of polyamine contents in plants. However, little is known about the relevant part these polyamines play in abiotic stress responses. Here, we address a specific role of spermidine during high salt stress by studying its interaction with OSPDK, a sucrose nonfermenting 1-related protein kinase2 (SnRK2)-type serine/threonine protein kinase SAPK4 homolog in indica rice. In this report, we demonstrate that spermidine mediates in vitro phosphorylation of OSBZ8, a bZIP class of ABRE-binding transcription factor, by OSPDK. Our results give a first-hand indication of the pivotal role played by polyamines in abiotic stress cell signaling in plants.

In silico characterization and evolutionary analyses of CCAAT binding proteins in the lycophyte plant Selaginella moellendorffii genome: A growing comparative genomics resource

NF-Y transcription factors encoded by HAP gene family, composed of three subunits (HAP2/NF-YA, HAP3/NF-YB and HAP5/NF-YC), are capable of transcriptional regulation of target genes with high specificity by binding to the CCAAT-containing promoter sequences. Here, we have characterized duplicated HAP genes in Selaginella moellendorffii and explored some features that might be involved in the regulation of gene expression and their function. Subsequently, the evolutionary relationships of LEC1-type of HAP3 genes have been studied starting from lycophytes to angiosperm to reveal the details of conservation and diversification of these genes during plant evolution. Computational analyses demonstrated the variation in length of cis-regulatory region of HAP3 duplicates in S. moellendorffii containing three thermodynamically stable and evolutionarily conserved RNA secondary structures. The homology modeling of NF-Y proteins, secondary structural details, DNA binding large positive patches, binding affinity of H2A-H2B interactive residues of NF-YC subunits on the duplicated NF-YB subunits, conserved domain analyses and protein structural alignments indicated that gene duplication process of HAP genes in S. moellendorffii, followed by structural diversification, provide specific hints about their functional specificity under various circumstances for the survival of this lycophytic plant. We have identified several conserved motifs in LEC1 proteins among all plant lineages during evolution.

The Attributes of RNA Interference in Relation to Plant Abiotic Stress Tolerance

Micro RNAs are small non coding RNA molecule that plays a vital role in post transcriptional gene regulation by either translational repression or by inducing mRNA cleavage. These small non coding RNAs have emerged as one of the master regulators of plant growth and development. Recent studies have revealed their role in abiotic stress responses. Expression level of several miRNA changes when exposed to drought, salinity, temperature variations and oxidative environment resulting in modulation of the expression of target genes that are associated with stress response. This review aims to focus on the regulatory role of plant micro RNAs during abiotic stress.

Conservation of AtTZF1, AtTZF2, and AtTZF3 homolog gene regulation by salt stress in evolutionarily distant plant species.

Arginine-rich tandem zinc-finger proteins (RR-TZF) participate in a wide range of plant developmental processes and adaptive responses to abiotic stress, such as cold, salt, and drought. This study investigates the conservation of the genes AtTZF1-5 at the level of their sequences and expression across plant species. The genomic sequences of the two RR-TZF genes TdTZF1-A and TdTZF1-B were isolated in durum wheat and assigned to chromosomes 3A and 3B, respectively. Sequence comparisons revealed that they encode proteins that are highly homologous to AtTZF1, AtTZF2, and AtTZF3. The expression profiles of these RR-TZF durum wheat and Arabidopsis proteins support a common function in the regulation of seed germination and responses to abiotic stress. In particular, analysis of plants with attenuated and overexpressed AtTZF3 indicate that AtTZF3 is a negative regulator of seed germination under conditions of salt stress. Finally, comparative sequence analyses establish that the RR-TZF genes are encoded by lower plants, including the bryophyte Physcomitrella patens and the alga Chlamydomonas reinhardtii. The regulation of the Physcomitrella AtTZF1-2-3-like genes by salt stress strongly suggests that a subgroup of the RR-TZF proteins has a function that has been conserved throughout evolution.

Polyamines: Osmoprotectants in Plant Abiotic Stress Adaptation

Environmental stress is one of the major threats affecting the living world. The most crucial function of plant is to induce different regulatory self-defence pathways in response to stress. Abiotic stresses such as drought, high temperature and salinity cause rapid depletion of cellular water leading to loss of crops and agricultural productivity worldwide. On exposure to these prevalent stresses, plant accumulates several polyhydroxylic compounds and zwitterionic alkylamines commonly known as osmolytes or compatible solutes. These are low molecular weight water soluble compounds providing stress tolerance when accumulated without hindering cellular mechanisms. Genes involved in the biosynthetic pathways of different osmolytes have been identified from various sources. Genetic engineering utilising these endogenous genes has resulted in development of transgenic varieties with better adaptability towards stress. Polyamines are ubiquitous biogenic amines that have been implicated in diverse cellular functions. The protective role of plant polyamines as osmolytes is still controversial and needs further investigation. However, there are some reports that suggest functional similarities between polyamines and other osmolytes commonly found in plant defence mechanism. Functions include protection of macromolecules, cellular pH maintenance, ROS scavenging, stabilisation of native protein structure, etc. Apart from these direct functions, exogenous application of polyamines results in the elevation of endogenous level of different osmolytes. Thus, polyamines play an indirect role in plant abiotic stress tolerance by participating in osmolyte synthesis in response to stress. In this review, we have dissected the role of polyamines as osmoprotectants.