Plant Resistance to Abiotic Stresses

Deleterious Effects of Heat Stress on the Tomato, Its Innate Responses, and Potential Preventive Strategies in the Realm of Emerging Technologies

The tomato is a fruit vegetable rich in nutritional and medicinal value grown in greenhouses and fields worldwide. It is severely sensitive to heat stress, which frequently occurs with rising global warming. Predictions indicate a 0.2 °C increase in average surface temperatures per decade for the next three decades, which underlines the threat of austere heat stress in the future. Previous studies have reported that heat stress adversely affects tomato growth, limits nutrient availability, hammers photosynthesis, disrupts reproduction, denatures proteins, upsets signaling pathways, and damages cell membranes. The overproduction of reactive oxygen species in response to heat stress is toxic to tomato plants. The negative consequences of heat stress on the tomato have been the focus of much investigation, resulting in the emergence of several therapeutic interventions. However, a considerable distance remains to be covered to develop tomato varieties that are tolerant to current heat stress and durable in the perspective of increasing global warming. This current review provides a critical analysis of the heat stress consequences on the tomato in the context of global warming, its innate response to heat stress, and the elucidation of domains characterized by a scarcity of knowledge, along with potential avenues for enhancing sustainable tolerance against heat stress through the involvement of diverse advanced technologies. The particular mechanism underlying thermotolerance remains indeterminate and requires further elucidatory investigation. The precise roles and interplay of signaling pathways in response to heat stress remain unresolved. The etiology of tomato plants' physiological and molecular responses against heat stress remains unexplained. Utilizing modern functional genomics techniques, including transcriptomics, proteomics, and metabolomics, can assist in identifying potential candidate proteins, metabolites, genes, gene networks, and signaling pathways contributing to tomato stress tolerance. Improving tomato tolerance against heat stress urges a comprehensive and combined strategy including modern techniques, the latest apparatuses, speedy breeding, physiology, and molecular markers to regulate their physiological, molecular, and biochemical reactions.

Transformation and expressional studies of GaZnF gene to improve drought tolerance in Gossypium hirsutum

Drought stress is the major limiting factor in plant growth and production. Cotton is a significant crop as textile fiber and oilseed, but its production is generally affected by drought stress, mainly in dry regions. This study aimed to investigate the expression of Zinc finger transcription factor's gene (GaZnF) to enhance the drought tolerance in Gossypium hirsutum. Sequence features of the GaZnF protein were recognized through different bioinformatics tools like multiple sequence alignment analysis, phylogenetic tree for evolutionary relationships, Protein motifs, a transmembrane domain, secondary structure and physio-chemical properties indicating that GaZnF is a stable protein. CIM-482, a local Gossypium hirsutum variety was transformed with GaZnF through Agrobacterium-mediated transformation method with 2.57% transformation efficiency. The integration of GaZnF was confirmed through Southern blot showing 531 bp, and Western blot indicated a 95 kDa transgene-GUS fusion band in transgenic plants. The normalized real-time expression analysis revealed the highest relative fold spatial expression of cDNA of GaZnF within leaf tissues at vegetative and flowering stages under drought stress. Morphological, physiological and biochemical parameters of transgenic cotton plants at 05- and 10-day drought stress was higher than those of non-transgenic control plants. The values of fresh and dry biomass, chlorophyll content, photosynthesis, transpiration rate, and stomatal conductance reduced in GaZnF transgenic cotton plants at 05- and 10-day drought stress, but their values were less low in transgenic plants than those of non-transgenic control plants. These findings showed that GaZnF gene expression in transgenic plants could be a valuable source for the development of drought-tolerant homozygous lines through breeding.

Identification of simple sequence repeat markers linked to heat tolerance in rice using bulked segregant analysis in F2 population of NERICA-L 44 × Uma

The damage caused by high temperature is one of the most important abiotic stress affecting rice production. Reproductive stage of rice is highly susceptible to high temperature. The present investigation was undertaken to identify polymorphic microsatellite markers (SSR) associated with heat tolerance. The rice cultivars NERICA- L 44 (heat tolerant) and Uma (heat susceptible) were crossed to generate F¹ and F² populations. The F² population was subjected to heat stress at >38°C and the 144 F² plants were evaluated for their tolerance. The results note that the mean of the F² population was influenced by the tolerant parent with regards to the traits of plant height, membrane stability index, photosynthetic rate, stomatal conductance, evapotranspiration rate, pollen viability, spikelet fertility and 1000 grain weight. Ten each of the extremely susceptible and tolerant plants were selected based on the spikelet fertility percentage. Their DNA was pooled into tolerant and susceptible bulks and Bulked Segregant Analysis (BSA) was carried out using 100 SSR markers to check for polymorphism. The survey revealed a polymorphism of 18% between the parents. RM337, RM10793, RM242, RM5749, RM6100, RM490, RM470, RM473, RM222 and RM556 are some of the prominent markers that were found to be polymorphic between the parents and the bulks. We performed gene annotation and enrichment analysis of identified polymorphic markers. Result revealed that the sequence specific site of that chromosome mostly enriched with biological processes like metabolic pathway, molecular mechanism, and subcellular function. Among that RM337 was newly reported marker for heat tolerance. Expression analysis of two genes corresponds to RM337 revealed that LOP1 (LOC_Os08g01330) was linked to high temperature tolerance in rice. The results demonstrate that BSA using SSR markers is useful in identifying genomic regions that contribute to thermotolerance.

Current trends and insights on EMS mutagenesis application to studies on plant abiotic stress tolerance and development

Ethyl methanesulfonate (EMS)-induced mutagenesis is a powerful tool to generate genetic resource for identifying untapped genes and characterizing the function of genes to understand the molecular basis of important agronomic traits. This review focuses on application of contemporary EMS mutagenesis in the field of plant development and abiotic stress tolerance research, with particular focuses on reviewing the mutation types, mutagenesis site, mutagen concentration, mutagenesis duration, the identification and characterization of mutations responsible for altered stress tolerance responses. The application of EMS mutation breeding combined with genetic engineering in the future plant breeding and fundamental research was also discussed. The collective information in this review will provide good insight on how EMS mutagenesis is efficiently applied to improve abiotic stress tolerance of crops with the utilization of Next-generation sequencing (NGS) for mutation identification.

Genome-wide characterization of C2H2 zinc-finger gene family provides insight into the mechanisms and evolution of the dehydration-rehydration responses in Physcomitrium and Arabidopsis

Dehydration tolerance is a vital factor for land plant evolution and world agricultural production. Numerous studies enlightened that the plant-specific C2H2-type zinc-finger proteins (C2H2-ZFPs) as master regulators played pivotal roles in the abiotic stress responses of plants. However, a comprehensive understanding of the evolution of C2H2-ZFPs in terrestrial plants and its regulatory mechanism in dehydration and rehydration response remains a mystery. In this study, the genome-wide identification of C2H2-ZFP genes revealed 549 homologs in the representatives of terrestrial plant lineages from liverwort to angiosperms. Based on the characteristics of the conserved C2H2-ZF domains, four major C2H2-ZF types (M-, Z-, Q-, and D-type) were identified in the C2H2-ZFPs, with the dominants of M-type in all selected species and followed by Z-type in non-seed plants and Q-type in seed plants, respectively. Phylogenetic analyses of the identified C2H2-ZFPs supported four major groups in the land plant representatives, among which the members from the desiccation-tolerant Physcomitrium patens and the dehydration-sensitive Arabidopsis thaliana displayed different topological relationships in the phylogenies reconstructed for a single species. C2H2-ZFPs clustered in the same subclades shared similar features in their conserved domains and gene structures. Approximately, 81% of the C2H2-ZFP promoters of all 549 identified C2H2-ZFPs harbored the conserved ABA-responsive elements (ABREs) and/or dehydration-responsive elements (DREs). Comparative transcriptomic analyses showed that 50 PpZFPs and 56 AtZFPs significantly changed their transcripts abundance. Interestingly, most of the dehydration- and rehydration-responsive PpZPFs and AtZFPs had been predicted to contain the ABRE and DRE elements in their promoter regions and with over half of which phylogenetically belonging to group III. The differences in the expression patterns of C2H2-ZFPs in responses to dehydration and rehydration between P. patens and A. thaliana reflected their different strategies to adapt to dehydration. The identified candidate PpZFPs were specifically induced by moderate dehydration and reached the peak transcript abundance in severe dehydration. Our study lays the foundations for further functional investigation of C2H2-ZFPs in dehydration responses from an evolutionary perspective in land plants. The findings will provide us with genetic resources and potential targets for drought tolerance breeding in crops and beyond.

Endophytic Fungal Consortia Enhance Basal Drought-Tolerance in Moringa oleifera by Upregulating the Antioxidant Enzyme (APX) through Heat Shock Factors

Global climate change has imposed harsh environmental conditions such as drought. Naturally, the most compatible fungal consortia operate synergistically to enhance plant growth and ecophysiological responses against abiotic strains. Yet, little is known about the interactions between phytohormone-producing endophytic fungal symbionts and plant growth under drought stress. The existing research was rationalized to recognize the role of newly isolated drought-resistant, antioxidant-rich endophytic fungal consortia hosting a xerophytic plant, Carthamus oxycantha L., inoculated to Moringa oleifera L. grown under drought stress of 8% PEG (polyethylene glycol-8000). Under drought stress, the combined inoculation of endophytic strain Microdochium majus (WA), Meyerozyma guilliermondi (TG), and Aspergillus aculeatus (TL3) exhibited a significant improvement in growth attributes such as shoot fresh weight (1.71-fold), shoot length (0.86-fold), root length (0.65-fold), dry weight (2.18-fold), total chlorophyll (0.46-fold), and carotenoids (0.87-fold) in comparison to control (8% PEG). Primary and secondary metabolites were also increased in M. oleifera inoculated with endophytic consortia, under drought stress, such as proteins (1.3-fold), sugars (0.58-fold), lipids (0.41-fold), phenols (0.36-fold), flavonoids (0.52-fold), proline (0.6-fold), indole acetic acid (IAA) (4.5-fold), gibberellic acid (GA) (0.7-fold), salicylic acid (SA) (0.8-fold), ascorbic acid (ASA) (1.85-fold), while abscisic acid (ABA) level was decreased (−0.61-fold) in comparison to the control (8% PEG). Under drought stress, combined inoculation (WA, TG, TL3) also promoted the antioxidant activities of enzymes such as ascorbate peroxidase (APX) (3.5-fold), catalase (CAT) activity (1.7-fold), and increased the total antioxidant capacity (TAC) (0.78-fold) with reduced reactive oxygen species (ROS) such as H2O2 production (-0.4-fold), compared to control (8% PEG), and stomatal aperture was larger (3.5-fold) with a lesser decrease (-0.02-fold) in water potential. Moreover, combined inoculation (WA, TG, TL3) up regulated the expression of MolHSF3, MolHSF19, and MolAPX genes in M. oleifera under drought stress, compared to the control (8% PEG), is suggestive of an important regulatory role for drought stress tolerance governed by fungal endophytes. The current research supports the exploitation of the compatible endophytic fungi for establishing the tripartite mutualistic symbiosis in M. oleifera to alleviate the adverse effects of drought stress through strong antioxidant activities.

Bioinformatics approaches and applications in plant biotechnology

BACKGROUND

In recent years, major advance in molecular biology and genomic technologies have led to an exponential growth in biological information. As the deluge of genomic information, there is a parallel growth in the demands of tools in the storage and management of data, and the development of software for analysis, visualization, modelling, and prediction of large data set.

MAIN BODY

Particularly in plant biotechnology, the amount of information has multiplied exponentially with a large number of databases available from many individual plant species. Efficient bioinformatics tools and methodologies are also developed to allow rapid genome sequence and the study of plant genome in the 'omics' approach. This review focuses on the various bioinformatic applications in plant biotechnology, and their advantages in improving the outcome in agriculture. The challenges or limitations faced in plant biotechnology in the aspect of bioinformatics approach that explained the low progression in plant genomics than in animal genomics are also reviewed and assessed.

CONCLUSION

There is a critical need for effective bioinformatic tools, which are able to provide longer reads with unbiased coverage in order to overcome the complexity of the plant's genome. The advancement in bioinformatics is not only beneficial to the field of plant biotechnology and agriculture sectors, but will also contribute enormously to the future of humanity.

Utilizing spectral vegetation indices for yield assessment of tomato genotypes grown in arid conditions

Tomato is among important vegetable crops cultivated in different climates; however, heat stress can greatly affect fruit quality and overall yield. Crop reflectance measurements based on ground reflectance sensor data are reliable indicators of crop tolerance to abiotic stresses. Here, we report on using non-destructive spectral vegetation indices to monitor yield traits of 10 tomato genotypes transplanted on three different dates (Aug. 2, Sept. 3 and Oct. 1) during 2019 growing season in the Riyadh region. The ten genotypes comprised six commercial cultivars–(Pearson Improved, Strain B, Valentine, Marmande VF, Super Strain B, and Pearson early) ––and four local Saudi cultivars (Al-Ahsa, Al-Qatif, Hail and Najran). Spectral reflectance data were utilized using a FieldSpec 3 spectroradiometer in the range of 350–2500 nm to calculate nine vegetation indices (VIs): Normalized Water Band Index (NWBI), Difference Water Index (NDWI), Photochemical Reflectance Index (PRI), Normalized Difference Vegetation Index (NDVI), Green Normalized Difference Vegetation Index (GNDVI), Red Edge Normalized Difference Vegetation Index, Soil Adjusted Vegetation Index (SAVI), Red Edge Normalized Difference Vegetation Index (RENDVI), Renormalized Difference Vegetation Index (RDVI), and Normalized Difference Nitrogen Index (NDNI). VIs and yield parameters (total fruit yield, harvest index) revealed that second transplanting date was optimal for all the genotypes. Valentine showed the best growth performance followed by Najran, Hail, Super Strain B and finally Pearson early. For all the three transplanting dates, Valentine recorded the highest total fruit yield. Additionally, some genotypes had no significant differences in the VIs values or the total fruit yield between the second and third transplanting dates. This study indicated that yield parameters could be linked to rapid, non-destructive hyperspectral reflectance data to predict tomato production under heat stress.

Plant protease as regulator and signaling molecule for enhancing environmental stress-tolerance

Proteases are ubiquitous in prokaryotes and eukaryotes. Plant proteases are key regulators of various physiological processes, including protein homeostasis, organelle development, senescence, seed germination, protein processing, environmental stress response, and programmed cell death. Proteases are involved in the breakdown of peptide bonds resulting in irreversible posttranslational modification of the protein. Proteases act as signaling molecules that specifically regulate cellular function by cleaving and triggering receptor molecules. Peptides derived from proteolysis regulate ROS signaling under oxidative stress in the plant. It degrades misfolded and abnormal proteins into amino acids to repair the cell damage and regulates the biological process in response to environmental stress. Proteases modulate the biogenesis of phytohormones which control plant growth, development, and environmental stresses. Protein homeostasis, the overall balance between protein synthesis and proteolysis, is required for plant growth and development. Abiotic and biotic stresses are major factors that negatively impact cellular survivability, biomass production, and reduced crop yield potentials. Therefore, the identification of various stress-responsive proteases and their molecular functions may elucidate valuable information for the development of stress-resilient crops with higher yield potentials. However, the understanding of molecular mechanisms of plant protease remains unexplored. This review provides an overview of proteases related to development, signaling, and growth regulation to acclimatize environmental stress in plants.

Metabolomics, a Powerful Tool for Understanding Plant Abiotic Stress

Metabolomics is a technology that generates large amounts of data and contributes to obtaining wide and integral explanations of the biochemical state of a living organism. Plants are continuously affected by abiotic stresses such as water scarcity, high temperatures and high salinity, and metabolomics has the potential for elucidating the response-to-stress mechanisms and develop resistance strategies in affected cultivars. This review describes the characteristics of each of the stages of metabolomic studies in plants and the role of metabolomics in the characterization of the response of various plant species to abiotic stresses.

QTL Mapping and Identification of Candidate Genes for Heat Tolerance at the Flowering Stage in Rice

High-temperature stress can cause serious abiotic damage that limits the yield and quality of rice. Heat tolerance (HT) during the flowering stage of rice is a key trait that can guarantee a high and stable yield under heat stress. HT is a complex trait that is regulated by multiple quantitative trait loci (QTLs); however, few underlying genes have been fine mapped and cloned. In this study, the F_2:3 population derived from a cross between Huanghuazhan (HHZ), a heat-tolerant cultivar, and 9311, a heat-sensitive variety, was used to map HT QTLs during the flowering stage in rice. A new major QTL, qHTT8, controlling HT was identified on chromosome 8 using the bulked-segregant analysis (BSA)-seq method. The QTL qHTT8 was mapped into the 3,555,000–4,520,000 bp, which had a size of 0.965 Mb. The candidate region of qHTT8 on chromosome 8 contained 65 predicted genes, and 10 putative predicted genes were found to be associated with abiotic stress tolerance. Furthermore, qRT-PCR was performed to analyze the differential expression of these 10 genes between HHZ and 9311 under high temperature conditions. LOC_Os08g07010 and LOC_Os08g07440 were highly induced in HHZ compared with 9311 under heat stress. Orthologous genes of LOC_Os08g07010 and LOC_Os08g07440 in plants played a role in abiotic stress, suggesting that they may be the candidate genes of qHTT8. Generally, the results of this study will prove useful for future efforts to clone qHTT8 and breed heat-tolerant varieties of rice using marker-assisted selection.

C2H2 Zinc Finger Proteins: Master Regulators of Abiotic Stress Responses in Plants

Abiotic stresses such as drought and salinity are major environmental factors that limit crop yields. Unraveling the molecular mechanisms underlying abiotic stress resistance is crucial for improving crop performance and increasing productivity under adverse environmental conditions. Zinc finger proteins, comprising one of the largest transcription factor families, are known for their finger-like structure and their ability to bind Zn2+. Zinc finger proteins are categorized into nine subfamilies based on their conserved Cys and His motifs, including the Cys2/His2-type (C2H2), C3H, C3HC4, C2HC5, C4HC3, C2HC, C4, C6, and C8 subfamilies. Over the past two decades, much progress has been made in understanding the roles of C2H2 zinc finger proteins in plant growth, development, and stress signal transduction. In this review, we focus on recent progress in elucidating the structures, functions, and classifications of plant C2H2 zinc finger proteins and their roles in abiotic stress responses.