Understanding the facets of extreme land plant adaptation from transcriptome analysis
Extremophile land plants have evolved convergently to become tough survivors in harsh soil and climatic conditions, such as extremes of soil pH, temperature, drought, high salinity, heavy metals, high light intensity, and UV radiation. Thus, the extremophile plants hold the potential key to improving stress-resilience in crop plants in the face of global climate change and desertification. Moreover, extremophile plants also exhibit industrial importance, being the source of active pharmaceuticals, new fuels, and essential chemicals. Transcriptome analysis of extremophiles is a common approach towards discovering genes and molecular mechanisms for adaptation to stress apart from identifying the pathways responsible for the biosynthesis of commercially essential metabolites. Again, the current scenario in extremophile research ranges from the study of extremophile plant models, e.g., Arabidopsis lyrata, to various plants of economic and ecological significance. The genetic signatures obtained from the transcriptome libraries of these extremophiles are utilized towards their conservation by employing the genome-editing approaches apart from extending their applicability towards the introgression of abiotic tolerance traits into agronomically important crop plants. This chapter aims to summarize the recent transcriptome analyses of extremophile species from the Indian Thar desert and other extreme eco-regions of the world.
Peribacillus frigoritolerans T7-IITJ, a potential biofertilizer, induces plant growth-promoting genes of Arabidopsis thaliana
Aims: This study aimed to isolate plant growth and drought tolerance-promoting bacteria from the nutrient-poor rhizosphere soil of Thar desert plants and unravel their molecular mechanisms of plant growth promotion. Methods and results: Among our rhizobacterial isolates, Enterobacter cloacae C1P-IITJ, Kalamiella piersonii J4-IITJ, and Peribacillus frigoritolerans T7-IITJ, significantly enhanced root and shoot growth (4 - 5-fold) in Arabidopsis thaliana under PEG-induced drought stress. Whole genome sequencing and biochemical analyses of the non-pathogenic bacterium T7-IITJ revealed its plant growth-promoting traits, viz., solubilization of phosphate (40-73 μg/ml), iron (24 ± 0.58 mm halo on chrome azurol S media), and nitrate (1.58 ± 0.01 μg/ml nitrite), along with production of exopolysaccharides (125 ± 20 μg/ml) and auxin-like compounds (42.6 ± 0.05 μg/ml). Transcriptome analysis of A. thaliana inoculated with T7-IITJ and exposure to drought revealed the induction of 445 plant genes (log2fold-change > 1, FDR < 0.05) for photosynthesis, auxin and jasmonate signalling, nutrient uptake, redox homeostasis, and secondary metabolite biosynthesis pathways related to beneficial bacteria-plant interaction, but repression of 503 genes (log2fold-change < -1) including many stress-responsive genes. T7-IITJ enhanced proline 2.5-fold, chlorophyll 2.5 - 2.8-fold, iron 2-fold, phosphate 1.6-fold, and nitrogen 4-fold, and reduced reactive oxygen species 2 - 4.7-fold in plant tissues under drought. T7-IITJ also improved the germination and seedling growth of Tephrosia purpurea, Triticum aestivum, and Setaria italica under drought and inhibited the growth of two plant pathogenic fungi, Fusarium oxysporum, and Rhizoctonia solani. Conclusions: P. frigoritolerans T7-IITJ is a potent biofertilizer that regulates plant genes to promote growth and drought tolerance.
Isolation of plant growth-promoting rhizobacteria from the agricultural fields of Tattiannaram, Telangana
Background: Plant probiotics bacteria are live microbes that promote soil health and plant growth and build the stress-tolerant capacity to the plants. They benefit the plants by increasing nutrient absorption and release of stress-related phytohormones. These plant probiotic bacteria serve a better purpose to the plant when compared to chemical fertilizers. Use of chemical fertilizers such as arsenic and cadmium can lead to soil acidification and even release of harmful gases such as methane which further pollutes the environment. Results: Different bacterial species were isolated from the agricultural fields of Tattiannaram, Telangana, and identified as the efficient rhizosphere bacteria with the essential qualities of plant growth promotion by evaluating the nitrogen-fixing ability on a selective media and various other methods. Upon the molecular characterization of the isolates, they were identified as Corynebacterium spp., Bacillus spp., Lactobacillus spp., and Cytobacillus spp. The results were also examined using various bioinformatics tools for accuracy in their phylogenetic pattern. Conclusion: The recognized species of plant probiotics have established roles in promoting plant growth and strengthening plant immunity. This research introduces an innovative methodology for evaluating and investigating recently identified bacterial isolates, focusing on their distinctive plant probiotic attributes. Through harnessing the potential of advantageous microorganisms and comprehending their interaction with plants and soil, our objective is to formulate inventive approaches to elevate crop productivity, enhance soil richness, and foster environmentally sustainable and robust agricultural methodologies. These characteristics exhibit promising potential for future incorporation into plant systems, fortifying growth and development, and underscoring their distinctive significance within the realm of agriculture.
Rhizosphere Priestia species altered cowpea root transcriptome and enhanced growth under drought and nutrient deficiency
Main Conclusion: Priestia species isolated from the cowpea rhizosphere altered the transcriptome of cowpea roots by colonization and enhanced nutrient uptake, antioxidant mechanisms, and photosynthesis, protecting cowpea from drought and nutrient deficiency. Abstract: Cowpea is a significant grain legume crop primarily grown in sub-Saharan Africa, Asia, and South America. Drought and nutrient deficiency affect the growth and yield of cowpea. To address this challenge, we studied the phyto-beneficial effects of stress-tolerant rhizobacteria on the biomass yield of cowpea under water- and nutrient-deficit conditions. Among the bacteria isolated, two rhizobacillus genotypes, C8 (Priestia filamentosa; basonym: Bacillus filamentosus) and C29 (Priestia aryabhattai; basonym: Bacillus aryabhattai) were evaluated for the improvement of seed germination and growth of cowpea under stress. Our study revealed that C8 protected cowpea from stress by facilitating phosphorus and potassium uptake, protecting it from oxidative damage, reducing transpiration, and enhancing CO2 assimilation. A 17% increase in root biomass upon C8 inoculation was concomitant with the induction of stress tolerance genes in cowpea roots predominantly involved in growth and metabolic processes, cell wall organization, ion homeostasis, and cellular responses to phosphate starvation. Our results indicate a metabolic alteration in cowpea root triggered by P. filamentosa, leading to efficient nutrient reallocation in the host plant. We propose inoculation with P. filamentosa as an effective strategy for improving the yield of cowpea in low-input agriculture, where chemical fertilization and irrigation are less accessible to resource-poor farmers.
How do plants remember drought?
Main conclusion: Plants develop both short-term and transgenerational memory of drought stress through epigenetic regulation of transcription for a better response to subsequent exposure. Abstract: Recurrent spells of droughts are more common than a single drought, with intermittent moist recovery intervals. While the detrimental effects of the first drought on plant structure and physiology are unavoidable, if survived, plants can memorize the first drought to present a more robust response to the following droughts. This includes a partial stomatal opening in the watered recovery interval, higher levels of osmoprotectants and ABA, and attenuation of photosynthesis in the subsequent exposure. Short-term drought memory is regulated by ABA and other phytohormone signaling with transcriptional memory behavior in various genes. High levels of methylated histones are deposited at the drought-tolerance genes. During the recovery interval, the RNA polymerase is stalled to be activated by a pause-breaking factor in the subsequent drought. Drought leads to DNA demethylation near drought-response genes, with genetic control of the process. Progenies of the drought-exposed plants can better adapt to drought owing to the inheritance of particular methylation patterns. However, a prolonged watered recovery interval leads to loss of drought memory, mediated by certain demethylases and chromatin accessibility factors. Small RNAs act as critical regulators of drought memory by altering transcript levels of drought-responsive target genes. Further studies in the future will throw more light on the genetic control of drought memory and the interplay of genetic and epigenetic factors in its inheritance. Plants from extreme environments can give queues to understanding robust memory responses at the ecosystem level.
Identification of differentially expressed mungbean miRNAs and their targets in response to drought stress by small RNA deep sequencing
MicroRNAs (miRNAs) are small, non-coding RNAs, 18–25 nt in length, that play a crucial role in regulating genes associated with the physiological processes and responses to various biotic and abiotic stresses. Different conserved and species-specific microRNAs and their functions have been identified, primarily in plants such as rice and Arabidopsis with sequenced genomes. Our present study identifies drought-responsive miRNAs and their potential targets from mungbean under three days of drought stress induced by PEG-6000. We constructed small RNA libraries from both control and drought-treated tolerant and susceptible mungbean genotypes and identified various miRNAs involved in drought stress regulation. Analysis of differentially expressed genes (DEGs) revealed 79 up-regulated and 158 down-regulated novel miRNAs and two up-and down-regulated known miRNAs under drought. Annotation of the miRNAs followed by target prediction and expression analysis revealed five miRNAs, Vra-miR160, Vra-miR164, Vra-miR167, Vra-miR394, and Vra-miR398, were potentially involved in the regulation of drought-responsive genes. Their predicted target genes were an Auxin response factor (ARF), a NAC (for petunia NAM and Arabidopsis ATAF1, ATAF2, and CUC2) transcription factor, Serine acetyltransferase 1, and Multicopper oxidase LPR2-like. The expression of drought-responsive miRNAs and their targets were validated by real-time PCR. Our data suggest that various known and novel microRNAs activated transcription factors, enzyme kinases, and hormone signaling pathways alleviate drought stress in the tolerant K-851 genotype of mungbean.
Isolation and Characterization of Stress-Tolerant Priestia Species from Cowpea Rhizosphere Under Drought and Nutrient Deficit Conditions
This study aimed to isolate stress-tolerant phytobeneficial bacteria as bio-inoculants for cowpea's sustainable growth under drought and nutrient deficiency conditions. However, the application successful of phytobeneficial bacteria is subject to effective in vitro screening under different physiological conditions. We isolated several Priestia species from cowpea rhizosphere that tolerates polyethylene glycol (PEG6000)-induced drought and nutrient deficiency. Of them, C8 (Priestia filamentosa; basonym: Bacillus filamentosus), followed by C29 (Priestia aryabhattai; basonym: Bacillus aryabhattai), tolerated up to 20% PEG in a low-nutrient medium. In the presence of PEG, Priestia filamentosa and Bacillus aryabhattai exhibited optimal growth in different temperatures and pH but failed to survive at extreme temperatures of 45 °C and pH 11. Priestia filamentosa preferred L-proline and L-glutamate, while L-tryptophan and L-tyrosine were the least utilized. Interestingly, Priestia filamentosa and Bacillus aryabhattai used more complex nitrogen sources, peptone, and yeast extract, than inorganic nitrogen for growth. Most importantly, under drought and nutrient deficiency, Priestia filamentosa exhibited multiple plant growth-promoting traits and more amylase and protease production than C29. Our results indicate that Priestia filamentosa is a potential bacterium to enhance the growth of cowpea plants under stressful conditions.
In silico characterization of five novel disease-resistance proteins in Oryza sativa sp. japonica against bacterial leaf blight and rice blast diseases
In the current study, gene network analysis revealed five novel disease-resistance proteins against bacterial leaf blight (BB) and rice blast (RB) diseases caused by Xanthomonas oryzae pv. oryzae (Xoo) and Magnaporthe oryzae (M. oryzae), respectively. In silico modeling, refinement, and model quality assessment were performed to predict the best structures of these five proteins and submitted to ModelArchive for future use. An in-silico annotation indicated that the five proteins functioned in signal transduction pathways as kinases, phospholipases, transcription factors, and DNA-modifying enzymes. The proteins were localized in the nucleus and plasma membrane. Phylogenetic analysis showed the evolutionary relation of the five proteins with disease-resistance proteins (XA21, OsTRX1, PLD, and HKD-motif-containing proteins). This indicates similar disease-resistant properties between five unknown proteins and their evolutionary-related proteins. Furthermore, gene expression profiling of these proteins using public microarray data showed their differential expression under Xoo and M. oryzae infection. This study provides an insight into developing disease-resistant rice varieties by predicting novel candidate resistance proteins, which will assist rice breeders in improving crop yield to address future food security through molecular breeding and biotechnology.
Enhanced osmotic adjustment, antioxidant defense, and photosynthesis efficiency under drought and heat stress of transgenic cowpea overexpressing an engineered DREB transcription factor
Cowpea is sensitive to drought and heat stress, particularly at the reproductive stages of development. Both stresses limit growth and yield, and their effect is more devastating when occurring concurrently. Dehydration-responsive element-binding protein 2A (DREB2A) is an important signaling hub integrating information about two different abiotic stresses, drought and heat. We identified VuDREB2A as a canonical DREB ortholog in cowpea, activating downstream stress-responsive genes by binding to DREs in their promoter. Post-translational modification of a negative regulatory domain (NRD) within the VuDREB2A protein prevents its degradation. Targeted deletion of the NRD produces a stable and constitutively active form VuDREB2A-CA. However, there is very little evidence of its practical utility under field conditions. This study overexpressed the VuDREB2A-CA in a popular cowpea variety and conducted drought- and heat-tolerance experiments across various stress regimes. Transgenic cowpea exhibited significant tolerance with consistently higher yield when exposed to over 30-d drought stress and 3-d exposure to high temperature (28 °C˗52 °C) without any pleiotropic alterations. The transgenic lines showed higher photosynthetic efficiency, osmotic adjustment, antioxidant defense, thermotolerance, and significantly higher survival and increased biomass than the wild type. Late embryogenesis abundant 5, heat shock protein 70, dehydrin, mitogen-activated protein kinase 2/4, isoflavonoid reductase, and myoinositol phosphate synthase were upregulated in transgenic lines under drought and heat stress. Through transcriptome analysis of the transgenic lines, we found significant up-regulation of various stress-responsive cowpea genes, having DRE in their promoter. Our results suggest that overexpression of VuDREB2A could improve cowpea production under drought and high temperatures.
Aluminum Stress Tolerance in Plants: Insights from Omics Approaches
Aluminum (Al) toxicity in acid soil is one of the most severe environmental stress factors that limit world food production. Al ion (Al 3+) is highly reactive with negatively charged ligands of the cell and disturbs cell division and expansion at sub-micromolar levels. Since the harmful effects are caused by both cyto- and genotoxicities of Al, plant cells show various dose- and time-dependent responses. On the other hand, plants have evolved different Al tolerance strategies that protect sensitive cells from Al 3+ . These include restructuring of the cell wall to prevent deposition of Al 3+ and organic acid release by plasma membrane transporters to chelate out and exclude Al 3+ in the rhizosphere, regulated by the transcription factor STOP1 or its orthologs, and internal detoxification mechanisms including root-to-shoot translocation, antioxidant defense, and Al sequestration in vacuoles to prevent cytotoxicity. In recent years, genomics approaches, particularly genome-wide association studies and transcriptome analyses, have provided genetic evidence of well-known genes’ involvement in Al tolerance and uncovered new Al tolerance genes in plants. This chapter summarizes the findings from recent genomic studies that add to our understanding of the complex plant responses to Al toxicity.