Transcriptomic and metabolic responses of Calotropis procera to salt and drought stress

Combined transcriptomics and metabolomics analysis reveals salinity stress specific signaling and tolerance responses in the seagrass Zostera japonica

KEY MESSAGE

Multiple regulatory pathways of Zostera japonica to salt stress were identified through growth, physiological, transcriptomic and metabolomic analyses. Seagrasses are marine higher submerged plants that evolved from terrestrial monocotyledons and have fully adapted to the high saline seawater environment during the long evolutionary process. As one of the seagrasses growing in the intertidal zone, Zostera japonica not only has the ability to quickly adapt to short-term salt stress but can also survive at salinities ranging from the lower salinity of the Yellow River estuary to the higher salinity of the bay, making it a good natural model for studying the mechanism underlying the adaptation of plants to salt stress. In this work, we screened the growth, physiological, metabolomic, and transcriptomic changes of Z. japonica after a 5-day exposure to different salinities. We found that high salinity treatment impeded the growth of Z. japonica, hindered its photosynthesis, and elicited oxidative damage, while Z. japonica increased antioxidant enzyme activity. At the transcriptomic level, hypersaline stress greatly reduced the expression levels of photosynthesis-related genes while increasing the expression of genes associated with flavonoid biosynthesis. Meanwhile, the expression of candidate genes involved in ion transport and cell wall remodeling was dramatically changed under hypersaline stress. Moreover, transcription factors signaling pathways such as mitogen-activated protein kinase (MAPK) were also significantly influenced by salt stress. At the metabolomic level, Z. japonica displayed an accumulation of osmolytes and TCA mediators under hypersaline stress. In conclusion, our results revealed a complex regulatory mechanism in Z. japonica under salt stress, and the findings will provide important guidance for improving salt resistance in crops.

Transcriptome Analysis and Metabolic Profiling Reveal the Key Regulatory Pathways in Drought Stress Responses and Recovery in Tomatoes

Drought stress is a major abiotic factor affecting tomato production and fruit quality. However, the genes and metabolites associated with tomato responses to water deficiency and rehydration are poorly characterized. To identify the functional genes and key metabolic pathways underlying tomato responses to drought stress and recovery, drought-susceptible and drought-tolerant inbred lines underwent transcriptomic and metabolomic analyses. A total of 332 drought-responsive and 491 rehydration-responsive core genes were robustly differentially expressed in both genotypes. The drought-responsive and rehydration-responsive genes were mainly related to photosynthesis-antenna proteins, nitrogen metabolism, plant-pathogen interactions, and the MAPK signaling pathway. Various transcription factors, including homeobox-leucine zipper protein ATHB-12, NAC transcription factor 29, and heat stress transcription factor A-6b-like, may be vital for tomato responses to water status. Moreover, 24,30-dihydroxy-12(13)-enolupinol, caffeoyl hawthorn acid, adenosine 5'-monophosphate, and guanosine were the key metabolites identified in both genotypes under drought and recovery conditions. The combined transcriptomic and metabolomic analysis highlighted the importance of 38 genes involved in metabolic pathways, the biosynthesis of secondary metabolites, the biosynthesis of amino acids, and ABC transporters for tomato responses to water stress. Our results provide valuable clues regarding the molecular basis of drought tolerance and rehydration. The data presented herein may be relevant for genetically improving tomatoes to enhance drought tolerance.

Feeding-induced plant metabolite responses to a phoretic gall mite, its carrier psyllid and both, after detachment

Phoresy is one of the most distinctive relationships between mites and insects, and the off-host interaction between phoretic mites and their carriers is the most critical factor sustaining the phoretic association. As phoretic associations commonly occur in temporary habitats, little is known about off-host interactions between phoronts and carriers. However, an off-host interaction has been reported, in which the plant-mediated competition between a phoretic gall mite, Aceria pallida, and its psyllid vector, Bactericera gobica, after detachment decreases leaf abscission caused by B. gobica and then directly facilitates their phoretic association. In this obligate phoresy, A. pallida seasonally attaches to B. gobica for overwinter survival and they share the same host plant, Lycium barbarum, during the growing season. It is unknown how the host plant responds to these two herbivores and what plant metabolites are involved in their interspecific interaction. Here, effects of A. pallida and B. gobica on the host plant's transcriptome and metabolome, and on enzymes involved in plant defence, at various infestation stages were studied by inoculating A. pallida and B. gobica either separately or simultaneously on leaves of L. barbarum. Our results showed that (a) A. pallida significantly promoted primary and secondary metabolite accumulation, (b) B. gobica markedly inhibited primary and secondary metabolite accumulation and had little influence on defence enzyme activity, and (c) under simultaneous A. pallida and B. gobica infestation, an intermediate response was predicted. These findings indicate that A. pallida and B. gobica have different effects on host plants, A. pallida inhibits B. gobica mainly by increasing the secondary metabolism of L. barbarum, whereas B. gobica inhibits A. pallida mainly by decreasing the primary metabolism of L. barbarum. In conjunction with our previous research, we speculate that this trade-off in host plant metabolite response between A. pallida and B. gobica after detachment promotes a stable phoretic association.

Lipid Metabolomic and Transcriptomic Analyses Reveal That Phosphatidylcholine Enhanced the Resistance of Peach Seedlings to Salt Stress through Phosphatidic Acid

Soil salinity is a major conlinet limiting sustainable agricultural development in peach tree industry. In this study, lipid metabolomic pathway analysis indicated that phosphatidic acid is essential for root resistance to salt stress in peach seedlings. Through functional annotation analysis of differentially expressed genes in transcriptomics, we found that MAPK signaling pathway is closely related to peach tree resistance to salt stress, wherein PpMPK6 expression is significantly upregulated. Under salt conditions, the OE-PpMPK6 Arabidopsis thaliana (L.) Heynh. line showed higher resistance to salt stress than WT and KO-AtMPK6 lines. Furthermore, we found that the Na⁺ content in OE-PpMPK6 roots was significantly lower than that in WT and KO-AtMPK6 roots, indicating that phosphatidic acid combined with PpMPK6 activated the SOS1 (salt-overly-sensitive 1) protein to enhance Na⁺ efflux, thus alleviating the damage caused by NaCl in roots; these findings provide insight into the salt stress-associated transcriptional regulation.

Integrated metabolome, transcriptome analysis, and multi-flux full-length sequencing offer novel insights into the function of lignin biosynthesis as a Sesuvium portulacastrum response to salt stress

Sesuvium portulacastrum is a typical halophyte. However, few studies have investigated its salt-tolerant molecular mechanism. In this study, metabolome, transcriptome, and multi-flux full-length sequencing analysis were conducted to investigate the significantly different metabolites (SDMs) and differentially expressed genes (DEGs) of S. portulacastrum samples under salinity. The complete-length transcriptome of S. portulacastrum was developed, which contained 39,659 non-redundant unigenes. RNA-seq results showed that 52 DEGs involved in lignin biosynthesis may be responsible for S. portulacastrum salt tolerance. Furthermore, 130 SDMs were identified, and the salt response could be attributed to the p-coumaryl alcohol-rich in lignin biosynthesis. The co-expression network that was constructed after comparing the different salt treatment processes showed that the p-Coumaryl alcohol was linked to 30 DEGs. Herein, 8 structures genes, i.e., Sp4CL, SpCAD, SpCCR, SpCOMT, SpF5H, SpCYP73A, SpCCoAOMT, and SpC3'H were identified as significant factors in regulating lignin biosynthesis. Further investigation revealed that 64 putative transcription factors (TFs) may interact with the promoters of the above-mentioned genes. Together, the data revealed a potential regulatory network comprising important genes, putative TFs, and metabolites involved in the lignin biosynthesis of S. portulacastrum roots under salt stress, which could serve as a rich useful genetic resource for breeding excellent salt-tolerant plants.

Transcriptomic and Metabolomic Analyses Reveal That Fullerol Improves Drought Tolerance in Brassica napus L

Carbon nanoparticles have potential threats to plant growth and stress tolerance. The polyhydroxy fullerene-fullerol (one of the carbon nanoparticles) could increase biomass accumulation in several plants subjected to drought; however, the underlying molecular and metabolic mechanisms governed by fullerol in improving drought tolerance in Brassica napus remain unclear. In the present study, exogenous fullerol was applied to the leaves of B. napus seedlings under drought conditions. The results of transcriptomic and metabolomic analyses revealed changes in the molecular and metabolic profiles of B. napus. The differentially expressed genes and the differentially accumulated metabolites, induced by drought or fullerol treatment, were mainly enriched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to carbohydrate metabolism (e.g., "carbon metabolism" and "galactose metabolism"), amino acid metabolism (e.g., "biosynthesis of amino acids" and "arginine and proline metabolism"), and secondary metabolite metabolism (e.g., "biosynthesis of secondary metabolites"). For carbohydrate metabolism, the accumulation of oligosaccharides (e.g., sucrose) was decreased, whereas that of monosaccharides (e.g., mannose and myo-inositol) was increased by drought. With regard to amino acid metabolism, under drought stress, the accumulation of amino acids such as phenylalanine and tryptophan decreased, whereas that of glutamate and proline increased. Further, for secondary metabolite metabolism, B. napus subjected to soil drying showed a reduction in phenolics and flavonoids, such as hyperoside and trans-3-coumaric acid. However, the accumulation of carbohydrates was almost unchanged in fullerol-treated B. napus subjected to drought. When exposed to water shortage, the accumulation of amino acids, such as proline, was decreased upon fullerol treatment. However, that of phenolics and flavonoids, such as luteolin and trans-3-coumaric acid, was enhanced. Our findings suggest that fullerol can alleviate the inhibitory effects of drought on phenolics and flavonoids to enhance drought tolerance in B. napus.

Metabolic and Physiological Changes in the Roots of Two Oat Cultivars in Response to Complex Saline-Alkali Stress

Saline-alkali stress is a major abiotic stress factor in agricultural productivity. Oat (Avena sativa L.) is a saline-alkali tolerant crop species. However, molecular mechanisms of saline-alkali tolerance in oats remain unclear. To understand the physiological and molecular mechanisms underlying seedling saline-alkali tolerance in oats, the phenotypic and metabolic responses of two oat cultivars, Baiyan7 (BY, tolerant cultivar) and Yizhangyan4 (YZY, sensitive cultivar), were characterized under saline-alkali stress conditions. Compared with YZY, BY showed better adaptability to saline-alkali stress. A total of 151 and 96 differential metabolites induced by saline-alkali stress were identified in roots of BY and YZY, respectively. More detailed analyses indicated that enhancements of energy metabolism and accumulations of organic acids were the active strategies of oat roots, in response to complex saline-alkali stress. The BY utilized sugars via sugar consumption more effectively, while amino acids strengthened metabolism and upregulated lignin and might be the positive responses of BY roots to saline-alkali stress, which led to a higher osmotic adjustment of solute concentrations and cell growth. The YZY mainly used soluble sugars and flavonoids combined with sugars to form glycosides, as osmotic regulatory substances or antioxidant substances, to cope with saline-alkali stress. The analyses of different metabolites of roots of tolerant and sensitive cultivars provided an important theoretical basis for understanding the mechanisms of saline-alkali tolerance and increased our knowledge of plant metabolism regulation under stress. Meanwhile, some related metabolites, such as proline, betaine, and p-coumaryl alcohol, can also be used as candidates for screening saline-alkali tolerant oat cultivars.

Comparative Transcriptomics Analysis of Roots and Leaves under Cd Stress in Calotropis gigantea L

Calotropis gigantea is often found in mining areas with heavy metal pollution. However, little is known about the physiological and molecular response mechanism of C. gigantea to Cd stress. In the present study, Cd tolerance characteristic of C. gigantea and the potential mechanisms were explored. Seed germination test results showed that C. gigantea had a certain Cd tolerance capacity. Biochemical and transcriptomic analysis indicated that the roots and leaves of C. gigantea had different responses to early Cd stress. A total of 176 and 1618 DEGs were identified in the roots and leaves of C. gigantea treated with Cd compared to the control samples, respectively. Results indicated that oxidative stress was mainly initiated in the roots of C. gigantea, whereas the leaves activated several Cd detoxification processes to cope with Cd, including the upregulation of genes involved in Cd transport (i.e., absorption, efflux, or compartmentalization), cell wall remodeling, antioxidant system, and chelation. This study provides preliminary information to understand how C. gigantea respond to Cd stress, which is useful for evaluating the potential of C. gigantea in the remediation of Cd-contaminated soils.

Integrated transcriptomics and metabolomics analysis to characterize alkali stress responses in canola (Brassica napus L.)

BACKGROUND

Soil salinization is a major constraint limiting agricultural development and affecting crop growth and productivity, especially in arid and semi-arid regions. Understanding the molecular mechanism of the adaptability of canola to salt stress is very important to improve the salt tolerance of canola and promote its cultivation in saline alkali soil.

RESULTS

To identify the metabolomic and transcriptomic mechanisms of canola under alkaline salt stress, we collected roots of control (no salt treatment) and 72 h Na₂CO₃-stressed canola seedlings (hydroponics) for metabolic profiling of metabolites, supplemented with RNA-Seq analysis and real-time quantitative PCR validation. Metabolomic analysis showed that the metabolites of amino acids and fatty acids were higher accumulated under alkaline salt stress, including L-proline, L-glutamate, L-histidine, L-phenylalanine, L-citrulline, L-tyrosine, L-saccharopine, L-tryptophan, linoleic acid, dihomo gamma linolenic acid, alpha linolenic acid, Eric acid, oleic acid and neuronic acid, while the metabolism of carbohydrate (sucrase, alpha, alpha trehalose), polyol (ribitol), UDP-D-galactose, D-mannose, D-fructose and D-glucose 6-phosphate decreased. Transcriptomic and metabolomic pathway analysis indicated that carbohydrate metabolism may not play an important role in the resistance of canola to alkaline salt stress. Organic acid metabolism (fatty acid accumulation) and amino acid metabolism are important metabolic pathways in the root of canola under alkaline salt stress.

CONCLUSIONS

These results suggest that the genes and metabolites involved in fatty acid metabolism and amino acids metabolism in roots of canola may regulate salt tolerance of canola seedlings under alkaline salt stress, which improves our understanding of the molecular mechanisms of salt tolerance in canola.

Transcriptomics and Metabolomics Reveal Purine and Phenylpropanoid Metabolism Response to Drought Stress in Dendrobium sinense, an Endemic Orchid Species in Hainan Island

Drought stress is a bottleneck factor for plant growth and development, especially in epiphytic orchids that absorb moisture mainly from the air. Recent studies have suggested that there are complex transcriptional regulatory networks related to drought stress in Dendrobium sinense. In this study, the transcription and metabolite alterations involved in drought stress response in D. sinense were investigated through RNA-seq and metabolomics. A total of 856 metabolites were identified from stressed and control samples, with 391 metabolites showing significant differences. With PacBio and Illumina RNA sequencing, 72,969 genes were obtained with a mean length of 2,486 bp, and 622 differentially expressed genes (DEGs) were identified. Correlation analysis showed 7 differential genes, and 39 differential metabolites were involved in interaction networks. The network analysis of differential genes and metabolites suggested that the pathways of purine metabolism and phenylpropanoid biosynthesis may play an important role in drought response in D. sinense. These results provide new insights and reference data for culturally important medicinal plants and the protection of endangered orchids.

Salt tolerance of Calotropis procera begins with immediate regulation of aquaporin activity in the root system

The ability to respond quickly to salt stress can determine the tolerance level of a species. Here, we test how rapidly the roots of Calotropis procera react to high salinity conditions. In the first 24 h after saline exposure, the plants reduced stomatal conductance, increased CO₂ assimilation, and water use efficiency. Thus, the root tissue showed an immediate increase in soluble sugars, free amino acid, and soluble protein contents. Twelve aquaporins showed differential gene expression in the roots of C. procera under salinity. Transcriptional upregulation was observed only after 2 h, with greater induction of CpTIP1.4 (fourfold). Transcriptional downregulation, in turn, occurred mainly after 8 h, with the largest associated with CpPIP1.2 (fourfold). C. procera plants responded quickly to high saline levels. Our results showed a strong stomatal control associated with high free amino acid and soluble sugar contents, regulated aquaporin expression in roots, and supported the high performance of the root system of C. procera under salinity. Moreover, this species was able to maintain a lower Na⁺/K⁺ ratio in the leaves compared to that of the roots of stressed plants. The first response of the root system, after immediate contact with saline solution, present an interesting scenario to discuss.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00957-9.

An Overview of the Characteristics and Potential of Calotropis procera From Botanical, Ecological, and Economic Perspectives

Calotropis procera (Aiton) Dryand. (commonly known as the apple of sodom, calotrope, and giant milkweed) is an evergreen, perennial shrub of the family Apocynaceae, mainly found in arid and semi-arid regions. It is a multipurpose plant, which can be utilized for medicine, fodder, and fuel purposes, timber and fiber production, phytoremediation, and synthesis of nanoparticles. It has been widely used in traditional medicinal systems across North Africa, Middle East Asia, and South-East Asia. At present, it is being extensively explored for its potential pharmacological applications. Several reports also suggest its prospects in the food, textile, and paper industries. Besides, C. procera has also been acknowledged as an ornamental species. High pharmacological potential and socio-economic value have led to the pantropical introduction of the plant. Morpho-physiological adaptations and the ability to tolerate various abiotic stresses enabled its naturalization beyond the introduced areas. Now, it is recognized as an obnoxious environmental weed in several parts of the world. Its unnatural expansion has been witnessed in the regions of South America, the Caribbean Islands, Australia, the Hawaiian Islands, Mexico, Seychelles, and several Pacific Islands. In Australia, nearly 3.7 million hectares of drier areas, including rangelands and Savannahs, have been invaded by the plant. In this review, multiple aspects of C. procera have been discussed including its general characteristics, current and potential uses, and invasive tendencies. The objectives of this review are a) to compile the information available in the literature on C. procera, to make it accessible for future research, b) to enlist together its potential applications being investigated in different fields, and c) to acknowledge C. procera as an emerging invasive species of arid and semi-arid regions.

Metabolomics integrated with transcriptomics: assessing the central metabolism of marine red yeast Sporobolomyces pararoseus under salinity stress

Salinity stress is one of the most serious environmental issues in agricultural regions worldwide. Excess salinity inhibits root growth of various crops, and results in reductions of yield. It is of crucial to understand the molecular mechanisms mediating salinity stress responses for enhancing crops' salt tolerance. Marine red yeast Sporobolomyces pararoseus should have evolved some unique salt-tolerant mechanism, because they long-term live in high-salt ecosystems. However, little research has conducted so far by considering S. pararoseus as model microorganisms to study salt-tolerant mechanisms. Here, we successfully integrated metabolomics with transcriptomic profiles of S. pararoseus in response to salinity stress. Screening of metabolite features with untargeted metabolic profiling, we characterized 4862 compounds from the LC-MS/MS-based datasets. The integrated results showed that amino acid metabolism, carbohydrate metabolism, and lipid metabolism is significantly enriched in response to salt stress. Co-expression network analysis showed that 28 genes and 8 metabolites play an important role in the response of S. pararoseus, which provides valuable clues for subsequent validation. Together, the results provide valuable information for assessing the central metabolism of mediating salt responses in S. pararoseus and offer inventories of target genes for salt tolerance improvement via genetic engineering.

The Full-Length Transcriptome of Spartina alterniflora Reveals the Complexity of High Salt Tolerance in Monocotyledonous Halophyte

Spartina alterniflora (Spartina) is the only halophyte in the salt marsh. However, the molecular basis of its high salt tolerance remains elusive. In this study, we used Pacific Biosciences (PacBio) full-length single-molecule long-read sequencing and RNA-seq to elucidate the transcriptome dynamics of high salt tolerance in Spartina by salt gradient experiments. High-quality unigenes, transcription factors, non-coding RNA and Spartina-specific transcripts were identified. Co-expression network analysis found that protein kinase-encoding genes (SaOST1, SaCIPK10 and SaLRRs) are hub genes in the salt tolerance regulatory network. High salt stress induced the expression of transcription factors but repressed the expression of long non-coding RNAs. The Spartina transcriptome is closer to rice than Arabidopsis, and a higher proportion of transporter and transcription factor-encoding transcripts have been found in Spartina. Transcriptome analysis showed that high salt stress induced the expression of carbohydrate metabolism, especially cell-wall biosynthesis-related genes in Spartina, and repressed its expression in rice. Compared with rice, high salt stress highly induced the expression of stress response, protein modification and redox-related gene expression and greatly inhibited translation in Spartina. High salt stress also induced alternative splicing in Spartina, while differentially expressed alternative splicing events associated with photosynthesis were overrepresented in Spartina but not in rice. Finally, we built the SAPacBio website for visualizing full-length transcriptome sequences, transcription factors, ncRNAs, salt-tolerant genes and alternative splicing events in Spartina. Overall, this study suggests that the salt tolerance mechanism in Spartina is different from rice in many aspects and is far more complex than expected.

Transcriptomic and metabolomic analyses of Lycium ruthenicum and Lycium barbarum fruits during ripening

Red wolfberry (or goji berry, Lycium barbarum; LB) is an important agricultural product with a high content of pharmacologically important secondary metabolites such as phenylpropanoids. A close relative, black wolfberry (L. ruthenicum; LR), endemic to the salinized deserts of northwestern China, is used only locally. The two fruits exhibit many morphological and phytochemical differences, but genetic mechanisms underlying them remain poorly explored. In order to identify the genes of interest for further studies, we studied transcriptomic (Illumina HiSeq) and metabolomic (LC-MS) profiles of the two fruits during five developmental stages (young to ripe). As expected, we identified much higher numbers of significantly differentially regulated genes (DEGs) than metabolites. The highest numbers were identified in pairwise comparisons including the first stage for both species, but total numbers were consistently somewhat lower for the LR. The number of differentially regulated metabolites in pairwise comparisons of developmental stages varied from 66 (stages 3 vs 4) to 133 (stages 2 vs 5) in both species. We identified a number of genes (e.g. AAT1, metE, pip) and metabolites (e.g. rutin, raffinose, galactinol, trehalose, citrulline and DL-arginine) that may be of interest to future functional studies of stress adaptation in plants. As LB is also highly suitable for combating soil desertification and alleviating soil salinity/alkalinity/pollution, its potential for human use may be much wider than its current, highly localized, relevance.

A Gene Regulatory Network Controlled by BpERF2 and BpMYB102 in Birch under Drought Conditions

Gene expression profiles are powerful tools for investigating mechanisms of plant stress tolerance. Betula platyphylla (birch) is a widely distributed tree, but its drought-tolerance mechanism has been little studied. Using RNA-Seq, we identified 2917 birch genes involved in its response to drought stress. These drought-responsive genes include the late embryogenesis abundant (LEA) family, heat shock protein (HSP) family, water shortage-related and ROS-scavenging proteins, and many transcription factors (TFs). Among the drought-induced TFs, the ethylene responsive factor (ERF) and myeloblastosis oncogene (MYB) families were the most abundant. BpERF2 and BpMYB102, which were strongly induced by drought and had high transcription levels, were selected to study their regulatory networks. BpERF2 and BpMYB102 both played roles in enhancing drought tolerance in birch. Chromatin immunoprecipitation combined with qRT-PCR indicated that BpERF2 regulated genes such as those in the LEA and HSP families, while BpMYB102 regulated genes such as Pathogenesis-related Protein 1 (PRP1) and 4-Coumarate:Coenzyme A Ligase 10 (4CL10). Multiple genes were regulated by both BpERF2 and BpMYB102. We further characterized the function of some of these genes, and the genes that encode Root Primordium Defective 1 (RPD1), PRP1, 4CL10, LEA1, SOD5, and HSPs were found to be involved in drought tolerance. Therefore, our results suggest that BpERF2 and BpMYB102 serve as transcription factors that regulate a series of drought-tolerance genes in B. platyphylla to improve drought tolerance.

Reference genes selection for Calotropis procera under different salt stress conditions

Calotropis procera is a perennial Asian shrub with significant adaptation to adverse climate conditions and poor soils. Given its increased salt and drought stress tolerance, C. procera stands out as a powerful candidate to provide alternative genetic resources for biotechnological approaches. The qPCR (real-time quantitative polymerase chain reaction), widely recognized among the most accurate methods for quantifying gene expression, demands suitable reference genes (RGs) to avoid over- or underestimations of the relative expression and incorrect interpretation. This study aimed at evaluating the stability of ten RGs for normalization of gene expression of root and leaf of C. procera under different salt stress conditions and different collection times. The selected RGs were used on expression analysis of three target genes. Three independent experiments were carried out in greenhouse with young plants: i) Leaf₁₀₀ = leaf samples collected 30 min, 2 h, 8 h and 45 days after NaCl-stress (100 mM NaCl); ii) Root₅₀ and iii) Root₂₀₀ = root samples collected 30 min, 2 h, 8 h and 1day after NaCl-stress (50 and 200 mM NaCl, respectively). Stability rank among the three algorithms used showed high agreement for the four most stable RGs. The four most stable RGs showed high congruence among all combination of collection time, for each software studied, with minor disagreements. CYP23 was the best RG (rank of top four) for all experimental conditions (Leaf₁₀₀, Root_50, and Root₂₀₀). Using appropriated RGs, we validated the relative expression level of three differentially expressed target genes (NAC78, CNBL4, and ND1) in Leaf₁₀₀ and Root₂₀₀ samples. This study provides the first selection of stable reference genes for C. procera under salinity. Our results emphasize the need for caution when evaluating the stability RGs under different amplitude of variable factors.

Strengthening desert plant biotechnology research in the United Arab Emirates: a viewpoint

The biotechnology of desert plants is a vast subject. The main applications in this broad field of study comprises of plant tissue culture, genetic engineering, molecular markers and others. Biotechnology applications have the potential to address biodiversity conservation as well as agricultural, medicinal, and environmental issues. There is a need to increase our knowledge of the genetic diversity through the use of molecular genetics and biotechnological approaches in desert plants in the Arabian Gulf region including those in the United Arab Emirates (UAE). This article provides a prospective research for the study of UAE desert plant diversity through DNA fingerprinting as well as understanding the mechanisms of both abiotic stress resistance (including salinity, drought and heat stresses) and biotic stress resistance (including disease and insect resistance). Special attention is given to the desert halophytes and their utilization to alleviate the salinity stress, which is one of the major challenges in agriculture. In addition, symbioses with microorganisms are thought to be hypothesized as important components of desert plant survival under stressful environmental conditions. Thus, factors shaping the diversity and functionality of plant microbiomes in desert ecosystems are also emphasized in this article. It is important to establish a critical mass for biotechnology research and applications while strengthening the channels for collaboration among research/academic institutions in the area of desert plant biotechnology.

Plant Life in Extreme Environments: How Do You Improve Drought Tolerance?

Systems studies of drought stress in resurrection plants and other xerophytes are rapidly identifying a large number of genes, proteins and metabolites that respond to severe drought stress or desiccation. This has provided insight into drought resistance mechanisms, which allow xerophytes to persist under such extreme environmental conditions. Some of the mechanisms that ensure cellular protection during severe dehydration appear to be unique to desert species, while many other stress signaling pathways are in common with well-studied model and crop species. However, despite the identification of many desiccation inducible genes, there are few "gene-to-field" examples that have led to improved drought tolerance and yield stability derived from resurrection plants, and only few examples have emerged from model species. This has led to many critical reviews on the merit of the experimental approaches and the type of plants used to study drought resistance mechanisms. This article discusses the long-standing arguments between the ecophysiology and molecular biology communities, on how to "drought-proof" future crop varieties. It concludes that a more positive and inclusive dialogue between the different disciplines is needed, to allow us to move forward in a much more constructive way.