Isolation of a cDNA clone (PcSrp) encoding serine-rich-protein from Porteresia coarctata T. and its expression in yeast and finger millet (Eleusine coracana L.) affording salt tolerance

Milletomics: a metabolomics centered integrated omics approach toward genetic progression

Producing alternative staple foods like millet will be essential to feeding ten billion people by 2050. The increased demand for millet is driving researchers to improve its genetic variation. Millets include protein, dietary fiber, phenolic substances, and flavonoid components. Its climate resilience makes millet an appealing crop for agronomic sustainability. Integrative omics technologies could potentially identify and develop millets with desirable phenotypes that may have high agronomic value. Millets' salinity and drought tolerance have been enhanced using transcriptomics. In foxtail, finger, and pearl millet, proteomics has discovered salt-tolerant protein, phytohormone-focused protein, and drought tolerance. Metabolomics studies have revealed that certain metabolic pathways including those involving lignin, flavonoids, phenylpropanoid, and lysophospholipids are critical for many processes, including seed germination, photosynthesis, energy metabolism, and the synthesis of bioactive chemicals necessary for drought tolerance. Metabolomics integration with other omics revealed metabolome engineering and trait-specific metabolite creation. Integrated metabolomics and ionomics are still in the development stage, but they could potentially assist in comprehending the pathway of ionomers to control nutrient levels and biofortify millet. Epigenomic analysis has shown alterations in DNA methylation patterns and chromatin structure in foxtail and pearl millets in response to abiotic stress. Whole-genome sequencing utilizing next-generation sequencing is the most proficient method for finding stress-induced phytoconstituent genes. New genome sequencing enables novel biotechnological interventions including genome-wide association, mutation-based research, and other omics approaches. Millets can breed more effectively by employing next-generation sequencing and genotyping by sequencing, which may mitigate climate change. Millet marker-assisted breeding has advanced with high-throughput markers and combined genotyping technologies.

Finger millet (Eleusine coracana L.): from staple to superfood-a comprehensive review on nutritional, bioactive, industrial, and climate resilience potential

MAIN CONCLUSION

This review discusses the Finger millet's rich nutritional profile, bioactive potential, and industrial applications, combined with its climate resilience, which make it a promising crop for enhancing food security and promoting sustainable agriculture. This review also highlights its significant potential to address malnutrition and mitigate climate change impacts. The emergence of Finger millet from "poor man's staple food" to "a nutrient rich cereal" has encouraged the need to explore this crop at a wider scale. It is a highly significant crop due to its rich nutritional and bioactive profile, diverse biological activities, and promising industrial applications, along with the high climate resilience. This comprehensive review evaluates its nutritional composition by comparing favorably with other cereals and millets and emphasizing its potential to address malnutrition and enhance food security. Furthermore, it explores the phytochemical/bioactive potential and strategies to enhance their bioavailability followed biological activities of Finger millet by highlighting its various health-promoting properties. The review also discusses industrial potential of finger millet including its role in nutraceutical and functional food production, as well as bioenergy generation. In addition, role of Finger millet as a climate-resilient crop; specifically, the available genetic resources and identification of genes and quantitative trait loci (QTLs) associated with major stress tolerance traits have also been discussed. By providing a comprehensive synthesis of existing knowledge, this study offers valuable insights for researchers, policymakers, and stakeholders engaged in efforts to promote sustainable agriculture, enhance food and nutrition security, and mitigate the impacts of climate change.

The potentialities of omics resources for millet improvement

Millets are nutrient-rich (nutri-rich) cereals with climate resilience attributes. However, its full productive potential is not realized due to the lack of a focused yield improvement approach, as evidenced by the available literature. Also, the lack of well-characterized genomic resources significantly limits millet improvement. But the recent availability of genomic data and advancement in omics tools has shown its enormous potential to enhance the efficiency and precision faced by conventional breeding in millet improvement. The development of high throughput genotyping platforms based on next-generation sequencing (NGS) has provided a low-cost method for genomic information, specifically for neglected nutri-rich cereals with the availability of a limited number of reference genome sequences. NGS has created new avenues for millet biotechnological interventions such as mutation-based study, GWAS, GS, and other omics technologies. The simultaneous discovery of high-throughput markers and multiplexed genotyping platform has aggressively aided marker-assisted breeding for millet improvement. Therefore, omics technology offers excellent opportunities to explore and combine useful variations for targeted traits that could impart high nutritional value to high-yielding cultivars under changing climatic conditions. In millet improvement, an in-depth account of NGS, integrating genomics data with different biotechnology tools, is reviewed in this context.

Halophytes as new model plant species for salt tolerance strategies

Soil salinity is becoming a growing issue nowadays, severely affecting the world's most productive agricultural landscapes. With intersecting and competitive challenges of shrinking agricultural lands and increasing demand for food, there is an emerging need to build resilience for adaptation to anticipated climate change and land degradation. This necessitates the deep decoding of a gene pool of crop plant wild relatives which can be accomplished through salt-tolerant species, such as halophytes, in order to reveal the underlying regulatory mechanisms. Halophytes are generally defined as plants able to survive and complete their life cycle in highly saline environments of at least 200-500 mM of salt solution. The primary criterion for identifying salt-tolerant grasses (STGs) includes the presence of salt glands on the leaf surface and the Na⁺ exclusion mechanism since the interaction and replacement of Na⁺ and K⁺ greatly determines the survivability of STGs in saline environments. During the last decades or so, various salt-tolerant grasses/halophytes have been explored for the mining of salt-tolerant genes and testing their efficacy to improve the limit of salt tolerance in crop plants. Still, the utility of halophytes is limited due to the non-availability of any model halophytic plant system as well as the lack of complete genomic information. To date, although Arabidopsis (Arabidopsis thaliana) and salt cress (Thellungiella halophila) are being used as model plants in most salt tolerance studies, these plants are short-lived and can tolerate salinity for a shorter duration only. Thus, identifying the unique genes for salt tolerance pathways in halophytes and their introgression in a related cereal genome for better tolerance to salinity is the need of the hour. Modern technologies including RNA sequencing and genome-wide mapping along with advanced bioinformatics programs have advanced the decoding of the whole genetic information of plants and the development of probable algorithms to correlate stress tolerance limit and yield potential. Hence, this article has been compiled to explore the naturally occurring halophytes as potential model plant species for abiotic stress tolerance and to further breed crop plants to enhance salt tolerance through genomic and molecular tools.

Genetic enhancement of climate-resilient traits in small millets: A review

Agriculture is facing the challenge of feeding the ever-growing population that is projected to reach ten billion by 2050. While improving crop yield and productivity can address this challenge, the increasing effects of global warming and climate change seriously threaten agricultural productivity. Thus, genomics and genome modification technologies are crucial to improving climate-resilient traits to enable sustained yield and productivity; however, significant research focuses on staple crops such as rice, wheat, and maize. Crops that are naturally climate-resilient and nutritionally superior to staple cereals, such as small millets, remain neglected and underutilized by mainstream research. The ability of small millets to grow in marginal regions having limited irrigation and poor soil fertility makes these crops a better choice for cultivation in arid and semi-arid areas. Hence, mainstreaming small millets for cultivation and using omics technologies to dissect the climate-resilient traits to identify the molecular determinants underlying these traits are imperative for addressing food and nutritional security. In this context, the review discusses the genomics and genome modification approaches for dissecting key traits in small millets and their application for improving these traits in cultivated germplasm. The review also discusses biofortification for nutritional security and machine-learning approaches for trait improvement in small millets. Altogether, the review provides a roadmap for the effective use of next-generation approaches for trait improvement in small millets. This will lead to the development of improved varieties for addressing multiple insecurities prevailing in the present climate change scenario.

Salinity tolerance mechanisms and their breeding implications

BACKGROUND

The era of first green revolution brought about by the application of chemical fertilizers surely led to the explosion of food grains, but left behind the notable problem of salinity. Continuous application of these fertilizers coupled with fertilizer-responsive crops make the country self-reliant, but continuous deposition of these led to altered the water potential and thus negatively affecting the proper plant functioning from germination to seed setting.

MAIN BODY

Increased concentration of anion and cations and their accumulation and distribution cause cellular toxicity and ionic imbalance. Plants respond to salinity stress by any one of two mechanisms, viz., escape or tolerate, by either limiting their entry via root system or controlling their distribution and storage. However, the understanding of tolerance mechanism at the physiological, biochemical, and molecular levels will provide an insight for the identification of related genes and their introgression to make the crop more resilient against salinity stress.

SHORT CONCLUSION

Novel emerging approaches of plant breeding and biotechnologies such as genome-wide association studies, mutational breeding, marker-assisted breeding, double haploid production, hyperspectral imaging, and CRISPR/Cas serve as engineering tools for dissecting the in-depth physiological mechanisms. These techniques have well-established implications to understand plants' adaptions to develop more tolerant varieties and lower the energy expenditure in response to stress and, constitutively fulfill the void that would have led to growth resistance and yield penalty.

A Review of Recent Advances and Future Directions in the Management of Salinity Stress in Finger Millet

Salinity stress is a major environmental impediment affecting the growth and production of crops. Finger millet is an important cereal grown in many arid and semi-arid areas of the world characterized by erratic rainfall and scarcity of good-quality water. Finger millet salinity stress is caused by the accumulation of soluble salts due to irrigation without a proper drainage system, coupled with the underlying rocks having a high salt content, which leads to the salinization of arable land. This problem is projected to be exacerbated by climate change. The use of new and efficient strategies that provide stable salinity tolerance across a wide range of environments can guarantee sustainable production of finger millet in the future. In this review, we analyze the strategies that have been used for salinity stress management in finger millet production and discuss potential future directions toward the development of salt-tolerant finger millet varieties. This review also describes how advanced biotechnological tools are being used to develop salt-tolerant plants. The biotechnological techniques discussed in this review are simple to implement, have design flexibility, low cost, and highly efficient. This information provides insights into enhancing finger millet salinity tolerance and improving production.

Genetic and genomic resources, and breeding for accelerating improvement of small millets: current status and future interventions

Current agricultural and food systems encourage research and development on major crops, neglecting regionally important minor crops. Small millets include a group of small- seeded cereal crops of the grass family Poaceae. This includes finger millet, foxtail millet, proso millet, barnyard millet, kodo millet, little millet, teff, fonio, job’s tears, guinea millet, and browntop millet. Small millets are an excellent choice to supplement major staple foods for crop and dietary diversity because of their diverse adaptation on marginal lands, less water requirement, lesser susceptibility to stresses, and nutritional superiority compared to major cereal staples. Growing interest among consumers about healthy diets together with climate-resilient features of small millets underline the necessity of directing more research and development towards these crops. Except for finger millet and foxtail millet, and to some extent proso millet and teff, other small millets have received minimal research attention in terms of development of genetic and genomic resources and breeding for yield enhancement. Considerable breeding efforts were made in finger millet and foxtail millet in India and China, respectively, proso millet in the United States of America, and teff in Ethiopia. So far, five genomes, namely foxtail millet, finger millet, proso millet, teff, and Japanese barnyard millet, have been sequenced, and genome of foxtail millet is the smallest (423-510 Mb) while the largest one is finger millet (1.5 Gb). Recent advances in phenotyping and genomics technologies, together with available germplasm diversity, could be utilized in small millets improvement. This review provides a comprehensive insight into the importance of small millets, the global status of their germplasm, diversity, promising germplasm resources, and breeding approaches (conventional and genomic approaches) to accelerate climate-resilient and nutrient-dense small millets for sustainable agriculture, environment, and healthy food systems.

Phenomics and genomics of finger millet: current status and future prospects

Diverse gene pool, advanced plant phenomics and genomics methods enhanced genetic gain and understanding of important agronomic, adaptation and nutritional traits in finger millet. Finger millet (Eleusine coracana L. Gaertn) is an important minor millet for food and nutritional security in semi-arid regions of the world. The crop has wide adaptability and can be grown right from high hills in Himalayan region to coastal plains. It provides food grain as well as palatable straw for cattle, and is fairly climate resilient. The crop has large gene pool with distinct features of both Indian and African germplasm types. Interspecific hybridization between Indian and African germplasm has resulted in greater yield enhancement and disease resistance. The crop has shown numerous advantages over major cereals in terms of stress adaptation, nutritional quality and health benefits. It has indispensable repository of novel genes for the benefits of mankind. Although rapid strides have been made in allele mining in model crops and major cereals, the progress in finger millet genomics is lacking. Comparative genomics have paved the way for the marker-assisted selection, where resistance gene homologues of rice for blast and sequence variants for nutritional traits from other cereals have been invariably used. Transcriptomics studies have provided preliminary understanding of the nutritional variation, drought and salinity tolerance. However, the genetics of many important traits in finger millet is poorly understood and need systematic efforts from biologists across disciplines. Recently, deciphered finger millet genome will enable identification of candidate genes for agronomically and nutritionally important traits. Further, improvement in genome assembly and application of genomic selection as well as genome editing in near future will provide plethora of information and opportunity to understand the genetics of complex traits.

Finger Millet [Eleusine coracana (L.) Gaertn.] Improvement: Current Status and Future Interventions of Whole Genome Sequence

The whole genome sequence (WGS) of the much awaited, nutrient rich and climate resilient crop, finger millet (Eleusine coracana (L.) Gaertn.) has been released recently. While possessing superior mineral nutrients and excellent shelf life as compared to other major cereals, multiploidy nature of the genome and relatively small plantation acreage in less developed countries hampered the genome sequencing of finger millet, disposing it as one of the lastly sequenced genomes in cereals. The genomic information available for this crop is very little when compared to other major cereals like rice, maize and barley. As a result, only a limited number of genetic and genomic studies has been undertaken for the improvement of this crop. Finger millet is known especially for its superior calcium content, but the high-throughput studies are yet to be performed to understand the mechanisms behind calcium transport and grain filling. The WGS of finger millet is expected to help to understand this and other important molecular mechanisms in finger millet, which may be harnessed for the nutrient fortification of other cereals. In this review, we discuss various efforts made so far on the improvement of finger millet including genetic improvement, transcriptome analysis, mapping of quantitative trait loci (QTLs) for traits, etc. We also discuss the pitfalls of modern genetic studies and provide insights for accelerating the finger millet improvement with the interventions of WGS in near future. Advanced genetic and genomic studies aided by WGS may help to improve the finger millet, which will be helpful to strengthen the nutritional security in addition to food security in the developing countries of Asia and Africa.

PCA22 acts as a suppressor of atrzf1 to mediate proline accumulation in response to abiotic stress in Arabidopsis

Proline metabolism is important for environmental responses, plant growth, and development. However, its precise roles in plant abiotic stress tolerance are not well understood. Mutants are valuable for the identification of new genes and for elucidating their roles in physiological mechanisms. We applied a suppressor mutation approach to identify novel genes involved in the regulation of proline metabolism in Arabidopsis. Using the atrzf1 (Arabidopsis thaliana ring zinc finger 1) mutant as a parental line for activation tagging mutagenesis, we selected several mutants with suppressed induction of proline accumulation under dehydration conditions. One of the selected mutants [proline content alterative 22 (pca22)] appeared to have reduced proline contents compared with the atrzf1 mutant under drought stress. Generally, pca22 mutant plants displayed suppressed atrzf1 insensitivity to dehydration and abscisic acid during early seedling growth. Additionally, the pca22 mutant exhibited shorter pollen tube length than wild-type (WT) and atrzf1 plants. Furthermore, PCA22-overexpressing plants were more sensitive to dehydration stress than the WT and RNAi lines. Green fluorescent protein-tagged PCA22 was localized to the cytoplasm of transgenic Arabidopsis cells. Collectively, these results suggest that pca22 acts as dominant suppressor mutant of atrzf1 in the abiotic stress response.

Gene Discovery and Advances in Finger Millet [Eleusine coracana (L.) Gaertn.] Genomics-An Important Nutri-Cereal of Future

The rapid strides in molecular marker technologies followed by genomics, and next generation sequencing advancements in three major crops (rice, maize and wheat) of the world have given opportunities for their use in the orphan, but highly valuable future crops, including finger millet [Eleusine coracana (L.) Gaertn.]. Finger millet has many special agronomic and nutritional characteristics, which make it an indispensable crop in arid, semi-arid, hilly and tribal areas of India and Africa. The crop has proven its adaptability in harsh conditions and has shown resilience to climate change. The adaptability traits of finger millet have shown the advantage over major cereal grains under stress conditions, revealing it as a storehouse of important genomic resources for crop improvement. Although new technologies for genomic studies are now available, progress in identifying and tapping these important alleles or genes is lacking. RAPDs were the default choice for genetic diversity studies in the crop until the last decade, but the subsequent development of SSRs and comparative genomics paved the way for the marker assisted selection in finger millet. Resistance gene homologs from NBS-LRR region of finger millet for blast and sequence variants for nutritional traits from other cereals have been developed and used invariably. Population structure analysis studies exhibit 2-4 sub-populations in the finger millet gene pool with separate grouping of Indian and exotic genotypes. Recently, the omics technologies have been efficiently applied to understand the nutritional variation, drought tolerance and gene mining. Progress has also occurred with respect to transgenics development. This review presents the current biotechnological advancements along with research gaps and future perspective of genomic research in finger millet.

Salt tolerance mechanisms in Salt Tolerant Grasses (STGs) and their prospects in cereal crop improvement

Increasing soil salinity in the agricultural fields all over the world is a matter of concern. Salinity poses a serious threat to the normal growth and development of crop plants. What adds to the concern is that all the cereal crops are sensitive to increasing soil salinity. So it is implacable to either search for salinity resistant varieties of crop plants or transform them genetically to sustain growth and reproducibility at increasing salinity stress. For the second perspective, mining the salt tolerant genes in the close relatives of cereal crops apparently becomes important, and most specifically in the salt tolerant grasses (STGs). STGs include the halophytes, facultative halophytes and salt-tolerant glycophytes of the family Poaceae. In this review the potentiality of STGs has been evaluated for increasing the salinity tolerance of cereal crops. STGs are capable of surviving at increasing salt stress by utilizing different mechanisms that include vacuolization of toxic Na+ and Cl- in mature or senescing leaves, secretion of excess salts by salt glands, accumulation of osmolytes like proline and glycine betaine, and scavenging of ROS by antioxidative enzymes. The STGs are a therefore a potent source of salt tolerant genes.

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.

An Effective Procedure for In Vitro Culture of Eleusine coracana (L.) and Its Application

Efficient protocols for callus production, plantlet regeneration, protoplast isolation, and micronucleation of finger millet (Eleusine coracana (L.) Gaertn.) were developed. White nodulated calli were formed on medium with N6 macrosalts, MS microsalts, 2.4-dichlorophenoxyacetic acid (2 mg L−1), kinetin (0.4 mg L−1), 1-naphthalene acetic acid (2 mg L−1), and certain additives. It was found that appropriate supplementation leads to formation of numerous shoots. Healthy rooted plantlets formed on hormone-free media. Although different tested additives had no significant effect on percentage of callus formation, it affected callus quality that further dictated plant-forming capacities. Seedlings were better source tissues for protoplasts isolation compared to callus cultures. About protoplasts were isolated from one gram of seedling coleoptyles. Microcolonies were visible after 20–25 days' incubation on KM8p medium supplemented with glutamine (100 mg L−1) and proline (500 mg L−1). Here we also present a procedure of an efficient induction of micronuclei after chlorpropham (10 μM) and cytochalasin-B (20 μM) seedlings treatment with subsequent microprotoplasts isolation. This technique is discussed for the transfer of alien chromosomes and genes from finger millet by microprotoplast-mediated chromosome transfer.

Overexpression of a heat shock protein (ThHSP18.3) from Tamarix hispida confers stress tolerance to yeast

It is well known that plant heat shock proteins (HSPs) play important roles both in response to adverse environmental conditions and in various developmental processes. However, among plant HSPs, the functions of tree plant HSPs are poorly characterized. To improve our understanding of tree HSPs, we cloned and characterized an HSP gene (ThHSP18.3) from Tamarix hispida. Sequence alignment reveals that ThHSP18.3 belongs to the class I small heat shock protein family. A transient expression assay showed that ThHSP18.3 protein was targeted to the cell nucleus. Treatment of Tamarix hispida with cold and heat shock highly induced ThHSP18.3 expression in all studied leaves, roots and stems, whereas, treatment of T. hispida with NaCl, NaHCO(3), and PEG induced ThHSP18.3 expression in leaves and decreased its expression in roots and stems. Further, to study the role of ThHSP18.3 in stress tolerance under different stress conditions, we cloned ThHSP18.3 into the pYES2 vector, transformed and expressed the vector in yeast Saccharomyces cerevisiae. Yeast cells transformed with an empty pYES2 vector were employed as a control. Compared to the control, yeast cells expressing ThHSP18.3 showed greater tolerance to salt, drought, heavy metals, and both low and high temperatures, indicating that ThHSP18.3 confers tolerance to these stress conditions. These results suggested that ThHSP18.3 is involved in tolerance to a variety of stress conditions in T. hispida.

Isolation and characterization of a pigeonpea cyclophilin (CcCYP) gene, and its over-expression in Arabidopsis confers multiple abiotic stress tolerance

A full-length cDNA clone of pigeonpea (Cajanus cajan L.) encoding cyclophilin (CcCYP) has been isolated from the cDNA library of plants subjected to drought stress. Amino acid sequence of CcCYP disclosed similarity with that of single-domain cytosolic cyclophilins of various organisms. Expression profile of CcCYP in pigeonpea plants is strongly induced by different abiotic stresses, indicating its stress-responsive nature. Compared to the control plants, the transgenic Arabidopsis lines expressing CcCYP exhibited high-level tolerance against major abiotic stresses, viz., drought, salinity and extreme temperatures as evidenced by increased plant survival, biomass, chlorophyll content and profuse root growth. The CcCYP transgenics, compared to the controls, revealed enhanced peptidyl-propyl cis-trans isomerase (PPIase) activity under stressed conditions, owing to transcriptional activation of stress-related genes besides intrinsic chaperonic activity of the cyclophilin. The transgenic plants subjected to salt stress exhibited higher Na(+) ion accumulation in roots as compared to shoots, while a reverse trend was observed in the salt-stressed control plants, implicating the involvement of CcCYP in the maintenance of ion homeostasis. Expression pattern of CcCYP:GFP fusion protein confirmed the localization of CcCYP predominantly in the nucleus as revealed by intense green fluorescence. The overall results amply demonstrate the implicit role of CcCYP in conferring multiple abiotic stress tolerance at whole-plant level.

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.

Expression of pigeonpea hybrid-proline-rich protein encoding gene (CcHyPRP) in yeast and Arabidopsis affords multiple abiotic stress tolerance

A hybrid-proline-rich protein encoding gene (CcHyPRP) has been isolated and characterized, for the first time, from the subtracted cDNA library of pigeonpea (Cajanus cajan L.) plants subjected to drought stress. Functionality of CcHyPRP has been validated for abiotic stress tolerance using the heterologous yeast and Arabidopsis systems. The CcHyPRP contained a repetitive proline-rich (PR) N-terminal domain and a conserved eight cysteine motif (8CM) at the C-terminus. Southern analysis disclosed single-copy nature of CcHyPRP gene in the pigeonpea genome. Northern analysis revealed higher levels of CcHyPRP transcripts in PEG, NaCl, heat (42 degrees C), cold and ABA-treated plants compared with the weak signals observed in the untreated plants, suggesting stress-responsive nature of the CcHyPRP gene. In yeast, expression of CcHyPRP imparted marked tolerance against abiotic stresses exerted by PEG, high temperature, NaCl and LiCl. Transgenic Arabidopsis lines, expressing CcHyPRP under the control of CaMV35S and rd29A promoters, when subjected to PEG, mannitol, NaCl, LiCl and heat (42 degrees C) stress, developed into healthy plants with profuse root system and increased biomass in contrast to the weak-stunted wild-type plants. The CcHyPRP-transgenics driven by stress-inducible rd29A exhibited similar stress-tolerance as that of CaMV35S-lines without any negative effects on plant morphology, implying that stress-inducible promoters are preferable for production of stress tolerant transgenics. The overall results amply demonstrate the profound effect of CcHyPRP in bestowing multiple abiotic stress tolerance at cellular and whole plant levels. Accordingly, the multipotent CcHyPRP seems promising as a prime candidate gene to fortify crop plants with abiotic stress tolerance.

Transcriptome map for seedling stage specific salinity stress response indicates a specific set of genes as candidate for saline tolerance in Oryza sativa L

Oryza sativa L. cv IR64 is a widely cultivated, salt-sensitive indica rice, while Pokkali is a well-known, naturally salt-tolerant relative. To understand the molecular basis of differences in their salinity tolerance, three subtractive cDNA libraries were constructed. A total of 1,194 salinity-regulated cDNAs are reported here that may serve as repositories for future individual gene-based functional genomics studies. Gene expression data using macroarrays and Northern blots gives support to our hypothesis that salinity tolerance of Pokkali may be due to constitutive overexpression of many genes that function in salinity tolerance and are stress inducible in IR64. Analysis of genome architecture revealed the presence of these genes on all the chromosomes with several distinct clusters. Notably, a few mapped on one of the major quantitative trait loci - Saltol - on chromosome 1 and were found to be differentially regulated in the two contrasting genotypes. The present study also defines a set of known abiotic stress inducible genes, including CaMBP, GST, LEA, V-ATPase, OSAP1 zinc finger protein, and transcription factor HBP1B, that were expressed at high levels in Pokkali even in the absence of stress. These proposed genes may prove useful as "candidates" in improving salinity tolerance in crop plants using transgenic approach.

A heat shock protein gene (hsp22.4) from Chaetomium globosum confers heat and Na2CO3 tolerance to yeast

A small heat shock protein gene (hsp22.4) was cloned from Chaetomium globosum using rapid amplification of cDNA ends (RACE). The 986-bp full-length hsp22.4 cDNA contains a 609-bp open reading frame encoding a 202-amino-acid protein with an estimated molecular mass of 22.4 kDa. The hsp22.4 gene was amplified using specific primers in the 5' and 3' untranslated regions of the hsp22.4 cDNA. The temporal expression of hsp22.4 was measured in C. globosum by real-time reverse transcriptase-polymerase chain reaction after exposure to heat, cold, Na(2)CO(3), and NaCl. The expression of hsp22.4 was induced by heat and Na(2)CO(3) treatment and inhibited by cold and NaCl treatment. The hsp22.4 gene was inserted into pYES2 containing the inducible GAL1 promoter and transferred into yeast (Saccharomyces cerevisiae) for expression. The hsp22.4 transgenic yeast displayed significantly greater resistance to heat and Na(2)CO(3) stresses than control (yeast cells transformed with empty pYES2), suggesting that the expression of hsp22.4 gene confers not only heat tolerance but also significant alkali (Na(2)CO(3)) stress tolerance.

Emerging trends in the functional genomics of the abiotic stress response in crop plants

Plants are exposed to different abiotic stresses, such as water deficit, high temperature, salinity, cold, heavy metals and mechanical wounding, under field conditions. It is estimated that such stress conditions can potentially reduce the yield of crop plants by more than 50%. Investigations of the physiological, biochemical and molecular aspects of stress tolerance have been conducted to unravel the intrinsic mechanisms developed during evolution to mitigate against stress by plants. Before the advent of the genomics era, researchers primarily used a gene-by-gene approach to decipher the function of the genes involved in the abiotic stress response. However, abiotic stress tolerance is a complex trait and, although large numbers of genes have been identified to be involved in the abiotic stress response, there remain large gaps in our understanding of the trait. The availability of the genome sequences of certain important plant species has enabled the use of strategies, such as genome-wide expression profiling, to identify the genes associated with the stress response, followed by the verification of gene function by the analysis of mutants and transgenics. Certain components of both abscisic acid-dependent and -independent cascades involved in the stress response have already been identified. Information originating from the genome-wide analysis of abiotic stress tolerance will help to provide an insight into the stress-responsive network(s), and may allow the modification of this network to reduce the loss caused by stress and to increase agricultural productivity.