Porteresia Research Articles

A vacuolar antiporter is differentially regulated in leaves and roots of the halophytic wild rice Porteresia coarctata (Roxb.) Tateoka.

Vacuolar NHX-type antiporters play a role in Na(+)/K(+) uptake that contributes to growth, nutrition and development. Under salt/osmotic stress they mediate the vacuolar compartmentalization of K(+)/Na(+), thereby preventing toxic Na(+)K(+) ratios in the cytosol. Porteresia coarctata (Roxb.) Tateoka, a mangrove associate, is a distant wild relative of cultivated rice and is saline as well as submergence tolerant. A vacuolar NHX homolog isolated from a P. coarctata cDNA library (PcNHX1) shows 96 % identity (nucleotide level) to OsNHX1. Diurnal PcNHX1 expression in leaves was found to be largely unaltered, though damped by salinity. PcNHX1 promoter directed GUS expression is phloem-specific in leaves, stem and roots of transgenic plants in the absence of stress. Under NaCl stress, GUS expression was also seen in the epidermal and sub-epidermal layers (mesophyll, guard cells and trichomes) of leaves, root tip. The salinity in the rhizosphere of P. coarctata varies considerably due to diurnal/semi-diurnal tidal inundation. The diurnal expression of PcNHX1 in leaves and salinity induced expression in roots may have evolved in response to dynamic changes in salinity of in the P. coarctata rhizosphere. Despite high sequence conservation between OsNHX1 and PcNHX1, the distinctive expression pattern of PcNHX1 exemplifies how variation in expression is fine tuned to suit the halophytic growth habitat of a plant.

Assessment of genetic diversity in salt-tolerant rice and its wild relatives for ten SSR loci and one allele mining primer of salT gene located on 1st chromosome

A heterogeneous collection of rice genotypes which included seven salt-tolerant rice lines, one salt-sensitive improved line, one wild rice (Oryza rufipogon) and one salt-tolerant wild rice relative (Porteresia coarctata) was screened with ten salt-tolerance-linked simple sequence repeat markers, of which nine were from the Saltol QTL mapped on rice 1st chromosome and the rest one from 8th chromosome, having high phenotypic variance for salt tolerance. Variation in molecular weight (in the form of base pairs) of the different amplified products using RM primers was used to find out the genetic relationship among the studied rice genotypes. Genomic DNA of the studied genotypes was also amplified with a reported allele mining primer for a salt-inducible gene (salT). The amplified products were sequenced and aligned to find out the closeness among the rice lines for the studied gene. Dendrogram derived from marker profiles showed partial similarity with salT gene-derived tree. Commonly, all the salt-tolerant lines were grouped into a single cluster, including IR36 (a salt-sensitive line) to which O. rufipogon (the wild rice) and P. coarctata (the wild rice relative) joined separately. The taxonomic identity and evolutionary relationship among the three groups (rice, wild rice and wild rice relative) were bioinformatically analysed using the nucleotide sequence of the studied salT gene.

Deep Transcriptome Sequencing of Wild Halophyte Rice, Porteresia coarctata, Provides Novel Insights into the Salinity and Submergence Tolerance Factors

Porteresia coarctata is a wild relative of rice with capability of high salinity and submergence tolerance. The transcriptome analyses of Porteresia can lead to the identification of candidate genes involved in salinity and submergence tolerance. We sequenced the transcriptome of Porteresia under different conditions using Illumina platform and generated about 375 million high-quality reads. After optimized assembly, a total of 152 367 unique transcript sequences with average length of 794 bp were obtained. Many of these sequences might represent fragmented transcripts. Functional annotation revealed the presence of genes involved in diverse cellular processes and 2749 transcription factor (TF)-encoding genes in Porteresia. The differential gene expression analyses identified a total of 15 158 genes involved in salinity and/or submergence response(s). The stress-responsive members of different TF families, including MYB, bHLH, AP2-EREBP, WRKY, bZIP and NAC, were identified. We also revealed key metabolic pathways, including amino acid biosynthesis, hormone biosynthesis, secondary metabolite biosynthesis, carbohydrate metabolism and cell wall structures, involved in stress tolerance in Porteresia. The transcriptome analyses of Porteresia are expected to highlight genes/pathways involved in salinity and submergence tolerance of this halophyte species. The data can serve as a resource for unravelling the underlying mechanism and devising strategies to engineer salinity and submergence tolerance in rice.

Cloning, characterization and expression of a chloroplastic fructose-1,6-bisphosphatase from Porteresia coarctata conferring salt-tolerance in transgenic tobacco

A gene coding for the chloroplastic fructose 1,6-bisphosphatase (PcCFR) in Porteresia coarctata Tateoka (Roxb.), a halophytic wild rice, has been isolated along with its rice (Oryza sativa; var. indica) homologue (OsCFR), cloned and sequenced. Comparison between the nucleotide and deduced amino acid sequences of these two revealed a difference in five amino acid residues, namely Glu14, Thr24, Ala48, Ala163 and Arg296 in OsCFR which have been found to be replaced by Ser14, Ile24, Ser48, Ser163 and Lys296 in PcCFR respectively. The purified recombinant PcCFR is found to retain its enzymatic activity in presence of up to 500 mM NaCl in vitro as opposed to OsCFR, which is inactivated even at lower salt concentration. The six in vitro point mutant proteins of PcCFR showed varied degree of sensitivity towards high salt, with the maximum OsCFR-like effect in the triple mutant S14A-S48A-S163A suggesting a possible concerted role of all three serine residues in the in vitro salt tolerance property of PcCFR protein. Transgenic tobacco plants with chloroplast targeted PcCFR and OsCFR gene(s) have been developed under constitutive expression of CaMV 35S promoter and NOS terminator. The PcCFR transgenics showed better plant growth during exposure to salt stress in comparison to either the OsCFR or the empty vector transformed plants. The PcCFR transgenics also revealed enhanced photosynthetic efficiency coupled with protection to both photodamage of PSII and chlorophyll degradation through better reactive oxygen species scavenging at higher concentration of NaCl during late salt-stress growth.

Targeted expression of L-myo- inositol 1-phosphate synthase from Porteresia coarctata (Roxb.) Tateoka confers multiple stress tolerance in transgenic crop plants

Improving crop tolerance to osmotic stresses is a longstanding goal of agricultural biotechnology. In the present work the PcINO1 gene coding for a salt-tolerant L-myo-inositol-1-phosphate synthase (MIPS) from Porteresia coarctata (Roxb.) Tateoka, a halophytic wild rice was introgressed into cultivated mustard, Brassica juncea var B85. The transgenic plants demonstrate increased tolerance to salinity and oxidative stress with elevated level of inositol in both roots and shoots. The yield and crop quality of transgenic Brassica plants remain uncompromised and the plants were able to stably grow, set seeds and germinate in saline environments. When targeted to seeds of Nicotiana, PcINO1 was able to improve the seed survival rate under salinity and dehydration. Inositol and its derivatives regulate stress responses in various ways, serving as compatible solutes or signaling molecules. It is implicated that engineering inositol metabolism may affect the plant metabolic network leading to a stress tolerant phenotype as enumerated here in transgenic crop plants. How inositol itself or its derivatives affect the overall metabolic pathways leading to a stress-tolerant phenotype remains an intriguing question for future investigations.

5′ Regulatory region of ubiquitin 2 gene from Porteresia coarctata makes efficient promoters for transgene expression in monocots and dicots

Porteresia ubiquitin 5' regulatory region drives transgene expression in monocots and dicots. Ubiquitin promoters are promising candidates for constitutive transgene expression in plants. In this study, we isolated and characterized a novel 5' regulatory sequence of a ubiquitin gene from Porteresia coarctata, a stress-tolerant wild grass species. Through functional analysis in heterologous plant systems, we have demonstrated that full length (Port Ubi2.3) or truncated sequence (PD2) of the isolated regulatory fragment can drive constitutive expression of GUS in monocots and/or dicots. In silico analysis of Port Ubi2.3 has revealed the presence of a 640bp core promoter region followed by two exons and two introns with numerous putative cis-acting sites scattered throughout the regulatory region. Transformation and expression studies of six different deletion constructs in rice, tobacco and sugarcane revealed that the proximal intron has an enhancing effect on the activity of the core promoter in both monocots and dicots, whereas, Port Ubi2.3 was able to render strong expression only in monocots. This regulatory sequence is quite distinct from the other reported ubiquitin promoters in structure and performs better in monocots compared to other commonly used promoters-maize Ubi1 and Cauliflower Mosaic Virus 35S.

Plant proteome responses to salinity stress - comparison of glycophytes and halophytes.

The review discusses impacts of salinity on proteome composition in both salinity-sensitive (glycophytic) and salinity-tolerant (halophytic) plants. Salinity response with respect to proteome changes is compared in glycophytes and halophytes with a special focus on specific strategies employed by halophytes to cope with high (above 200mM NaCl) salt concentrations. The results of comparative proteomic studies aimed at determination of the differences in salinity response between related plant species with contrasting salinity tolerance (Arabidopsis thaliana vs Thellungiella salsuginea, common wheat vs its hybrid, rice vs Porteresia coarctata) are analysed. The comparative studies have revealed that salt-tolerant plants display an enhanced constitutive expression of several salt-responsive genes and fewer salinity-related disturbances in energy metabolism with respect to the salt-sensitive plants. In conclusion, recent results of comparative proteomic studies are summarised and possible ways of utilisation of the obtained results for an improvement of plant (crop) salt tolerance are discussed.

Genetic profiling of a small heterogeneous population presenting traditional, wild and wild relatives of rice (Oryza saliva L.) in relation to osmotic stress tolerance

Biochemical and genetic profiling of five rice lines which included one high yielding drought and salt sensitive cultivar (IR36), one drought avoiding indigenous line (Gorah), one salt tolerant popular cultivar (Nona Bokra), one wild rice (Oryza rufipogon) and one wild halophytic rice relative (Porteresia coarctata) were done in relation to osmotic stress tolerance. Biochemical analyses were done for three compounds (proline content, total chlorophyll and total protein) which are quantitatively vary under different osmotic stresses. The rice lines were genotyped for seven osmotic stress tolerance linked rice SSR loci and DNA sequence analysis was done for the amplified product of a salt inducible gene (salT) using two sets of allele mining primers. The varied biochemical profiles and growth habitat of the studied rice lines were partially confirmed both by the fingerprint analysis using rice SSRS (Simple Sequence Repeats) and DNA sequence analysis of the amplified product for the selected salt inducible gene.

Seasonal changes in Porteresia coarctata (Tateoka) beds along a subtropical coast

Shoot density, standing crop (above- and below-ground biomass) and habitat of salt marsh grass Porteresia coarctata were investigated along the coast of Bakkhali estuary, Cox’s Bazar, Bangladesh from January to December 2006. Shoot density of P. coarctata was influenced by season and was found to be higher (>2 500 shoots/m2) in post-monsoon and minimal in monsoon season; plants were particularly active in vegetative propagation during pre-monsoon. Above-ground biomass was greater along the protected coast compared with the exposed one in this estuary. Below-ground biomass was higher (7.75–269.53 g DW/m2) than that above ground (2.20–114.75 g DW/m2). Standing crops of P. coarctata showed a negative relationship (R =−0.77; P <0.05) with sedimentation rate, while seasonal activity influenced sedimentation. The recorded sedimentation rate was lower (6.09 mg/(cm2·d)) in pre-monsoon and highest (14.55 mg/(cm2·d)) in monsoon season. The mean value of pore water salinity was higher (34.25±5.05) during post-monsoon and lowest (18.0±3.71) in monsoon season. The soil was sandy clay in this P. coarctata bed; it consisted of 86% sand, 13% clay and 1% silt. Soil organic matter dropped during the monsoon season (0.78%–0.67%) and was highest ((2.17±1.42)%–(2.3±1.47)%) during post-monsoon, probably owing to accumulation of decomposed peat on the marsh surface. The mean pore water NH4-N concentration ranged from 2.44±1.65 to 3.33±1.82 μg/L, with a minimum air temperature of 22.09°C in post-monsoon and a maximum of 31.16°C in pre-monsoon. Variations of physico-chemical parameters in the soil, water, and climate governed biological parameters of P. coarctata in the Bakkhali estuary, and were comparable with estuarine environments elsewhere.

Isolation and Characterization of Antibacterial Compound from a Mangrove-Endophytic Fungus, Penicillium chrysogenum MTCC 5108.

Microorganisms, especially endophytic fungi that reside in the tissue of living mangrove plants, seem to play a major role in meeting the general demand for new biologically active substances. During the course of screening for biologically active secondary metabolites from marine microorganisms, an antibiotic compound containing an indole and a diketopiperazine moiety was isolated from the culture medium of Penicillium chrysogenum, (MTCC 5108), an endophytic fungus on the mangrove plant Porteresia coarctata (Roxb.). The cell free culture medium of P. chrysogenum showed significant activity against Vibrio cholerae, (MCM B-322), a pathogen causing cholera in humans. Bioassay guided chemical characterization of the crude extract led to the isolation of a secondary metabolite possessing a molecular formula C19H21O2N3. Its antibacterial activity was comparable with standard antibiotic, streptomycin. This compound (1) was found to be (3,1'-didehydro-3[2″(3'″,3'″-dimethyl-prop-2-enyl)-3″-indolylmethylene]-6-methyl pipera-zine-2,5-dione) on the basis of mass spectrometry, infrared spectroscopy and one and two-dimensional nuclear magnetic resonance analysis.

Phylogenetic study of Oryzoideae species and related taxa of the Poaceae based on atpB-rbcL and ndhF DNA sequences

Oryzoideae (Poaceae) plants have economic and ecological value. However, the phylogenetic position of some plants is not clear, such as Hygroryza aristata (Retz.) Nees. and Porteresia coarctata (Roxb.) Tateoka (syn. Oryza coarctata). Comprehensive molecular phylogenetic studies have been carried out on many genera in the Poaceae. The different DNA sequences, including nuclear and chloroplast sequences, had been extensively employed to determine relationships at both higher and lower taxonomic levels in the Poaceae. Chloroplast DNA ndhF gene and atpB-rbcL spacer were used to construct phylogenetic trees and estimate the divergence time of Oryzoideae, Bambusoideae, Panicoideae, Pooideae and so on. Complete sequences of atpB-rbcL and ndhF were generated for 17 species representing six species of the Oryzoideae and related subfamilies. Nicotiana tabacum L. was the outgroup species. The two DNA datasets were analyzed, using Maximum Parsimony and Bayesian analysis methods. The molecular phylogeny revealed that H. aristata (Retz.) Nees was the sister to Chikusichloa aquatica Koidz. Moreover, P. coarctata (Roxb.) Tateoka was in the genus Oryza. Furthermore, the result of evolution analysis, which based on the ndhF marker, indicated that the time of origin of Oryzoideae might be 31 million years ago.

Characterization of a type 3 metallothionein isolated from Porteresia coarctata

Metallothioneins are involved in detoxification of heavy metals. A cDNA encoding type 3 metallothionein (PcMT3) was isolated from the salt stressed leaf cDNA library of Porteresia coarctata (Roxb.) Tateoka (wild rice) that grows well in the heavy metal laden estuarine soils. The PcMT3 cDNA (581 bp) encodes a protein of 64 amino acids. PcMT3 is highly homologous (82 %) to OsMT-I-3a of rice, but is unique from other type 3 plant MTs due to the presence of an additional glycine residue in the C-terminal domain. Analysis of the 5′ upstream region of PcMT3 showed the presence of cis-acting elements like the CG box and STRE previously reported to be involved in gene expression under heavy metal stress. Southern analysis suggested the presence of more than one copy of PcMT3-like sequences in the P. coarctata genome. Analysis of genomic clone of PcMT3 revealed the presence of two introns. A comparison of the genomic sequence of PcMT3 with closely similar type 3 MTs from rice and mangrove species revealed conservation in the number and position of introns. Transcript profiling for PcMT3 in P. coarctata leaves in the presence of Cd, Cu and Zn showed an increase in transcript accumulation.

Enhanced salt tolerance of transgenic tobacco plants by co-expression of PcINO1 and McIMT1 is accompanied by increased level of myo-inositol and methylated inositol

Introgression and functional expression of either the PcINO1 (L: -myo-inositol 1-phosphate synthase or MIPS coding gene from the wild halophytic rice, Porteresia coarctata) or McIMTI (inositol methyl transferase, IMTI coding gene from common ice plant Mesembryanthemum crystallinum) has earlier been shown to confer salt tolerance to transgenic tobacco plants (Sheveleva et al., Plant Physiol 115:1211-1219, 1997; Majee et al., J Biol Chem 279:28539-28552, 2004). In this communication, we show that transgenic tobacco plants co-expressing PcINO1 and McIMT1 gene either in cytosol or in chloroplasts accumulate higher amount of total inositol (free and methyl inositol) compared to non-transgenic plants. These transgenic plants were more competent in terms of growth potential and photosynthetic activity and were less prone to oxidative stress under salt stress. A positive correlation between the elevated level of total inositol and methylated inositol and the capability of the double transgenic plants to withstand a higher degree of salt stress compared to the plants expressing either PcINO1 or McIMT1 alone is inferred.

Vibrio mangrovi sp. nov., a diazotrophic bacterium isolated from mangrove-associated wild rice (Poteresia coarctata Tateoka)

The taxonomic status of a nitrogen-fixing bacterium, strain MSSRF38(T), isolated from the rhizosphere of mangrove-associated wild rice (Porteresia coarctata Tateoka), in Pichavaram, India, was studied using a polyphasic approach. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the novel strain MSSRF38(T) was most closely related to Vibrio ruber DSM 16370(T) (98.3% gene sequence similarity), Vibrio rhizosphaerae DSM 18581(T) (98.2% sequence similarity) and <96% to the remaining Vibrio species. Multilocus sequence analysis using ftsZ, gapA, gyrB and mreB genes showed low levels of gene sequence similarities (82-90%) with all species of the genus Vibrio with validly published names, indicating that strain MSSRF38(T) occupies a distinct phylogenetic position. DNA-DNA hybridization experiments showed that strain MSSRF38(T) had <70% DNA-DNA similarity to its closest neighbours V. ruber DSM 16370(T) (27.4%) and V. rhizosphaerae DSM 18581(T) (12.1%). Strain MSSRF38(T) could be differentiated from its relatives on the basis of several phenotypic characteristics. The major fatty acids were feature 3 (including C(16:1omega)7c and/or C(15:0) iso 2-OH), C16:0, C(18:1omega)7c, C(14:0) and C(12:0). The DNA G+C content was 45.4 mol%. Based on genotypic, phenotypic, chemotaxonomic and DNA-DNA analyses, the name Vibrio mangrovi sp. nov. (type strain MSSRF38(T)=LMG 24290(T)=DSM 19641(T)) is proposed for this novel taxon.

Identification and organization of chloroplastic and cytosolic l-myo-inositol 1-phosphate synthase coding gene(s) in Oryza sativa: comparison with the wild halophytic rice, Porteresia coarctata

The gene coding for rice chloroplastic L-myo-inositol-1-phosphate synthase (MIPS; EC 5.5.1.4) has been identified by matrix-assisted laser desorption time-of-flight mass spectrometry analysis of the purified and immunologically cross-reactive approximately 60 kDa chloroplastic protein following two-dimensional polyacrylamide gel electrophoresis, which exhibited sequence identity with the cytosolic MIPS coded by OsINO1-1 gene. A possible chloroplastic transit peptide sequence was identified upstream of the OsINO1-1 gene upon analysis of rice genome. RT-PCR and confocal microscope studies confirmed transcription, effective translation and its functioning as a chloroplast transit peptide. Bioinformatic analysis mapped the chloroplastic MIPS (OsINO1-1) gene on chromosome 3, and a second MIPS gene (OsINO1-2) on chromosome 10 which lacks conventional chloroplast transit peptide sequence as in OsINO1-1. Two new PcINO1 genes, with characteristic promoter activity and upstream cis-elements were identified and cloned, but whether these proteins can be translocated to the chloroplast or not is yet to be ascertained. Electrophoretic mobility shift assay carried out with nuclear extract of Porteresia coarctata leaves grown under both control and stressed condition shows binding of nuclear proteins with the upstream elements. Nucleotide divergence among the different Oryza and Porteresia INO1 genes were calculated and compared.

Porteresia coarctata (Roxb.) Tateoka, a wild rice: a potential model for studying salt‐stress biology in rice

Porteresia coarctata (Syn = Oryza coarctata) is a tetraploid wild rice growing abundantly in the coastal region of India and some other Asian countries. The salt tolerance property of this mangrove associate has been dealt with by a number of workers earlier. The distinct morphology and leaf architecture enabling the plant to exclude salt is a characteristic feature of Porteresia in comparison with Oryza sp. A number of genes have been isolated and characterized from Porteresia that are related to the salt-tolerance property of the plant. Evidence have accumulated that some pathways critical to salt tolerance are in operation in Porteresia of which the inositol metabolic pathway has been recently elaborated. Some of the enzymes of Porteresia have been shown to function as salt-tolerant under in vitro studies giving a clue that this wild halophytic rice may have evolved genes and proteins capable of functioning under a salt environment. Bioprospecting of such genes and proteins coupled with genomic and proteomic approaches remain an exciting area of research in evaluating this plant as a model for salt tolerance for the rice plant.

Mangrovibacter plantisponsor gen. nov., sp. nov., a nitrogen-fixing bacterium isolated from a mangrove-associated wild rice (Porteresia coarctata Tateoka)

A facultatively anaerobic, nitrogen-fixing bacterium, strain MSSRF40(T), was isolated from roots of mangrove-associated wild rice (Porteresia coarctata Tateoka). On the basis of 16S rRNA gene sequence similarities, strain MSSRF40(T) was shown to belong to the family Enterobacteriaceae, most closely related to Cronobacter muytjensii E603(T) (97.2 % sequence similarity), Enterobacter cloacae subsp. dissolvens LMG 2683(T) (97.1 %), E. radicincitans D5/23(T) (97.1 %) and E. ludwigii EN-119(T) (97.0 %). Sequence analysis of rpoB, gyrB and hsp60 genes showed that strain MSSRF40(T) had relatively low sequence similarity (<91, <84 and <90 %) to recognized species of different genera of the family Enterobacteriaceae and formed an independent phyletic lineage in all phylogenetic analyses using the 16S rRNA, rpoB, gyrB and hsp60 genes, clearly indicating that strain MSSRF40(T) could not be affiliated to any of the recognized genera within the family Enterobacteriaceae. The dominant cellular fatty acids were C(16 : 0), C(16 : 1)omega7c and/or iso-C(15 : 0) 2-OH and C(18 : 1)omega7c, similar to those of other members of the Enterobacteriaceae. The DNA G+C content was 50.1 mol%. Phylogenetic distinctiveness and phenotypic differences from its phylogenetic neighbours indicated that strain MSSRF40(T) represents a novel species and genus within the family Enterobacteriaceae, for which the name Mangrovibacter plantisponsor gen. nov., sp. nov. is proposed. The type strain of Mangrovibacter plantisponsor is strain MSSRF40(T) (=LMG 24236(T) =DSM 19579(T)).

Isolation and molecular characterization of genetically diverse antagonistic, diazotrophic red-pigmented vibrios from different mangrove rhizospheres

Genetic diversity of red-pigmented vibrios from different mangrove rhizospheres (Porteresia coarctata, Avicennia marina and Rhizophora mucronata) collected from Pichavaram mangrove, India was investigated. Twenty red-pink pigmented strains were isolated, 16S rRNA gene analyses indicted that these isolates belong to the genus Vibrio and were phylogenetically closely related to the type strains of Vibrio rhizosphaerae and Vibrio ruber. The rep-PCR analysis using GTG(5) and BOX primers had similar groupings, and segregated these pigmented Vibrio isolates including two type strains into seven unique genotypic groups (REP groups A1-A7). The rhizosphere of P. coarctata harbors highly genetically diverse groups of red-pigmented vibrios compared to other plants. Multilocus sequence analysis using four genetic loci (pyrH, recA, rpoA, 16S rRNA) clearly supported the hypothesis that strains MSSRF38 (REP group A5) and MSSRF39 (REP group A6) could represent new Vibrio species. Biological functions of these vibrios were also determined and it was found that all these isolates have antagonistic activity against phytopathogens, and isolates belonging to REP groups A5 and A6 were positive for nifH gene by PCR. In conclusion, this study for the first time demonstrates the occurrence of genetically diverse groups of antagonistic, diazotrophic red-pigmented vibrios from different mangrove plants and suggests a new ecological role for vibrios as heterotrophic plant associated rhizobacteria.

Insight into the salt tolerance factors of a wild halophytic rice, Porteresia coarctata: a physiological and proteomic approach

Salinity poses a serious threat to yield performance of cultivated rice in South Asian countries. To understand the mechanism of salt-tolerance of the wild halophytic rice, Porteresia coarctata in contrast to the salt-sensitive domesticated rice Oryza sativa, we have compared P. coarctata with the domesticated O. sativa rice varieties under salinity stress with respect to several physiological parameters and changes in leaf protein expression. P. coarctata showed a better growth performance and biomass under salinity stress. Relative water content was conserved in Porteresia during stress and sodium ion accumulation in leaves was comparatively lesser. Scanning electron microscopy revealed presence of two types of salt hairs on two leaf surfaces, each showing a different behaviour under stress. High salt stress for prolonged period also revealed accumulation of extruded NaCl crystals on leaf surface. Changes induced in leaf proteins were studied by two-dimensional gel electrophoresis and subsequent quantitative image analysis. Out of more than 700 protein spots reproducibly detected and analyzed, 60% spots showed significant changes under salinity. Many proteins showed steady patterns of up- or downregulation in response to salinity stress. Twenty protein spots were analyzed by MALDI-TOF, leading to identification of 16 proteins involved in osmolyte synthesis, photosystem functioning, RubisCO activation, cell wall synthesis and chaperone functions. We hypothesize that some of these proteins confer a physiological advantage on Porteresia under salinity, and suggest a pattern of salt tolerance strategies operative in salt-marsh grasses. In addition, such proteins may turn out to be potential targets for recombinant cloning and introgression in salt-sensitive plants.

Inositol methyl tranferase from a halophytic wild rice, Porteresia coarctata Roxb. (Tateoka): regulation of pinitol synthesis under abiotic stress

Methylated inositol D-pinitol (3-O-methyl-D-chiro-inositol) accumulates in a number of plants naturally or in response to stress. Here, we present evidence for accumulation and salt-enhanced synthesis of pinitol in Porteresia coarctata, a halophytic wild rice, in contrast to its absence in domesticated rice. A cDNA for Porteresia coarctata inositol methyl transferase 1 (PcIMT1), coding for the inositol methyl transferase implicated in the synthesis of pinitol has been cloned from P. coarctata, bacterially overexpressed and shown to be functional in vitro. In silico analysis confirms the absence of an IMT1 homolog in Oryza genome, and PcIMT1 is identified as phylogenetically remotely related to the methyl transferase gene family in rice. Both transcript and proteomic analysis show the up-regulation of PcIMT1 expression following exposure to salinity. Coordinated expression of L-myo-inositol 1-phosphate synthase (PcINO1) gene along with PcIMT1 indicates that in P. coarctata, accumulation of pinitol via inositol is a stress-regulated pathway. The presence of pinitol synthesizing protein/gene in a wild halophytic rice is remarkable, although its exact role in salt tolerance of P. coarctata cannot be currently ascertained. The enhanced synthesis of pinitol in Porteresia under stress may be one of the adaptive features employed by the plant in addition to its known salt-exclusion mechanism.