Polysome-bound mRNAs and translational mechanisms regulate drought tolerance in rice

Plants evolved several acquired tolerance traits for drought stress adaptation to maintain the cellular homeostasis. Drought stress at the anthesis stage in rice affects productivity due to the inefficiency of protein synthesis machinery. The effect of translational mechanisms on different pathways involved in cellular tolerance plays an important role. We report differential responses of translation-associated mechanisms in rice using polysome bound mRNA sequencing at anthesis stage drought stress in resistant Apo and sensitive IR64 genotypes. Apo maintained higher polysomes with 60 S-to-40 S and polysome-to-monosome ratios which directly correlate with protein levels under stress. IR64 has less protein levels under stress due to defective translation machinery and reduced water potential. Many polysome-bound long non-coding RNAs (lncRNA) were identified in both genotypes under drought, influencing translation. Apo had higher levels of N6-Methyladenosine (m6A) mRNA modifications that contributed for sustained translation. Translation machinery in Apo could maintain higher levels of photosynthetic machinery-associated proteins in drought stress, which maintain gas exchange, photosynthesis and yield under stress. The protein stability and ribosome biogenesis mechanisms favoured improved translation in Apo. The phytohormone signalling and transcriptional responses were severely affected in IR64. Our results demonstrate that, the higher translation ability of Apo favours maintenance of photosynthesis and physiological responses that are required for drought stress adaptation.

Exogenous application of nanocarrier-mediated double-stranded RNA manipulates physiological traits and defence response against bacterial diseases

Stability and delivery are major challenges associated with exogenous double-stranded RNA (dsRNA) application into plants. We report the encapsulation and delivery of dsRNA in cationic poly-aspartic acid-derived polymer (CPP6) into plant cells. CPP6 stabilizes the dsRNAs during long exposure at varied temperatures and pH, and protects against RNase A degradation. CPP6 helps dsRNA uptake through roots or foliar spray and facilitates systemic movement to induce endogenous gene silencing. The fluorescence of Arabidopsis GFP-overexpressing transgenic plants was significantly reduced after infiltration with gfp-dsRNA-CPP6 by silencing of the transgene compared to plants treated only with gfp-dsRNA. The plant endogenous genes flowering locus T (FT) and phytochrome interacting factor 4 (PIF4) were downregulated by a foliar spray of ft-dsRNA-CPP6 and pif4-dsRNA-CPP6 in Arabidopsis, with delayed flowering and enhanced biomass. The rice PDS gene targeted by pds-dsRNA-CPP6 through root uptake was effectively silenced and plants showed a dwarf and albino phenotype. The NaCl-induced OsbZIP23 was targeted through root uptake of bzip23-dsRNA-CPP6 and showed reduced transcripts and seedling growth compared to treatment with naked dsRNA. The negative regulators of plant defence SDIR1 and SWEET14 were targeted through foliar spray to provide durable resistance against bacterial leaf blight disease caused by Xanthomonas oryzae pv. oryzae (Xoo). Overall, the study demonstrates that transient silencing of plant endogenous genes using polymer-encapsulated dsRNA provides prolonged and durable resistance against Xoo, which could be a promising tool for crop protection and for sustaining productivity.

Phenotyping and metabolome analysis reveal the role of AdoMetDC and Di19 genes in determining acquired tolerance to drought in rice

Water-saving attempts for rice cultivation often reduce yields. Maintaining productivity under drought is possible when rice genotypes are bred with improved metabolism and spikelet fertility. Although attempts have been made to introgress water mining and water use efficiency traits, combining acquired tolerance traits (ATTs), that is, specific traits induced or upregulated to better tolerate severe stress, appears equally important. In our study, we screened 90 rice germplasm accessions that represented the molecular and phenotypic variations of 851 lines of the 3 K rice panel. Utilising phenomics, we identified markers linked to ATTs through association analysis of over 0.2 million SNPs derived from whole-genome sequences. Propensity to respond to 'induction' stress varied significantly among genotypes, reflecting differences in cellular protection against oxidative stress. Among the ATTs, the hydroxyl radical and proline contents exhibited the highest variability. Furthermore, these significant variations in ATTs were strongly correlated with spikelet fertility. The 43 significant markers associated with ATTs were further validated using a different subset of contrasting genotypes. Gene expression studies and metabolomic profiling of two well-known contrasting genotypes, APO (tolerant) and IR64 (sensitive), identified two ATT genes: AdoMetDC and Di19. Our study highlights the relevance of polyamine biosynthesis in modulating ATTs in rice. Genotypes with superior ATTs and the associated markers can be effectively employed in breeding rice varieties with sustained spikelet fertility and grain yield under drought.

Engineering traits through CRISPR/cas genome editing in woody species to improve forest diversity and yield

Dangers confronting forest ecosystems are many and the strength of these biological systems is deteriorating, thus substantially affecting tree physiology, phenology, and growth. The establishment of genetically engineered trees into degraded woodlands, which would be adaptive to changing climate, could help in subsiding ecological threats and bring new prospects. This should not be resisted due to the apprehension of transgene dispersal in forests. Consequently, it is important to have a deep insight into the genetic structure and phenotypic limits of the reproductive capability of tree stands/population(s) to endure tolerance and survival. Importantly, for a better understanding of genes and their functional mechanisms, gene editing (GeEd) technology is an excellent molecular tool to unravel adaptation progressions. Therefore, GeEd could be harnessed for resolving the allelic interactions for the creation of gene diversity, and transgene dispersal may be alleviated among the population or species in different bioclimatic zones around the globe. This review highlights the potential of the CRISPR/Cas tools in genomic, transcriptomic, and epigenomic-based assorted and programmable alterations of genes in trees that might be able to fix the trait-specific gene function. Also, we have discussed the application of diverse forms of GeEd to genetically improve several traits, such as wood density, phytochemical constituents, biotic and abiotic stress tolerance, and photosynthetic efficiency in trees. We believe that the technology encourages fundamental research in the forestry sector besides addressing key aspects, which might fasten tree breeding and germplasm improvement programs worldwide.

Stacking herbicide detoxification and resistant genes improves glyphosate tolerance and reduces phytotoxicity in tobacco (Nicotiana tabacum L.) and rice (Oryza sativa L.)

Glyphosate residues retained in the growing meristematic tissues or in grains of glyphosate-resistant crops affect the plants physiological functions and crop yield. Removing glyphosate residues in the plants is desirable with no penalty on crop yield and quality. We report a new combination of scientific strategy to detoxify glyphosate that reduces the residual levels and improve crop resistance. The glyphosate detoxifying enzymes Aldo-keto reductase (AKR1) and mutated glycine oxidase (mGO) with different modes of action were co-expressed with modified EPSPS, which is insensitive to glyphosate in tobacco (Nicotiana tabacum L.) and rice (Oryza sativa L.). The transgenic tobacco plants expressing individual PsAKR1, mGO, CP4-EPSPS, combinations of PsAKR1:CP4EPSPS, PsAKR1:mGO, and multigene with PsAKR1: mGO: CP4EPSPS genes were developed. The bio-efficacy studies of in-vitro leaf regeneration on different concentrations of glyphosate, seedling bioassay, and spray on transgenic tobacco plants demonstrate that glyphosate detoxification with enhanced resistance. Comparative analysis of the transgenic tobacco plants reveals that double and multigene expressing transgenics had reduced accumulation of shikimic acid, glyphosate, and its primary residue AMPA, and increased levels of sarcosine were observed in all PsAKR1 expressing transgenics. The multigene expressing rice transgenics showed improved glyphosate resistance with yield maintenance. In summary, results suggest that stacking genes with two different detoxification mechanisms and insensitive EPSPS is a potential approach for developing glyphosate-resistant plants with less residual content.

Transcriptomic responses under combined bacterial blight and drought stress in rice reveal potential genes to improve multi-stress tolerance

BACKGROUND

The unprecedented drought and frequent occurrence of pathogen infection in rice is becoming more due to climate change. Simultaneous occurrence of stresses lead to more crop loss. To cope up multiple stresses, the durable resistant cultivars needs to be developed, by identifying relevant genes from combined biotic and abiotic stress exposed plants.

RESULTS

We studied the effect of drought stress, bacterial leaf blight disease causing Xanthomonas oryzae pv. oryzae (Xoo) pathogen infection and combined stress in contrasting BPT5204 and TN1 rice genotypes. Mild drought stress increased Xoo infection irrespective of the genotype. To identify relevant genes that could be used to develop multi-stress tolerant rice, RNA sequencing from individual drought, pathogen and combined stresses in contrasting genotypes has been developed. Many important genes are identified from resistant genotype and diverse group of genes are differentially expressed in contrasting genotypes under combined stress. Further, a meta-analysis from individual drought and Xoo pathogen stress from public domain data sets narrowed- down candidate differentially expressed genes. Many translation associated genes are differentially expressed suggesting their extra-ribosomal function in multi-stress adaptation. Overexpression of many of these genes showed their relevance in improving stress tolerance in rice by different scientific groups. In combined stress, many downregulated genes also showed their relevance in stress adaptation when they were over-expressed.

CONCLUSIONS

Our study identifies many important genes, which can be used as molecular markers and targets for genetic manipulation to develop durable resistant rice cultivars. Strategies should be developed to activate downregulated genes, to improve multi-stress tolerance in plants.

Functional role of formate dehydrogenase 1 (FDH1) for host and nonhost disease resistance against bacterial pathogens

Nonhost disease resistance is the most common type of plant defense mechanism against potential pathogens. In the present study, the metabolic enzyme formate dehydrogenase 1 (FDH1) was identified to associate with nonhost disease resistance in Nicotiana benthamiana and Arabidopsis thaliana. In Arabidopsis, AtFDH1 was highly upregulated in response to both host and nonhost bacterial pathogens. The Atfdh1 mutants were compromised in nonhost resistance, basal resistance, and gene-for-gene resistance. The expression patterns of salicylic acid (SA) and jasmonic acid (JA) marker genes after pathogen infections in Atfdh1 mutant indicated that both SA and JA are involved in the FDH1-mediated plant defense response to both host and nonhost bacterial pathogens. Previous studies reported that FDH1 localizes to mitochondria, or both mitochondria and chloroplasts. Our results showed that the AtFDH1 mainly localized to mitochondria, and the expression level of FDH1 was drastically increased upon infection with host or nonhost pathogens. Furthermore, we identified the potential co-localization of mitochondria expressing FDH1 with chloroplasts after the infection with nonhost pathogens in Arabidopsis. This finding suggests the possible role of FDH1 in mitochondria and chloroplasts during defense responses against bacterial pathogens in plants.

Novel small molecules targeting bZIP23 TF improve stomatal conductance and photosynthesis under mild drought stress by regulating ABA

Drought-induced abscisic acid (ABA) accumulation plays a key role in plant water relations by regulating stomatal movements. Although ABA helps in the survival of the plants, reduced carbon gain affects plant productivity. To improve crop productivity under mild drought stress conditions, it is necessary to manipulate ABA responses. Other research groups have used forward chemical genomics for the identification of ABA agonists and antagonists aiming to manipulate ABA biosynthesis and signalling. In the present study, we identified indolyl-ethyl amine and serotonin small molecules using a reverse chemical genomics approach, with these acting as potent inhibitors of ABA biosynthesis through transient regulation of bZIP23 transcription factor activity. In rice, wheat and soybean, each of the small molecules enhanced the germination of seeds, even in the presence of ABA. These molecules nullified the effect of ABA on intact and detached leaves, resulting in higher photosynthesis. Furthermore, these small molecules effectively reduced the transcription levels of bZIP23 targeting NCED4, PP2C49 and CO3 genes. Rice plants treated with the small molecules were found to have improved stomatal conductance, spikelet fertility and yield compared to untreated plants under mild drought stress conditions. Our results suggest that indolyl-ethyl amine and serotonin small molecules could be utilized to improve yield under mild drought conditions.

Metabolome profiling reveals impact of water limitation on grain filling in contrasting rice genotypes

Drought significantly decreases crop productivity, especially in high water consuming crops like rice. Grain filling is one of the important critical growth phases in rice and drought during this phase leads to significant reduction in yield. In this study, a comparison was made between IR64 (drought susceptible) and Apo (drought tolerant) rice genotypes to capture the response to water limitation (50% field capacity (FC)) compared with the control (100%FC) during grain filling. Plants were grown in a high-throughput phenomics facility for precise imposition of moisture stress during grain filling. Apo performed better in water limited conditions with lower reduction of photosynthetic rate and maintenance of lower leaf temperature than IR64. Days from sowing to maturity, spikelet fertility and seed weight were more impeded by water limitation in IR64 than in Apo. Unlike Apo, IR64 did not show any decrease in transpiration rate at 50%FC compared with 100%FC. Metabolomic profiling of spikelets at grain filling showed distinct effects of water limitation on accumulation of metabolites, especially in Apo. Secondary metabolism, mainly the phenylpropanoid pathway involved in scavenging mechanisms, was upregulated in Apo. Accumulation of most amino acids was significantly higher in IR64 than in Apo. Due to higher rates of photosynthesis under stress, most carbohydrates accumulated more in Apo than in IR64 at 50%FC. Sucrose transporters were significantly upregulated in water limited conditions especially in Apo. Overall, thanks to higher source capacity, more source to sink transport and better scavenging, Apo showed a lower reduction in yield than IR64.

Rapid genotyping of bacterial leaf blight resistant genes of rice using loop-mediated isothermal amplification assay

The use of resistant (R) genes is the most effective strategy to manage bacterial leaf blight (BLB) disease of rice. Several attempts were made to incorporate R genes into susceptible rice cultivars using marker-assisted backcross breeding (MABB). However, MABB relies exclusively on PCR for foreground selection of R genes, which requires expensive equipment for thermo-cycling and visualization of results; hence, it is limited to sophisticated research facilities. Isothermal nucleic acid amplification techniques such as loop-mediated isothermal amplification (LAMP) assay do not require thermo-cycling during the assay. Therefore, it will be the best alternative to PCR-based genotyping. In this study, we have developed a LAMP assay for the specific and sensitive genotyping of seven BLB resistance (R) genes viz., Xa1, Xa3, Xa4, Xa7, Xa10, Xa11, and Xa21 in rice. Gene-specific primers were designed for the LAMP assay. The LAMP assay was optimized for time, temperature, and template DNA concentration. For effective detection, incubation at 60 °C for 30 min was optimum for all seven R genes. A DNA intercalating dye ethidium bromide and a calorimetric dye hydroxynaphthol blue was used for result visualization. Further, sensitivity assay revealed that the LAMP assay could detect R genes at 100 fg of template DNA compared to 1 ng and 10 pg, respectively, in conventional PCR and q-PCR assays. The LAMP assay developed in this study provides a simple, specific, sensitive, robust, and cost-effective method for foreground selection of R genes in the resistance breeding programs of resource-poor laboratory.

First record of off-season flowering in Populus deltoides from India: paradigm of climate change indicator

Populus deltoides is a fast-growing woody species possessing plethora of industrial applications. This species evolutionarily developed unisexual male and female catkin inflorescence on separate trees. Flowering usually occurs during early spring before the development of foliage, where buds appear near axils or at the extending shoots. In 2019, surveys were undertaken to study the flowering pattern of P. deltoides in the states of Punjab, Haryana, Uttar Pradesh and Uttarakhand in northern India. Interestingly, an anomalous flowering behaviour (appearance of off-season male catkins during autumn, i.e. October) was observed in a plantation trial at Kapurthala, Punjab. The male catkins were 2.7-3.1 ± 0.07 cm long and 0.3-0.5 ± 0.03 cm wide, which is significant for flowering and liberation of pollen grains. Preliminary results suggested that climatic factors, such as episodes of high or low temperature and the precipitation variation forcing the tree species to behave differently. Unearthing the climate-driven off-season flowering in other tree species alluded the stimulation of phytohormones, such as gibberellic and salicylic acid concentrations influencing the flowering time, therefore, needs further investigation in case of P. deltoides. Overall, this work provides early clues of changing climatic scenario altering the flowering pattern of a tropical forestry tree species.

Acquired Traits Contribute More to Drought Tolerance in Wheat Than in Rice

Drought tolerance is governed by constitutive and acquired traits. Combining them has relevance for sustaining crop productivity under drought. Mild levels of stress induce specific mechanisms that protect metabolism when stress becomes severe. Here, we report a comparative assessment of "acquired drought tolerance (ADT)" traits in two rice cultivars, IR64 (drought susceptible) and Apo (tolerant), and a drought-tolerant wheat cultivar, Weebill. Young seedlings were exposed to progressive concentrations of methyl viologen (MV), a stress inducer, before transferring to a severe concentration. "Induced" seedlings showed higher tolerance and recovery growth than seedlings exposed directly to severe stress. A novel phenomic platform with an automated irrigation system was used for precisely imposing soil moisture stress to capture ADT traits during the vegetative stage. Gradual progression of drought was achieved through a software-controlled automated irrigation facility. This facility allowed the maintenance of the same level of soil moisture irrespective of differences in transpiration, and hence, this platform provided the most appropriate method to assess ADT traits. Total biomass decreased more in IR64 than in Apo. The wheat cultivar showed lower levels of damage and higher recovery growth even compared to Apo. Expression of ROS-scavenging enzymes and drought-responsive genes was significantly higher in Apo than in IR64, but differences were only marginal between Apo and Weebill. The wheat cultivar showed significantly higher stomatal conductance, carbon gain, and biomass than the rice cultivars, under drought. These differences in ADT traits between cultivars as well as between species can be utilised for improving drought tolerance in crop plants.

Cross-Talk Signaling in Rice During Combined Drought and Bacterial Blight Stress

Due to climatic changes, rice crop is affected by moisture deficit stress and pathogens. Tissue water limitation besides reducing growth rates, also renders the crop susceptible to the infection by Xanthomonas oryzae pv. oryzae (Xoo) that causes bacterial leaf blight. Independently, both drought adaptation and Xoo resistance have been extensively studied. Though the cross-talk between drought and Xoo stress responses have been explored from individual stress studies, examining the combinatorial stress response is limited in rice. Recently published combined stress studies showed that under the combined stress, maintenance of carbon assimilation is hindered and such response is regulated by overlapping cellular mechanisms that are different from either of the individual stresses. Several receptors, MAP kinases, transcription factors, and ribosomal proteins, are predicted for playing a role in cellular homeostasis and protects cells from combined stress effects. Here we provide a critical analysis of these aspects using information from the recently published combined stress literature. This review is useful for researchers to comprehend combinatorial stress response of rice plants to drought and Xoo.

Aldo-ketoreductase 1 (AKR1) improves seed longevity in tobacco and rice by detoxifying reactive cytotoxic compounds generated during ageing

BACKGROUND

Maintenance of seed viability is an important factor for seedling vigour and plant establishment. Lipid peroxidation mediated reactive carbonyl compounds (RCC's) and non-enzymatic modifications of proteins through Maillard and Amadori products reduce seed viability and seedling vigour.

RESULTS

In this study, the relevance of RCCs on genotypic variation in rice seed viability and overexpression of an aldo-ketoreductase (AKR1) enzyme that detoxify cytotoxic compounds to improve seed viability and vigour was studied. Physiological and biochemical approaches were integrated to quantify the variation in seed viability and seedling vigour in rice genotypes after exposing to ageing treatment. AKR1 was overexpressed in a susceptible rice genotype and tobacco to study the relevance of reduced RCC's on seed viability and seedling vigour. The glycation and lipid peroxidation compounds accumulated after accelerated ageing treatments in rice genotypes. The accumulation of malondialdehyde, methyl glyoxal, Maillard and Amadori products affected the seed viability and germination as they showed a significant negative relationship. The transgenic rice and tobacco seeds expressing AKR1 showed lower levels of cytotoxic compounds and glycation products that resulted in improved seed viability and seedling vigour in rice and tobacco.

CONCLUSIONS

The study demonstrates that, reactive cytotoxic compounds affect the seed viability during storage. Detoxification of reactive cytotoxic compounds by Aldo-keto reductases is one of the mechanisms to improve the seed longevity during storage.

Quantification of Membrane Damage/Cell Death Using Evan's Blue Staining Technique

Membrane damage is a hallmark of both biotic and abiotic stress responses. The membrane determines the ability of a cell to sustain altered environmental conditions and hence can be used as a biomarker to assess stress-induced cell damage or death. We present an easy, quick, cost-effective, staining and spectrophotometric method to assess membrane stability of plant cells. In this method, Evan's blue, an azo dye, is used to assay for cell viability. More specifically, Evan's blue dye can penetrate through ruptured or destabilized membranes and stain cells. Thus, when plant cells are subjected to stress that compromises membrane integrity, the number of cells that are permeated by Evan's blue dye will be increased compared to control cells that are not stressed. In contrast, live, healthy cells that are capable of maintaining membrane integrity do not take up Evan's blue dye. Cells that have taken up Evan's blue dye will have an accumulation of a blue protoplasmic stain and these stained cells can be qualitatively documented under bright field microscopy with or without the use of a camera. Furthermore, the dye can be extracted from cells that are stained by Evan's blue dye and can be quantified spectrophotometrically. Using this analysis, the accumulation of dye in positively-stained cells correlates with the extent of cell membrane damage and thus the amount of cells that are stained with Evan's blue dye under various conditions can be used as an indicator of cellular stress.

Aldo-keto reductase enzymes detoxify glyphosate and improve herbicide resistance in plants

In recent years, concerns about the use of glyphosate-resistant crops have increased because of glyphosate residual levels in plants and development of herbicide-resistant weeds. In spite of identifying glyphosate-detoxifying genes from microorganisms, the plant mechanism to detoxify glyphosate has not been studied. We characterized an aldo-keto reductase gene from Pseudomonas (PsAKR1) and rice (OsAKR1) and showed, by docking studies, both PsAKR1 and OsAKR1 can efficiently bind to glyphosate. Silencing AKR1 homologues in rice and Nicotiana benthamiana or mutation of AKR1 in yeast and Arabidopsis showed increased sensitivity to glyphosate. External application of AKR proteins rescued glyphosate-mediated cucumber seedling growth inhibition. Regeneration of tobacco transgenic lines expressing PsAKR1 or OsAKRI on glyphosate suggests that AKR can be used as selectable marker to develop transgenic crops. PsAKR1- or OsAKRI-expressing tobacco and rice transgenic plants showed improved tolerance to glyphosate with reduced accumulation of shikimic acid without affecting the normal photosynthetic rates. These results suggested that AKR1 when overexpressed detoxifies glyphosate in planta.

Aldo-keto reductase-1 (AKR1) protect cellular enzymes from salt stress by detoxifying reactive cytotoxic compounds

Cytotoxic compounds like reactive carbonyl compounds such as methylglyoxal (MG), melandialdehyde (MDA), besides the ROS accumulate significantly at higher levels under salinity stress conditions and affect lipids and proteins that inhibit plant growth and productivity. The detoxification of these cytotoxic compounds by overexpression of NADPH-dependent Aldo-ketoreductase (AKR1) enzyme enhances the salinity stress tolerance in tobacco. The PsAKR1 overexpression plants showed higher survival and chlorophyll content and reduced MDA, H2O2, and MG levels under NaCl stress. The transgenic plants showed reduced levels of Na+ levels in both root and shoot due to reduced reactive carbonyl compounds (RCCs) and showed enhanced membrane stability resulted in higher root growth and biomass. The increased levels of antioxidant glutathione and enhanced activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) suggest AKR1 could protect these enzymes from the RCC induced protein carbonylation by detoxification process. The transgenics also showed higher activity of delta 1-pyrroline-5- carboxylate synthase (P5CS) enzyme resulted in increasedproline levels to maintain osmotic homeostasis. The results demonstrates that the AKR1 protects proteins or enzymes that are involved in scavenging of cytotoxic compounds by detoxifying RCCs generated under salinity stress.

Overexpression of EcbHLH57 Transcription Factor from Eleusine coracana L. in Tobacco Confers Tolerance to Salt, Oxidative and Drought Stress

Basic helix-loop-helix (bHLH) transcription factors constitute one of the largest families in plants and are known to be involved in various developmental processes and stress tolerance. We report the characterization of a stress responsive bHLH transcription factor from stress adapted species finger millet which is homologous to OsbHLH57 and designated as EcbHLH57. The full length sequence of EcbHLH57 consisted of 256 amino acids with a conserved bHLH domain followed by leucine repeats. In finger millet, EcbHLH57 transcripts were induced by ABA, NaCl, PEG, methyl viologen (MV) treatments and drought stress. Overexpression of EcbHLH57 in tobacco significantly increased the tolerance to salinity and drought stress with improved root growth. Transgenic plants showed higher photosynthetic rate and stomatal conductance under drought stress that resulted in higher biomass. Under long-term salinity stress, the transgenic plants accumulated higher seed weight/pod and pod number. The transgenic plants were also tolerant to oxidative stress and showed less accumulation of H202 and MDA levels. The overexpression of EcbHLH57 enhanced the expression of stress responsive genes such as LEA14, rd29A, rd29B, SOD, APX, ADH1, HSP70 and also PP2C and hence improved tolerance to diverse stresses.

Stable expression of mtlD gene imparts multiple stress tolerance in finger millet

Finger millet is susceptible to abiotic stresses, especially drought and salinity stress, in the field during seed germination and early stages of seedling development. Therefore developing stress tolerant finger millet plants combating drought, salinity and associated oxidative stress in these two growth stages is important. Cellular protection through osmotic adjustment and efficient free radical scavenging ability during abiotic stress are important components of stress tolerance mechanisms in plants. Mannitol, an osmolyte, is known to scavenge hydroxyl radicals generated during various abiotic stresses and thereby minimize stress damage in several plant species. In this study transgenic finger millet plants expressing the mannitol biosynthetic pathway gene from bacteria, mannitol-1-phosphate dehydrogenase (mtlD), were developed through Agrobacterium tumefaciens-mediated genetic transformation. mtlD gene integration in the putative transgenic plants was confirmed by Southern blot. Further, performance of transgenic finger millet under drought, salinity and oxidative stress was studied at plant level in T1 generation and in T1 and T2 generation seedlings. Results from these experiments showed that transgenic finger millet had better growth under drought and salinity stress compared to wild-type. At plant level, transgenic plants showed better osmotic adjustment and chlorophyll retention under drought stress compared to the wild-type. However, the overall increase in stress tolerance of transgenics for the three stresses, especially for oxidative stress, was only marginal compared to other mtlD gene expressing plant species reported in the literature. Moreover, the Agrobacterium-mediated genetic transformation protocol developed for finger millet in this study can be used to introduce diverse traits of agronomic importance in finger millet.