Salinity Responsive Genes Research Articles

Arabidopsis AGB1 participates in salinity response through bZIP17-mediated unfolded protein response

BackgroundPlant heterotrimeric G proteins respond to various environmental stresses, including high salinity. It is known that Gβ subunit AGB1 functions in maintaining local and systemic Na+/K+ homeostasis to accommodate ionic toxicity under salt stress. However, whether AGB1 contributes to regulating gene expression for seedling’s survival under high salinity remains unclear.ResultsWe showed that AGB1-Venus localized to nuclei when facing excessive salt, and the induction of a set of bZIP17-dependent salt stress-responsive genes was reduced in the agb1 mutant. We confirmed both genetic and physical interactions of AGB1 and bZIP17 in plant salinity response by comparing salt responses in the single and double mutants of agb1 and bzip17 and by BiFC assay, respectively. In addition, we show that AGB1 depletion decreases nuclei-localization of transgenic mRFP-bZIP17 under salt stress, as shown in s1p s2p double mutant in the Agrobacteria-mediated transient mRFP-bZIP17 expression in young seedlings.ConclusionsOur results indicate that AGB1 functions in S1P and/or S2P-mediated proteolytic processing of bZIP17 under salt stress to regulate the induction of salinity-responsive gene expression.

CONSTANS interacts with and antagonizes ABF transcription factors during salt stress under long-day conditions.

CONSTANS (CO) is a critical regulator of flowering that combines photoperiodic and circadian signals in Arabidopsis (Arabidopsis thaliana). CO is expressed in multiple tissues, including seedling roots and young leaves. However, the roles and underlying mechanisms of CO in modulating physiological processes outside of flowering remain obscure. Here, we show that the expression of CO responds to salinity treatment. CO negatively mediated salinity tolerance under long-day (LD) conditions. Seedlings from co-mutants were more tolerant to salinity stress, whereas overexpression of CO resulted in plants with reduced tolerance to salinity stress. Further genetic analyses revealed the negative involvement of GIGANTEA (GI) in salinity tolerance requires a functional CO. Mechanistic analysis demonstrated that CO physically interacts with 4 critical basic leucine zipper (bZIP) transcription factors; ABSCISIC ACID-RESPONSIVE ELEMENT BINDING FACTOR1 (ABF1), ABF2, ABF3, and ABF4. Disrupting these ABFs made plants hypersensitive to salinity stress, demonstrating that ABFs enhance salinity tolerance. Moreover, ABF mutations largely rescued the salinity-tolerant phenotype of co-mutants. CO suppresses the expression of several salinity-responsive genes and influences the transcriptional regulation function of ABF3. Collectively, our results show that the LD-induced CO works antagonistically with ABFs to modulate salinity responses, thus revealing how CO negatively regulates plant adaptation to salinity stress.

Nitric oxide, calmodulin and calcium protein kinase interactions in the response of Brassica napus to salinity stress.

Involvement of nitric oxide (NO) in plant metabolism and its connection with phytohormones has not been fully described, thus information about the role of this molecule in signalling pathways remains fragmented. In this study, the effects of NO on calmodulin (CAM), calcium protein kinase (CPK), content of phytohormones and secondary metabolites in canola plants under salinity stress were investigated. We applied 100 μM sodium nitroprusside as an NO source to canola plants grown under saline (100 mM NaCl) and non-saline conditions at the vegetative stage. Plant growth was negatively affected by salinity, but exogenous NO treatment improved growth. NO caused a significant increase in activity of CAT, SOD and POX through their enhanced gene expression in stressed canola. Salinity-responsive genes, namely CAM and CPK, were induced by NO in plants grown under salinity. NO application enhanced phenolic compounds, such as gallic acid and coumaric acid and flavonoid compound,s catechin, diadzein and kaempferol, in plants subjected to salinity. NO treatment enhanced abscisic acid and brassinosteroids but decreased auxin and gibberellin in stressed canola plants. The impacts of NO in improving stress tolerance in canola required CAM and CPK. Also, NO signalling re-established the phytohormone balance and resulted in enhanced tolerance to salt stress. Furthermore, NO improved salinity tolerance in canola by increasing enzymatic and non-enzymatic antioxidant content.

Applied Selenium as a Powerful Antioxidant to Mitigate the Harmful Effects of Salinity Stress in Snap Bean Seedlings

Selenium (Se) plays several significant roles in regulating growth, development and plant responses to various abiotic stresses. However, its influence on sulfate transporters (SULTRS) and achieving the harmony with other salt-tolerance features is still limited in the previous literatures. This study elucidated the effect of Se supplementation (5, 10 and 20 µM) on salt-stressed (50 mM NaCl) snap bean seedlings. Generally, the results indicated that Se had dual effects on the salt stressed seedlings according to its concentration. At a low level (5 µM), plants demonstrated a significant improvement in shoot (13.8%) and root (22.8%) fresh weight, chlorophyll a (7.4%), chlorophyll b (14.7%), carotenoids (23.2%), leaf relative water content (RWC; 8.5%), proline (17.2%), total soluble sugars (34.3%), free amino acids (FAA; 18.4%), K (36.7%), Ca (33.4%), K/Na ratio (77.9%), superoxide dismutase (SOD; 18%), ascorbate peroxidase (APX;12.8%) and guaiacol peroxidase (G-POX; 27.1%) compared to the untreated plants. Meanwhile, most of these responses as well as sulfur (S), Se and catalase (CAT) were obviously decreased in parallel with increasing the applied Se up to 20 µM. The molecular study revealed that three membrane sulfate transporters (SULTR1, SULTR2 and SULTR 3) in the root and leaves and salinity responsive genes (SOS1, NHX1 and Osmotin) in leaves displayed different expression patterns under various Se treatments. Conclusively, Se at low doses can be beneficial in mitigating salinity-mediated damage and achieving the functioning homeostasis to tolerance features.

Expression study of stress-related genes in salinity-treated transgenic Arabidopsis harboring soybean Response Regulator 34

Owing to their sessile nature, plants are easily affected by various extenal factors. Among those, drought and salinity are considered as the most common stresses, which often pose a threat to plant growth and development. Major effects of the drought and salinity are interconnected and drive similar series of molecular changes in plants. These alterations in response to the stress are under the regulation of various signaling pathways, including the engangement of evolutionarily conserved two-component systems (TCSs). Three components with distinct functions can be found in a functional TCS, which are histidine kinases (HKs), histidine-containing phosphotransfer proteins (HPts), and response regulator proteins (RRs). Previous research revealed that the soybean (Glycine max) GmRR34 acts as an important regulatory protein in plants under drought stress conditions. In this project, the investigation on the role of GmRR34 in osmotic stress responses was extended to salinity by examining the expression of a subset of salinity-responsive genes using RT-qPCR method. Our analyses showed that the transgenic Arabidopsis plants ectopically expressing GmRR34 displayed enhanced expression of several important stress-related genes, including Catalase 1 (CAT1), Stromal ascorbate peroxidase 1 (sAPX1), Copper/zinc superoxide dismutase 1 (CSD1), Sodium/hydrogen exchanger 1 (NHX1) and Salt overly sensitive 2 (SOS2). These results indicate that GmRR34-transgenic plants might be more salt-tolerant thanks to stronger activities of antioxidant enzymes and better capacity in maintaining cytosolic ion homeostasis. Therefore, it is highlighted the necessity to perform further studies to fully characterize the GmRR34 biological functions as well as explore its application potential in enhancing the salt tolerance of crop plants.

Metabolomic and transcriptomic analysis of Lycium chinese and L. ruthenicum under salinity stress

BackgroundHigh soil salinity often adversely affects plant physiology and agricultural productivity of almost all crops worldwide, such as the crude drug known as wolfberry. However, the mechanism of this action in wolfberry is not fully understood yet.ResultsHere in this study, we studied different mechanisms potentially in Chinese wolfberry (Lycium chinese, LC) and black wolfberry (L. ruthenicum, LR) under salinity stress, by analyzing their transcriptome, metabolome, and hormone changes. The hormone detection analysis revealed that the ABA content was significantly lower in LR than LC under normal condition, and increased sharply under salinity stress in LR but not in LC. The transcriptome analysis showed that the salinity-responsive genes in wolfberry were mainly enriched in MAPK signaling, amino sugar and nucleotide sugar metabolism, carbon metabolism, and plant hormone signal transduction pathways in LC, while mainly related to carbon metabolism and protein processing in endoplasmic reticulum in LR. Metabolome results indicated that LR harbored higher flavone and flavonoid contents than LC under normal condition. However, the flavone and flavonoid contents were hardly changed in LR, but increased substantially in LC when exposed to salinity stress.ConclusionsOur results adds ABA and flavone to mechanism understanding of salinity tolerance in wolfberry. In addition, flavone plays a positive role in resistance to salinity stress in wolfberry.

Comparative analysis of machine learning based classification for abiotic stress proteins

For thousands of years, cereals which include rice, wheat, maize, sorghum and millets etc. have been playing major role in human civilization. These are the principal components of human diet and important staples for daily survival of billions of people globally. The cereal crops belong to poaceae family and rich in vitamins, minerals and fiber. They are reported to reduce the coronary heart disease and other serious diseases. These crops are adversely affected by biotic and abiotic stresses like cold, drought, heat and salinity. With the advent of modern NGS technologies, the plethora of molecular data leads to infer many unexplored facts of the cereal crops using in-silico approach. In the present work, computational techniques were applied to study thoroughly the classification of abiotic stresses (cold, drought, heat and salinity) responsive genes in cereals. The datasets of four stress responsive genes in poaceae family was retrieved from public domain. The machine learning based methodologies namely, Random forest, Support Vector Machines and Deep Learning-Long Short-Term Memory (DL-LSTM) were applied. A comparative analysis was carried out for classification of the retrieved data with k-fold cross validation applying the machine learning techniques at different parameters. It was observed that for all the four sets of data, accuracy was maximum, i.e. 95.11%, 76.88%, 94.31% and 82.04% for cold, drought, heat and salinity, respectively using DL-LSTM. Comparison of the methodologies obviates the outperformance of deep leaning. Such approach of computational studies will help researchers to study the complex biological problems of gene classification more efficiently.

Transcriptome analysis reveals key genes in response to salinity stress during seed germination in Setaria italica

Salinity stress severely affects agricultural production. Seed germination is the most critical phase of plant life and is regulated by genetic and environmental factors. Setaria italica is an excellent model system for investigating the response to abiotic stresses. However, the key genes in response to salinity stress during seed germination in S. italica are largely unknown. Here, the transcriptional response of imbibed and radicle-protruded seeds to salinity stress revealed 4090 salinity responsive genes (SRGs) from the salt-tolerant cultivar Chigu 10 (CG) and salt-sensitive cultivar Fenghong 3 (FH) by RNA sequencing. Enrichment and expression pattern analysis indicated that the CG and FH cultivars exhibited specific similarities and preferences in the salinity stress response. Heatmap analysis suggested that S. italica seeds germinated under salinity stress required enhanced hormone regulation, more active primary metabolism and energy production, more cell wall modifications, and higher anticipation of autotrophic growth. Furthermore, functional validation experiments demonstrated that the SiDRM2 and SiKOR1 of SRGs significantly influenced seed germination under salinity stress. Collectively, our findings not only provide new insights into the regulatory mechanisms of seed germination under salinity stress, but also reveal promising gene resources to genetically improve the salt-tolerance capacity of S. italica and other crops.

A reference-grade genome identifies salt-tolerance genes from the salt-secreting mangrove species Avicennia marina

Water scarcity and salinity are major challenges facing agriculture today, which can be addressed by engineering plants to grow in the boundless seawater. Understanding the mangrove plants at the molecular level will be necessary for developing such highly salt-tolerant agricultural crops. With this objective, we sequenced the genome of a salt-secreting and extraordinarily salt-tolerant mangrove species, Avicennia marina, that grows optimally in 75% seawater and tolerates >250% seawater. Our reference-grade ~457 Mb genome contains 31 scaffolds corresponding to its chromosomes. We identified 31,477 protein-coding genes and a salinome consisting of 3246 salinity-responsive genes and homologs of 614 experimentally validated salinity tolerance genes. The salinome provides a strong foundation to understand the molecular mechanisms of salinity tolerance in plants and breeding crops suitable for seawater farming.

Physiological and molecular responses for long term salinity stress in common fig (Ficus carica L.).

The online version contains supplementary material available at (10.1007/s12298-020-00921-z).

Maize transcription factor ZmEREB20 enhanced salt tolerance in transgenic Arabidopsis

Soil salinity severely limits agricultural crop production worldwide. As one of the biggest plant specific transcription factor families, AP2/ERF members have been extensively studied to regulate plant growth, development and stress responses. However, the role of AP2/ERF family in maize salt tolerance remains largely unknown. In this study, we identified a maize AP2-ERF family member ZmEREB20 as a positive salinity responsive gene. Overexpression of ZmEREB20in Arabidopsis enhanced ABA sensitivity and resulted in delayed seed germination under salt stress through regulating ABA and GA related genes. ZmEREB20 overexpression lines also showed higher survival rates with elevated ROS scavenging toward high salinity. Furthermore, root hair growth inhibition by salt stress was markedly rescued in ZmEREB20 overexpression lines. Auxin transport inhibitor TIBA drastically enhanced root hair growth in ZmEREB20 overexpression Arabidopsis under salt stress, together with the increased expression of auxin-related genes, ion transporter genes and root hair growth genes by RNA-seq analysis. ZmEREB20 positively regulated salt tolerance through the molecular mechanism associated with hormone signaling, ROS scavenging and root hair plasticity, proving the potential target for crop breeding to improve salt resistance.

Salt tolerance involved candidate genes in rice: an integrative meta-analysis approach

BackgroundSalinity, as one of the main abiotic stresses, critically threatens growth and fertility of main food crops including rice in the world. To get insight into the molecular mechanisms by which tolerant genotypes responds to the salinity stress, we propose an integrative meta-analysis approach to find the key genes involved in salinity tolerance. Herein, a genome-wide meta-analysis, using microarray and RNA-seq data was conducted which resulted in the identification of differentially expressed genes (DEGs) under salinity stress at tolerant rice genotypes. DEGs were then confirmed by meta-QTL analysis and literature review.ResultsA total of 3449 DEGs were detected in 46 meta-QTL positions, among which 1286, 86, 1729 and 348 DEGs were observed in root, shoot, seedling, and leaves tissues, respectively. Moreover, functional annotation of DEGs located in the meta-QTLs suggested some involved biological processes (e.g., ion transport, regulation of transcription, cell wall organization and modification as well as response to stress) and molecular function terms (e.g., transporter activity, transcription factor activity and oxidoreductase activity). Remarkably, 23 potential candidate genes were detected in Saltol and hotspot-regions overlying original QTLs for both yield components and ion homeostasis traits; among which, there were many unreported salinity-responsive genes. Some promising candidate genes were detected such as pectinesterase, peroxidase, transcription regulator, high-affinity potassium transporter, cell wall organization, protein serine/threonine phosphatase, and CBS domain cotaining protein.ConclusionsThe obtained results indicated that, the salt tolerant genotypes use qualified mechanisms particularly in sensing and signalling of the salt stress, regulation of transcription, ionic homeostasis, and Reactive Oxygen Species (ROS) scavenging in response to the salt stress.

Integrative analyses of transcriptomics and metabolomics upon seed germination of foxtail millet in response to salinity

Salinity stress has become an expanding threat to food security worldwide. Revealing the mechanisms of salinity tolerance in plants has immense significance. Foxtail millet (Setaria italica L.) has been regarded as a model crop for exploring mechanisms under stress, considering its extreme adaptation abilities to adverse ecologies. In present study, two foxtail millet cultivars of Yugu2 and An04 with contrasting salt tolerance properties were investigated through integrative analyses of transcriptomics and metabolomics. In the transcriptomics results, 8887 and 12,249 DEGs were identified in Yugu2 and An04 in response to salinity, respectively, and 3149 of which were overlapped between two varieties. These salinity-responsive genes indicated that ion transport, redox homeostasis, phytohormone metabolism, signaling and secondary metabolism were enriched in Yugu2 by GO and KEGG analyses. The integrative omics analysis implied that phenylpropanoid, flavonoid and lignin biosynthesis pathways, and lysophospholipids were vital in determining the foxtail millet salinity tolerance. Importantly, the tolerance of Yugu2 attributed to higher efficiencies of ion channel and antioxidant system. All these provide a comprehensive regulatory network of foxtail millet to cope with salinity, and shed some lights on salt tolerance which is relevant for other cereal crops.

Identification of salinity responsive genes in lavender through cDNA-AFLP

Currently, a global demand exists forlavender as a significant medicinal plant and source of essential oils. Freshwater and arable lands are two major factors that inhibit extensive farming of medicinal plants in Iran. Saline water from seas and salty soil may be new resources for agricultural use, especially for medicinal plants. We sought to extend our knowledge of the Lavandula angustifolia genome and molecular basis of its salinity tolerance by using cDNA amplified fragment length polymorphism (cDNA-AFLP) to investigate the changes in plant transcriptomes in response to NaCl. All identified transcript derived fragments (TDF) were assigned as novel L. angustifolia genes related to signal transduction, regulation of gene expression, alternative splicing, autophagy, and secondary metabolite biosynthesis. qRT-PCR analysis of the TDFs in response to different concentrations of NaCl revealed various levels of mRNA of the identified genes in this plant. Our findings provided primary insights into the molecular response of L. angustifolia to salinity.

Shedding light on response of Triticum aestivum cv. Kharchia Local roots to long-term salinity stress through transcriptome profiling

Among the various abiotic stresses, salinity is one of the major limitations for production and productivity of wheat. Kharchia Local is the most salt-tolerant wheat cultivar developed from farmers’ selection on salt affected areas of India. Here, to investigate the molecular response of Kharchia Local under salinity stress, transcriptome sequencing of root tissue samples at the anthesis stage was performed. Illumina sequencing generated a total of 82.84 million clean reads and were assembled into 1,18,200 unigenes. A set of 10,805 unigenes were differentially expressed in response to salinity stress. Around 8232 unigene-derived SSRs were mined from these DEGs that can be used as functional molecular markers. Expression pattern of salinity stress-responsive unigenes was validated using real time PCR and results were found to be consistent with that of transcriptome profiling. Functional annotation of DEGs against GO, KEGG, COG and BLASTX using nr protein database was performed. This revealed the upregulation of genes involved in various biological processes including ROS homeostasis, ion transport, signal transduction, ABA biosynthesis and osmoregulation. Genes encoding expansin, xyloglucan endotransglucosylase/hydrolase, dehydrins and peroxidases that take part in enhancement of root growth were found to be upregulated under salinity. This could be the reason for better root growth of Kharchia Local under long-term salinity stress as compared to its susceptible counterpart. The present investigation provides primary information on transcriptome profiling of Kharchia Local roots under long-term salinity stress at the anthesis stage. In conclusion, the data generated in this study provide useful insights in understanding the molecular mechanism of salinity stress tolerance and will also serve as a valuable genomic reservoir for functional characterization of salinity responsive genes to develop tolerant genotypes.

Heterologous Expression of a Novel Zoysia japonica C2H2 Zinc Finger Gene, ZjZFN1, Improved Salt Tolerance in Arabidopsis.

Growing evidence indicates that some grass species are more tolerant to various abiotic and biotic stresses than many crops. Zinc finger proteins play important roles in plant abiotic and biotic stresses. Although genes coding for these proteins have been cloned and identified in various plants, their function and underlying transcriptional mechanisms in the halophyte Zoysia japonica are barely known. In the present study, ZjZFN1 was isolated from Z. japonica using RACE method. Quantitative real time PCR results revealed that the expression of ZjZFN1 was much higher in leaf than in root and stem tissues, and induced by salt, cold or ABA treatment. The subcellular localization assay demonstrated that ZjZFN1 was localized to the nucleus. Expression of the ZjZFN1 in Arabidopsis thaliana improved seed germination and enhanced plant adaption to salinity stress with improved percentage of green cotyledons and growth status under salinity stress. Physiological and transcriptional analyses suggested that ZjZFN1 might, at least in part, influence reactive oxygen species accumulation and regulate the transcription of salinity responsive genes. Furthermore, RNA-sequencing analysis of ZjZFN1-overexpressing plants revealed that ZjZFN1 may serve as a transcriptional activator in the regulation of stress responsive pathways, including phenylalanine metabolism, α-linolenic acid metabolism and phenylpropanoid biosynthesis pathways. Taken together, these results provide evidence that ZjZFN1 is a potential key player in plants’ tolerance to salt stress, and it could be a valuable gene in Z. japonica breeding projects.

Roles of γ-aminobutyric acid on salinity-responsive genes at transcriptomic level in poplar: involving in abscisic acid and ethylene-signalling pathways.

γ-Aminobutyric acid (GABA) affected ABA and ethylene metabolic genes and signal components in salt-treated poplar, indicating its potential role in signal pathways of ABA and ethylene during salt stress. GABA is a small signalling molecule that accumulates rapidly in plants exposed to various stresses. However, the relationship between GABA and other signalling molecules, such as hormones, remains unclear. Here, in the poplar woody plant under 200-mM NaCl conditions, the application of low (0.25mM) and high (10mM) exogenous GABA, compared to 0mM, affected the accumulation of hydrogen peroxide and hormones, including ABA and ethylene, in different manners. Transcriptomic analysis demonstrated that 1025 differentially expressed genes (DEGs; |log2Ratio| ≥ 1.5) were widely affected by exogenous GABA under salt stress. A clustering analysis revealed that GABA could rescue or promote the effects of salt stress on gene expression. Among them, 146 genes involved in six hormone-signalling pathways were enriched, including 22 ABA- and 50 ethylene-related genes. Quantitative expression of selected genes involved in hormone-related pathways showed that ABA metabolic genes (ABAG, ABAH2, and ABAH4), ethylene biosynthetic genes (ACO1, ACO2, ACO5, ACOH1, ACS1, and ACS7) and receptor genes (PYL1, PYL2, PYL4, and PYL6) were regulated by exogenous GABA, even at a 0.1mM level. The production of ABA was negatively correlated with ABAH expression levels at different GABA concentrations. The increase of endogenous GABA, resulting from inhibitor (succinyl phosphonate) of α-ketoglutarate dehydrogenase, affected the PYLs levels. Thus, GABA may be involved in ABA- and ethylene-signalling pathways. Our data provide a better understanding of GABA's roles in the plant responses to environmental stresses.

Differential DNA methylation and transcription profiles in date palm roots exposed to salinity.

As a salt-adaptive plant, the date palm (Phoenix dactylifera L.) requires a suitable mechanism to adapt to the stress of saline soils. There is growing evidence that DNA methylation plays an important role in regulating gene expression in response to abiotic stresses, including salinity. Thus, the present study sought to examine the differential methylation status that occurs in the date palm genome when plants are exposed to salinity, and to identify salinity responsive genes that are regulated by DNA methylation. To achieve these, whole-genome bisulfite sequencing (WGBS) was employed and mRNA was sequenced from salinity-treated and untreated roots. The WGBS analysis included 324,987,795 and 317,056,091 total reads of the control and the salinity-treated samples, respectively. The analysis covered about 81% of the total genomic DNA with about 40% of mapping efficiency of the sequenced reads and an average read depth of 17-fold coverage per DNA strand, and with a bisulfite conversion rate of around 99%. The level of methylation within the differentially methylated regions (DMRs) was significantly (p < 0.05, FDR ≤ 0.05) increased in response to salinity specifically at the mCHG and mCHH sequence contexts. Consistently, the mass spectrometry and the enzyme-linked immunosorbent assay (ELISA) showed that there was a significant (p < 0.05) increase in the global DNA methylation in response to salinity. mRNA sequencing revealed the presence of 6,405 differentially regulated genes with a significant value (p < 0.001, FDR ≤ 0.05) in response to salinity. Integration of high-resolution methylome and transcriptome analyses revealed a negative correlation between mCG methylation located within the promoters and the gene expression, while a positive correlation was noticed between mCHG/mCHH methylation rations and gene expression specifically when plants grew under control conditions. Therefore, the methylome and transcriptome relationships vary based on the methylated sequence context, the methylated region within the gene, the protein-coding ability of the gene, and the salinity treatment. These results provide insights into interplay among DNA methylation and gene expression, and highlight the effect of salinity on the nature of this relationship, which may involve other genetic and epigenetic players under salt stress conditions. The results obtained from this project provide the first draft map of the differential methylome and transcriptome of date palm when exposed to an abiotic stress.

IDENTIFICATION OF GENES UP-REGULATED IN RESPONSE TO LEAD EXPOSURE IN SUNFLOWER (Helianthus annuus L.)

In this study, Differential display reverse transcription (DDRT) technique was used to analyze differentially upregulated genes in Helianthus annuus in response to Pb exposure. Seeds of sunflower were germinated in lead contaminated soils and untreated plants were used as control. Twenty differentially expressed fragments were identified and characterized. The fragments were classified according to their expression levels. The significance of the function of the identified differentially expressed genes was discussed in relation to their possible roles as stress genes. Two fragments showed no significant homology with any database sequences in the GenBank. Results of the database sequence alignment identified two fragments showed homology to unclassified and unknown genes; two cDNA fragments show homology with salinity responsive genes, three fragments showed homology with drought responsive genes, one fragment showed homology with cold responsive gene, one fragment showed homology with oxidative responsive gene and one fragment showed homology with biotic stress resistance gene. More importantly, a fragment had significant homology with EST of Glycine max similar to serine/threonine-protein kinase gene, a fragment showed significant homology with EST of Arabidopsis thaliana putative anion transporter 2 (ANTR2) mRNA, a fragment had significant homology with EST of Helianthus annuus delta-12 oleate desaturase (FAD2- 2) gene, a fragment showed significant homology with EST of Dianthus caryophyllus putative MtN3-like protein mRNA, two fragments showed significant homology with EST for NADH dehydrogenase chain 3 (nad3) genes, a fragment had significant homology with EST from Volvox sp. similar to cytochrome oxidase subunit 1(CoxI) and a fragment showed significant homology with EST23 of Medicago truncatula MLP-like protein. These results implicate that several pathways are involved in the plant's response to Pb exposure which still needs to be elucidated further.

Evaluation of genetic diversity of cis-acting elements of Abscisic acid responsive element binding protein (ABRE-BP) in selected Sri Lankan rice varieties

Salinity is a major abiotic stress that affects rice cultivation. Osmotic stress caused by salinity activates tolerance mechanisms in rice. The Abscisic Acid Responsive Element Binding Protein (ABRE-BP), transcribes for a bZIP family transcription factor that binds to the cis-regulatory element Abscisic Acid Responsive Element (ABRE) at the promoter of downstream salinity responsive genes and regulates their expression. Hence, the study was focused on analyzing the nucleotide diversity of a region in ABRE-BP promoter. Analysis of the ABRE-BP sequences of 47 Sri Lankan rice varieties and two reference varieties retrieved from a public database revealed many insertions and deletions (INDELs) and single nucleotide polymorphisms (SNPs) in the promoter. Eleven, abiotic stress related cis-elements were identified, but none of the INDELs spanned over them. However, SNPs either deleted existing cis-elements or created new cis-elements. The salinity stress responsive elements, MYBCORE and GT1GMSCAM4 were detected in few varieties, and were not associated with salinity tolerance based on current available salinity ratings. The presence of SNPs in cis-elements clustered them to nine groups at 68% similarity. The DNA polymorphisms on stress responsive cis-acting elements did not show a strong association with the known salinity ratings of many varieties. Nevertheless, the presence of INDELs affects the relative distance between elements, and thus may alter the expression of the ABRE-BP that regulates downstream stress responsive genes.